Neural crest survival and differentiation in zebrafish depends onmont blanc/tfap2agene function

Abstract

Neural crest progenitor cells are the main contributors to craniofacial cartilage and connective tissue of the vertebrate head. These progenitor cells also give rise to the pigment, neuronal and glial cell lineages. To study the molecular basis of neural crest differentiation, we have cloned the gene disrupted in the mont blanc (mobm610) mutation,which affects all neural crest derivatives. Using a positional candidate cloning approach we identified an A to G transition within the 3′ splice site of the sixth intron of the tfap2a gene that abolishes the last exon encoding the crucial protein dimerization and DNA-binding domains. Neural crest induction and specification are not hindered in mobm610 mutant embryos, as revealed by normal expression of early neural crest specific genes such as snail2, foxd3and sox10. In addition, the initial stages of cranial neural crest migration appear undisturbed, while at a later phase the craniofacial primordia in pharyngeal arches two to seven fail to express their typical set of genes (sox9a, wnt5a, dlx2, hoxa2/b2). In mobm610 mutant embryos, the cell number of neuronal and glial derivatives of neural crest is greatly reduced, suggesting that tfap2a is required for their normal development. By tracing the fate of neural crest progenitors in live mont blanc(mobm610) embryos, we found that at 24 hpf neural crest cells migrate normally in the first pharyngeal arch while the preotic and postotic neural crest cells begin migration but fail to descend to the pharyngeal region of the head. TUNEL assay and Acridine Orange staining revealed that in the absence of tfap2a a subset of neural crest cells are unable to undergo terminal differentiation and die by apoptosis. Furthermore, surviving neural crest cells in tfap2a/mobm610 mutant embryos proliferate normally and later differentiate to individual derivatives. Our results indicate that tfap2a is essential to turn on the normal developmental program in arches 2-7 and in trunk neural crest. Thus, tfap2a does not appear to be involved in early specification and cell proliferation of neural crest, but it is a key regulator of an early differentiation phase and is required for cell survival in neural crest derived cell lineages.

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.…”

The mother superior mutation ablates foxd3 activity in neural crest progenitor cells and depletes neural crest derivatives in zebrafish

“…To examine possible defects in neuronal derivatives, we marked trunk neurons using a pan-neuronal monoclonal antibody against the HuC/HuD protein (Barrallo-Gimeno et al, 2004). The Dorsal Root Ganglia (DRGs) of wild-type embryos, providing sensory innervation to the trunk region, are located bilaterally in each somitic segment at the level of the ventral neural tube (Fig.…”

How to become neural crest: From segregation to delamination

“…At differentiation stages, AP-2α participates in the generation of diverse neural crest derivatives including pigment cells, sensory neurons and cartilage (HilgerEversheim et al, 2000;Knight et al, 2003;Barrallo-Gimeno et al, 2004). However, AP-2α is initially expressed throughout the ectoderm, suggesting that other factors must be involved in restricting neural crest induction to the appropriate region.…”

“…Interestingly, zebrafish embryos lacking Sox9b, the Sox9 gene expressed in the neural crest, display massive apoptosis in the central nervous system and the pharyngeal cartilage precursors (Yan et al, 2005). In addition to Sox9 and Snail2, AP-2α is also involved in conferring survival properties to the migratory neural crest population (Knight et al, 2003;Barrallo-Gimeno et al, 2004).…”