Transcription factor Ap-2α 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-2alpha is expressed in neural crest (NC) cells, its role in development of embryonic melanocytes and other neural crest derivatives is unclear because mouse Ap-2alpha mutants die before melanogenesis. We show that zebrafish embryos injected with morpholino antisense oligonucleotides complementary to ap-2alpha (ap-2alpha 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-2alpha MO injected into heterozygous and homozygous c-kit mutants support the notion that Ap-2alpha works through C-kit and additional target genes to mediate melanophore cell number and migration. In contrast to c-kit mutant embryos, in ap-2alpha MO-injected embryos, melanophores are small and under-pigmented, and unexpectedly, analysis of mosaic embryos suggests Ap-2alpha regulates melanophore differentiation through cell non-autonomous targets. In addition to melanophore phenotypes, we document reduction of other neural crest derivatives in ap-2alpha MO-injected embryos, including jaw cartilage, enteric neurons, and sympathetic neurons. These results reveal that Ap-2alpha regulates multiple steps of melanophore development, and is required for development of other neuronal and non-neuronal neural crest derivatives.

Evolution of the neural crest viewed from a gene regulatory perspective

“…The first apparent difference is that neural crest specifiers appear to be activated in two phases. One set of transcription factors including n-Myc, Id, AP-2 and Snail are deployed earlier than previously noted in higher vertebrates Barrallo-Gimeno et al, 2004;Bellmeyer et al, 2003;Knight et al, 2005;Knight et al, 2003;LaBonne and Bronner-Fraser, 2000;Light et al, 2005;Nieto et al, 1994;O'Brien et al, 2004). These regulators are activated at the neural plate border of the early neurula slightly after neural plate border specifiers (Sauka-Spengler et al, 2007).…”

Mechanisms driving neural crest induction and migration in the zebrafish andXenopus laevis

“…As for the neural crest specifiers, snail2, sox9, sox10, foxd3 and ap-2 family members have been all shown to be important in zebrafish neural crest development. [206][207][208][209][210][211] Knockdown of ap-2a and ap-2c in zebrafish prevents neural crest induction, with no effect on the neural plate border specifiers, but loss of the expression of foxd3 and snail2. 207,208 Interestingly, these embryos have reduced numbers of Rohon-Beard sensory neurons and reduced expression of prdm1a, suggesting that ap-2 genes may be more of a neural plate border specifier in zebrafish.…”

Dissecting early regulatory relationships in the lamprey neural crest gene network

“…For example, it is clear that induction of Msx1 and Zic1/Pax3/7 represent independent events in the frog (3,4,22). Although classified as neural crest specifier genes, c-Myc, Id, and AP-2 are first deployed at the neural plate border of the early neurula, rather than in nascent neural crest cells (23)(24)(25)(26)(27)(28)(29). Because recent studies suggest that onset of neural crest formation and specifier expression in both frog and chick may occur in the gastrula, these genes may act earlier in neural crest specification than formerly assumed.…”

“…Conversely, studies of AP-2 mutants in zebrafish failed to demonstrate an early role for this gene in neural crest specification, as various AP-2 mutants exhibit no change in neural crest specifier expression during early steps of neural crest formation. However, they do show defects in specific subsets of neural crest derivatives (27,29,33). The absence of early defects could be caused by compensation by redundant paralogs, endogenously coexpressed with the mutated gene, suggesting all relevant copies of AP-2 gene should be inactivated in zebrafish to replicate the AP-2 mutant phenotype observed in other vertebrates (34).…”