lockjawencodes a zebrafishtfap2arequired for early neural crest development

Abstract

The neural crest is a uniquely vertebrate cell type that gives rise to much of the craniofacial skeleton, pigment cells and peripheral nervous system, yet its specification and diversification during embryogenesis are poorly understood. Zebrafish homozygous for the lockjaw (low)mutation show defects in all of these derivatives and we show that low (allelic with montblanc) encodes a zebrafish tfap2a, one of a small family of transcription factors implicated in epidermal and neural crest development. A point mutation in lowtruncates the DNA binding and dimerization domains of tfap2a, causing a loss of function. Consistent with this, injection of antisense morpholino oligonucleotides directed against splice sites in tfap2a into wild-type embryos produces a phenotype identical to low. Analysis of early ectodermal markers revealed that neural crest specification and migration are disrupted in low mutant embryos. TUNEL labeling of dying cells in mutants revealed a transient period of apoptosis in crest cells prior to and during their migration. In the cranial neural crest, gene expression in the mandibular arch is unaffected in low mutants, in contrast to the hyoid arch, which shows severe reductions in dlx2 and hoxa2 expression. Mosaic analysis, using cell transplantation,demonstrated that neural crest defects in low are cell autonomous and secondarily cause disruptions in surrounding mesoderm. These studies demonstrate that low is required for early steps in neural crest development and suggest that tfap2a is essential for the survival of a subset of neural crest derivatives.

Analysis of opo cis-regulatory landscape uncovers Vsx2 requirement in early eye morphogenesis

“…The fact that opo and tfap2a are not separated by CTCF-binding sites and that they are both contained within the same topologically associating domain 51 open the possibility that common cis-regulatory elements may coregulate these two genes. Indeed, opo and tfap2a may constitute a small synexpression cluster in the genome, given their common expression in neural crest derivatives and their role in craniofacial development 28,52 . Here we have used a combination of phylogenetic footprinting and predictive epigenetic marks to identify candidate cis-regulatory regions (that is, CNEs and active enhancers, respectively), which were then functionally tested in transgenesis assays in zebrafish.…”

Ubc9 Regulates Mitosis and Cell Survival during Zebrafish Development

“…At their final locations, neural crest cells interact with cells of the pharyngeal ectoderm and endoderm that form the pouch-like structures, separating the different crest streams and surrounding the later arches, as well as with noncrest derived mesenchymal cells to finally form the seven distinct pharyngeal arches (Schilling and Kimmel, 1994;Miller et al, 2000;Piotrowski and Nü sslein-Volhard, 2000). Defective arch formation can therefore be caused by defects in the cranial neural crest population before, during, or after their migration (Yan et al, 2002;Knight et al, 2003), as well as by defects in pharyngeal pouch endoderm, ectoderm, or mesenchyme, which supply trophic support to the developing chondrocytes (Miller et al, 2000;Piotrowski and Nusslein-Volhard, 2000;David et al, 2002).…”

Frontal nasal prominence expression driven by Tcfap2a relies on a conserved binding site for STAT proteins

“…The human gene encoding AP-2␣, TFAP2A, maps in close proximity to a region of chromosome 6p24 that is frequently involved in translocations and deletions associated with orofacial clefting (Davies et al, 1999a(Davies et al, ,b, 2004Topping et al, 2002;Schultz et al, 2004), raising the possibility that alterations in the long-range cis-regulatory sequences controlling TFAP2A expression might be responsible for congenital defects affecting human facial development. In the context of evolution, evidence from multiple species indicates that changes in the spatial and temporal regulation of the AP-2 family of genes, among others, might underlie the evolution of the vertebrate neural crest and, ultimately, the diversity of craniofacial skeleton (Meulemans and BronnerFraser, 2002;Holzschuh et al, 2003;Knight et al, 2003Knight et al, , 2005Luo et al, 2003;O'Brien et al, 2004). To identify the regulatory hierarchy underlying the expression of Tcfap2a, and to determine how it might have been altered during evolution, or in human genetic disease, we have previously analyzed various species to locate regions of the gene that are responsible for driving AP-2␣ expression in different tissues (Zhang and Williams, 2003;Zhang et al, unpublished data).…”