Transcription factor Ap-2 alpha is necessary for development of embryonic melanophores, autonomic neurons and pharyngeal skeleton in zebrafish

Abstract

The genes that control development of embryonic melanocytes are poorly defined. Although transcription factor Ap-2a is expressed in neural crest (NC) cells, its role in development of embryonic melanocytes and other neural crest derivatives is unclear because mouse Ap-2a mutants die before melanogenesis. We show that zebrafish embryos injected with morpholino antisense oligonucleotides complementary to ap-2a (ap-2a MO) complete early morphogenesis normally and have neural crest cells. Expression of c-kit, which encodes the receptor for the Steel ligand, is reduced in these embryos, and, similar to zebrafish c-kit mutant embryos, embryonic melanophores are reduced in number and migration. The effects of ap-2a MO injected into heterozygous and homozygous c-kit mutants support the notion that Ap-2a works through C-kit and additional target genes to mediate melanophore cell number and migration. In contrast to c-kit mutant embryos, in ap-2a MO-injected embryos, melanophores are small and under-pigmented, and unexpectedly, analysis of mosaic embryos suggests Ap-2a regulates melanophore differentiation through cell non-autonomous targets. In addition to melanophore phenotypes, we document reduction of other neural crest derivatives in ap-2a MO-injected embryos, including jaw cartilage, enteric neurons, and sympathetic neurons. These results reveal that Ap-2a regulates multiple steps of melanophore development, and is required for development of other neuronal and nonneuronal neural crest derivatives.