The embryonic expression patterns of two additional members of the transcription factor TFAP2 family in Xenopus laevis, TFAP2beta and TFAP2gamma, are described. Both genes share overlapping expression domains with the previously characterized TFAP2alpha in this species, although differences exist. All three genes are expressed in the neural crest (NC) region at late gastrula to early neurula stages. TFAP2alpha and TFAP2gamma are also expressed in outer, epidermal cells, while TFAP2beta is essentially NC-specific. All three are induced by Wnt/beta-catenin -- BMP signals and all bind to a consensus TFAP2 recognition site from an epidermal keratin gene.
"The initial expression of two other non-neural ectoderm genes also appear to play critical roles in specifying the PPR in Xenopus: TFAP2α and Foxi1a/b (Matsuo-Takasaki et al., 2005; Luo et al., 2002; Zhang et al., 2006). Knock-down of Foxi1a/b causes expansion of neural plate genes and reduction of NB zone and epidermal genes, whereas gain-of-function reduces both neural plate and NB zone genes and expands epidermal genes (Matsuo-Takasaki et al., 2005). "
[Show abstract][Hide abstract] ABSTRACT: Specialized sensory organs in the vertebrate head originate from thickenings in the embryonic ectoderm called cranial sensory placodes. These placodes, as well as the neural crest, arise from a zone of ectoderm that borders the neural plate. This zone separates into a precursor field for the neural crest that lies adjacent to the neural plate, and a precursor field for the placodes, called the pre-placodal region (PPR), that lies lateral to the neural crest. The neural crest domain and the PPR are established in response to signaling events mediated by BMPs, FGFs and Wnts, which differentially activate transcription factors in these territories. In the PPR, members of the Six and Eya families, act in part to repress neural crest specific transcription factors, thus solidifying a placode developmental program. Subsequently, in response to environmental cues the PPR is further subdivided into placodal territories with distinct characteristics, each expressing a specific repertoire of transcription factors that provides the necessary information for their progression to mature sensory organs. In this review we summarize recent advances in the characterization of the signaling molecules and transcriptional effectors that regulate PPR specification and its subdivision into placodal domains with distinct identities.
"Increasing evidence suggests that Tfap2 proteins promote NC development both directly, through transcriptional regulation of genes like hoxa2 and ckit , as well as indirectly through signals from the epidermis. As stated above, zebrafish tfap2b is not expressed in NC cells (Moser et al., '95; Zhang et al., 2006). Instead, expression is restricted to the pharyngeal ectoderm after NC migration, where it is required to induce NC cells to form the pharyngeal skeleton (Knight et al., 2005). "
[Show abstract][Hide abstract] ABSTRACT: Transcription factor AP2 (Tfap2) genes play essential roles in development of the epidermis and migratory cells of the neural crest (NC) in vertebrate embryos. These transcriptional activators are among the earliest genes expressed in the ectoderm and specify fates within the epidermis/crest through both direct and indirect mechanisms. The Tfap2 family arose from a single ancestral gene in a chordate ancestor that underwent gene duplication to give up to five family members in living vertebrates. This coincided with the acquisition of important roles in NC development by Tfap2 genes suggesting that this gene family was important in ectodermal evolution and possibly in the origin of NC. Here, we show that a zebrafish tfap2c is expressed in the nonneural ectoderm during early development and functions redundantly with tfap2a in NC specification. In zebrafish embryos depleted of both tfap2a and tfap2c, NC cells are virtually eliminated. Cell transplantation experiments indicate that tfap2c functions cell-autonomously in NC specification. Cells of the enveloping layer, which forms a temporary skin layer surrounding the ectoderm, also fail to differentiate or to express appropriate keratins in tfap2c deficient embryos. The role of Tfap2 genes in epidermal and NC development is considered here in the broader context of ectodermal evolution. Distinct, tissue-specific functions for Tfap2 genes in different vertebrates may reflect subfunctionalisation of an ancestral gene that consequently led to the gain of novel roles for different subfamily members in patterning the epidermis and NC.
Journal of Experimental Zoology Part B Molecular and Developmental Evolution 09/2007; 308(5):679-91. DOI:10.1002/jez.b.21189 · 2.31 Impact Factor
Lautaro D Álvarez, M Virginia Dansey, Diego Y Grinman, Daniela Navalesi, Gisela A Samaja, M Celeste Del Fueyo, Niek Bastiaensen, René Houtman, Darío A Estrin, Adriana S Veleiro, Adali Pecci, Gerardo Burton
Heping Xu, Virendra K Chaudhri, Zhiguo Wu, Konstantinos Biliouris, Krista Dienger-Stambaugh, Yrina Rochman, Harinder Singh
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