| description |
The tongue is a muscular organ in the vertebrate oral cavity that performs complex functions in daily life, including feeding and phonetic articulation. The tongue consists of mesenchyme cells of two distinct origins: the muscle cells are derived from occipital somites whereas the tendons and other connective tissues derived from the cranial neural crest. Cranial neural crest cells are important for the initiation of tongue swelling and proper patterning of intrinsic and extrinsic tongue muscle groups. However, little is known regarding the molecular and cellular mechanisms of tongue morphogenesis. We show that the odd-skipped related 1 (Osr1) transcription factor exhibits dynamic expression in the tongue mesenchyme during early tongue development. Tissue-specific inactivation of Osr1 in the early neural crest cells resulted in ectopic cartilage formation in the mouse tongue. We show that Sox9, the master regulator of chondrocyte differentiation, is initially widely expressed in the neural crest derived mesenchyme in the tongue and subsequently down-regulated concomitant by up-regulation of Osr1 expression. Osr1 mutant embryos exhibit persistent expression of Sox9 and chondrocyte differentiation from the neural crest derived tongue mesenchyme. Further biochemical analyses indicate that Osr1 may directly suppresses Sox9 gene expression in the tongue mesenchyme. These data reveal a novel mechanism in suppression of chondrogenic fate during tongue development. Remarkably, the ectopic cartilage in the Osr1 mutant mice resembles the entoglossal cartilage naturally develops in the avian tongue. These results suggest that modulation of expression of Osr1 may underline the evolutionary divergence in tongue cartilage formation.RNAs were isolated from microdissected E12 embryonic mouse tongue of Osr1f/-;Wnt1cre and control littermates and characterized by RNAseqOverall design: E12 mouse embryonic tongues were micro-dissceted, 3 pairs of control and mutant samples were pooled for the RNA extraction |