SRX23810565 GSM8122649_r1 SRP492834 PRJNA1082682 SRS20633428 GSM8122649 GSM8122649 ATAC-seq GENOMIC other Four hearts at E9.5 were pooled per genotype per replicate, and were then dissociated into single cells. 40,000 viable cells were taken for were lysed to isolate nuclei, which were treated with Tn5 transposase (Nextera DNA Sample Prep Kit, Illumina) to isolate DNA. Fragmented DNA was then amplified using bar-coded PCR primers and libraries were seuqenced. Dissociated embryonic cardiac cells were lysed to isolate nuclei, which were treated with Tn5 transposase (Nextera DNA Sample Prep Kit, Illumina) to isolate DNA Fragmented DNA was then amplified using bar-coded PCR primers and libraries were pooled. Illumina HiSeq 2500 SRX23810566 GSM8122650_r1 SRP492834 PRJNA1082682 SRS20633427 GSM8122650 GSM8122650 ATAC-seq GENOMIC other Four hearts at E9.5 were pooled per genotype per replicate, and were then dissociated into single cells. 40,000 viable cells were taken for were lysed to isolate nuclei, which were treated with Tn5 transposase (Nextera DNA Sample Prep Kit, Illumina) to isolate DNA. Fragmented DNA was then amplified using bar-coded PCR primers and libraries were seuqenced. Dissociated embryonic cardiac cells were lysed to isolate nuclei, which were treated with Tn5 transposase (Nextera DNA Sample Prep Kit, Illumina) to isolate DNA Fragmented DNA was then amplified using bar-coded PCR primers and libraries were pooled. Illumina HiSeq 2500 SRX23810567 GSM8122651_r1 SRP492834 PRJNA1082682 SRS20633429 GSM8122651 GSM8122651 ATAC-seq GENOMIC other Four hearts at E9.5 were pooled per genotype per replicate, and were then dissociated into single cells. 40,000 viable cells were taken for were lysed to isolate nuclei, which were treated with Tn5 transposase (Nextera DNA Sample Prep Kit, Illumina) to isolate DNA. Fragmented DNA was then amplified using bar-coded PCR primers and libraries were seuqenced. Dissociated embryonic cardiac cells were lysed to isolate nuclei, which were treated with Tn5 transposase (Nextera DNA Sample Prep Kit, Illumina) to isolate DNA Fragmented DNA was then amplified using bar-coded PCR primers and libraries were pooled. Illumina HiSeq 2500 SRX23810568 GSM8122652_r1 SRP492834 PRJNA1082682 SRS20633430 GSM8122652 GSM8122652 ATAC-seq GENOMIC other Four hearts at E9.5 were pooled per genotype per replicate, and were then dissociated into single cells. 40,000 viable cells were taken for were lysed to isolate nuclei, which were treated with Tn5 transposase (Nextera DNA Sample Prep Kit, Illumina) to isolate DNA. Fragmented DNA was then amplified using bar-coded PCR primers and libraries were seuqenced. Dissociated embryonic cardiac cells were lysed to isolate nuclei, which were treated with Tn5 transposase (Nextera DNA Sample Prep Kit, Illumina) to isolate DNA Fragmented DNA was then amplified using bar-coded PCR primers and libraries were pooled. Illumina HiSeq 2500