鉴定脑前嵴外胚层和感觉器官发育的早期需求。
Identification of early requirements for preplacodal ectoderm and sensory organ development.
机构信息
Biology Department, Texas A&M University, College Station, Texas, United States of America.
出版信息
PLoS Genet. 2010 Sep 23;6(9):e1001133. doi: 10.1371/journal.pgen.1001133.
Preplacodal ectoderm arises near the end of gastrulation as a narrow band of cells surrounding the anterior neural plate. This domain later resolves into discrete cranial placodes that, together with neural crest, produce paired sensory structures of the head. Unlike the better-characterized neural crest, little is known about early regulation of preplacodal development. Classical models of ectodermal patterning posit that preplacodal identity is specified by readout of a discrete level of Bmp signaling along a DV gradient. More recent studies indicate that Bmp-antagonists are critical for promoting preplacodal development. However, it is unclear whether Bmp-antagonists establish the proper level of Bmp signaling within a morphogen gradient or, alternatively, block Bmp altogether. To begin addressing these issues, we treated zebrafish embryos with a pharmacological inhibitor of Bmp, sometimes combined with heat shock-induction of Chordin and dominant-negative Bmp receptor, to fully block Bmp signaling at various developmental stages. We find that preplacodal development occurs in two phases with opposing Bmp requirements. Initially, Bmp is required before gastrulation to co-induce four transcription factors, Tfap2a, Tfap2c, Foxi1, and Gata3, which establish preplacodal competence throughout the nonneural ectoderm. Subsequently, Bmp must be fully blocked in late gastrulation by dorsally expressed Bmp-antagonists, together with dorsally expressed Fgf and Pdgf, to specify preplacodal identity within competent cells abutting the neural plate. Localized ventral misexpression of Fgf8 and Chordin can activate ectopic preplacodal development anywhere within the zone of competence, whereas dorsal misexpression of one or more competence factors can activate ectopic preplacodal development in the neural plate. Conversely, morpholino-knockdown of competence factors specifically ablates preplacodal development. Our work supports a relatively simple two-step model that traces regulation of preplacodal development to late blastula stage, resolves two distinct phases of Bmp dependence, and identifies the main factors required for preplacodal competence and specification.
神经褶前外胚层起源于原肠胚晚期,作为一个环绕前神经板的细胞窄带。这个区域后来分化为离散的颅嵴基板,与神经嵴一起产生头部的成对感觉结构。与更好表征的神经嵴不同,早期调控神经褶前外胚层发育的机制知之甚少。经典的外胚层模式形成模型认为,神经褶前外胚层的身份是通过沿 DV 梯度读取离散水平的 Bmp 信号来指定的。最近的研究表明,Bmp 拮抗剂对于促进神经褶前外胚层的发育至关重要。然而,尚不清楚 Bmp 拮抗剂是在形态发生素梯度内建立适当的 Bmp 信号水平,还是完全阻断 Bmp。为了开始解决这些问题,我们用 Bmp 的药理学抑制剂处理斑马鱼胚胎,有时与 Chordin 和显性负性 Bmp 受体的热休克诱导相结合,以在各种发育阶段完全阻断 Bmp 信号。我们发现神经褶前外胚层的发育分为两个阶段,需要相反的 Bmp 要求。最初,在原肠胚形成之前,Bmp 是必需的,以共同诱导四个转录因子,Tfap2a、Tfap2c、Foxi1 和 Gata3,它们在整个非神经外胚层中建立神经褶前外胚层的能力。随后,在晚期原肠胚形成时,需要通过背侧表达的 Bmp 拮抗剂与背侧表达的 Fgf 和 Pdgf 一起完全阻断 Bmp,以在与神经板相邻的有能力的细胞中指定神经褶前外胚层的身份。局部腹侧异位表达 Fgf8 和 Chordin 可以在能力区域内的任何地方激活异位神经褶前外胚层的发育,而一个或多个能力因子的背侧异位表达可以在神经板中激活异位神经褶前外胚层的发育。相反,能力因子的 morpholino 敲低特异性地消除了神经褶前外胚层的发育。我们的工作支持一个相对简单的两步模型,该模型将神经褶前外胚层发育的调控追溯到晚期囊胚阶段,确定了两个不同的 Bmp 依赖性阶段,并确定了神经褶前外胚层能力和指定所需的主要因素。