Growth-Arrest-Specific 7 Gene Regulates Neural Crest Formation and Craniofacial Development in Zebrafish

Growth-arrest-specific 7 (Gas7) is preferentially expressed in the nervous system and plays an important role during neuritogenesis in vertebrates. We recently demonstrated that gas7 is highly expressed in zebrafish neurons, where it regulates neural development. The possibility that gas7 may also regulate the development of other tissues remains to be examined. Here we investigate the role of Gas7 in the development of craniofacial tissues. Knockdown of gas7 using morpholino oligomers produced abnormal phenotypes in neural crest cells and their derivatives. Neural crest-derived cartilage maturation was altered in Gas7 morphants as revealed by aberrant sox9b and dlx2 expression, a phenotype which could be rescued by co-injection of gas7 mRNA. While rhombomere morphology remained normal in Gas7 morphants, we observed reduced expression of the pre-chondrogenic genes sox9b and dlx2 in cells populating the posterior pharyngeal arches, but the fundamental structure of pharyngeal arches was preserved. In addition, neural crest cell sublineages that migrate to form neurons, glial cells, and melanocytes were altered in Gas7 morphants as revealed by aberrant expression of neurod, foxd3 and mitfa, respectively. Development of neural crest progenitors was also examined in Gas7 morphants at 12-hpf and we observed that the reduction of cell precursors in Gas7 morphants was due to increased apoptosis level. These results indicate that the formation of neural crest progenitors and derivatives depends on Gas7 expression. Our observations also suggest that Gas7 regulates the formation of neural crest derivatives constituting the internal tissues of pharyngeal arches, without affecting the fundamental structure of mesodermal-derived pharyngeal arches.