SRX3825259 GSM3057017 SRP136119 SRS3074340 GSM3057017 RNA-Seq TRANSCRIPTOMIC cDNA T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057017 GSM3057017 GEO Accession GSM3057017 SRX3825260 GSM3057018 SRP136119 SRS3074341 GSM3057018 RNA-Seq TRANSCRIPTOMIC cDNA T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057018 GSM3057018 GEO Accession GSM3057018 SRX3825261 GSM3057019 SRP136119 SRS3074342 GSM3057019 RNA-Seq TRANSCRIPTOMIC cDNA T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057019 GSM3057019 GEO Accession GSM3057019 SRX3825262 GSM3057020 SRP136119 SRS3074343 GSM3057020 RNA-Seq TRANSCRIPTOMIC cDNA T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057020 GSM3057020 GEO Accession GSM3057020 SRX3825263 GSM3057021 SRP136119 SRS3074344 GSM3057021 RNA-Seq TRANSCRIPTOMIC cDNA T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057021 GSM3057021 GEO Accession GSM3057021 SRX3825264 GSM3057022 SRP136119 SRS3074345 GSM3057022 RNA-Seq TRANSCRIPTOMIC cDNA T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057022 GSM3057022 GEO Accession GSM3057022 SRX3825265 GSM3057023 SRP136119 SRS3074346 GSM3057023 RNA-Seq TRANSCRIPTOMIC cDNA T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057023 GSM3057023 GEO Accession GSM3057023 SRX3825266 GSM3057024 SRP136119 SRS3074347 GSM3057024 RNA-Seq TRANSCRIPTOMIC cDNA T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057024 GSM3057024 GEO Accession GSM3057024 SRX3825267 GSM3057025 SRP136119 SRS3074348 GSM3057025 RNA-Seq TRANSCRIPTOMIC cDNA T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). Illumina HiSeq 2500 gds 303057025 GSM3057025 GEO Accession GSM3057025 SRX3825268 GSM3057026 SRP136119 SRS3074349 GSM3057026 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057026 GSM3057026 GEO Accession GSM3057026 SRX3825269 GSM3057027 SRP136119 SRS3074350 GSM3057027 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057027 GSM3057027 GEO Accession GSM3057027 SRX3825270 GSM3057028 SRP136119 SRS3074351 GSM3057028 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057028 GSM3057028 GEO Accession GSM3057028 SRX3825271 GSM3057029 SRP136119 SRS3074352 GSM3057029 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057029 GSM3057029 GEO Accession GSM3057029 SRX3825272 GSM3057030 SRP136119 SRS3074353 GSM3057030 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057030 GSM3057030 GEO Accession GSM3057030 SRX3825273 GSM3057031 SRP136119 SRS3074354 GSM3057031 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057031 GSM3057031 GEO Accession GSM3057031 SRX3825274 GSM3057032 SRP136119 SRS3074355 GSM3057032 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057032 GSM3057032 GEO Accession GSM3057032 SRX3825275 GSM3057033 SRP136119 SRS3074356 GSM3057033 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057033 GSM3057033 GEO Accession GSM3057033 SRX3825276 GSM3057034 SRP136119 SRS3074357 GSM3057034 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057034 GSM3057034 GEO Accession GSM3057034 SRX3825277 GSM3057035 SRP136119 SRS3074358 GSM3057035 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057035 GSM3057035 GEO Accession GSM3057035 SRX3825278 GSM3057036 SRP136119 SRS3074359 GSM3057036 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057036 GSM3057036 GEO Accession GSM3057036 SRX3825279 GSM3057037 SRP136119 SRS3074360 GSM3057037 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057037 GSM3057037 GEO Accession GSM3057037 SRX3825280 GSM3057038 SRP136119 SRS3074361 GSM3057038 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057038 GSM3057038 GEO Accession GSM3057038 SRX3825281 GSM3057039 SRP136119 SRS3074362 GSM3057039 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057039 GSM3057039 GEO Accession GSM3057039 SRX3825282 GSM3057040 SRP136119 SRS3074363 GSM3057040 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057040 GSM3057040 GEO Accession GSM3057040 SRX3825283 GSM3057041 SRP136119 SRS3074364 GSM3057041 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057041 GSM3057041 GEO Accession GSM3057041 SRX3825284 GSM3057042 SRP136119 SRS3074365 GSM3057042 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057042 GSM3057042 GEO Accession GSM3057042 SRX3825285 GSM3057043 SRP136119 SRS3074366 GSM3057043 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057043 GSM3057043 GEO Accession GSM3057043 SRX3825286 GSM3057044 SRP136119 SRS3074367 GSM3057044 ATAC-seq GENOMIC other T18, T20 and T21 dorsal neural tubes including premigratory, migrating and/or post-migratory neural crest cells were dissected from the head using an eye-lash knife. T20 and T23 heads were dissected using forceps. For RNA-seq, tissue was lysed in the Ambion RNaqueous Total RNA Isolation kit lysis buffer (AM1931), set on ice for 15 minutes with occasional vortexing, flash frozen in liquid nitrogen and stored at -80°C. RNA was extracted using the Ambion RNAqueous Micro Total RNA isolation kit and assessed using the Agilent Bioanalyser. For ATAC-seq, groups of dissected tissue were collected into L-15 medium (Lifetech) with 10% fetal bovine serum at 19°C. Tissue was first dissociated in dispase (1.5 mg/ml in DMEM; 10mM Hepes, pH 7.5), followed by the addition of an equal volume of trypsin (0.05% Trypsin; 0.53mM EDTA in HBSS) at room temperature for a total of up to 15 minutes. Dissociated cells were passed over a 40 μm cell strainer into Hanks' solution (1xHBSS; 10mMHepes; 0.25%BSA) and centrifuged at 500 x g for 7 minutes at room temperature. The supernatant was removed and fresh Hank's solution applied. 50 000 cells were counted out and centrifuged for 5 minutes at 500 × g at 4°C and washed with cold 2/3 phosphate buffered saline (PBS) by centrifugation for 5 minutes at 500 × g, 4°C. 
 RNA-seq libraries were prepared from 100 ng RNA per sample using the NEBNExt Ultra Directional RNA Library Prep Kit for Illumina (E7420) in combination with the NEBNext Poly(A) mRNA Magnetic Isolation Module (E7490) and NEBNext High-Fidelity 2X PCR Master Mix (M0451S). Libraries were indexed and enriched by 15 cycles of amplification. Library preparation was assessed using the Agilent TapeStation and libraries quantified by Qubit. The concentration of library pools was assessed with the KAPA Library Quantification Kit (KK4835). For ATAC-seq, dissociated cells were lysed (10mM Tris-HCl, pH7.4; 10mM NaCl; 3mM MgCl2; 0.1% Igepal) and tagmented using the Illumina Nextera kit (FC-121-1030) for 30 minutes at 37°C as previously described (Buenrostro et al. 2015 Curr Protoc Mol Biol 109, 21 29 21-29, doi:10.1002/0471142727.mb2129s109), with the addition of a tagmentation-stop step by the addition of EDTA to final concentration of 50 nM and incubation at 50°C for 30 minutes. Tagmented DNA was amplified using the NEB Q5 High-Fidelity 2X Master Mix (M0492S) for 14 cycles. Tagmentation efficiency was assessed using Agilent TapeStation and libraries quantified by Qubit. The concentration of ATAC library pools was assessed with the KAPA Library Quantification Kit (KK4835). NextSeq 500 gds 303057044 GSM3057044 GEO Accession GSM3057044