Schlosser Gerhard, Ahrens Katja
Brain Research Institute, University of Bremen, 28334 Bremen, Germany.
Dev Biol. 2004 Jul 15;271(2):439-66. doi: 10.1016/j.ydbio.2004.04.013.
We analyzed the spatiotemporal pattern of expression of 15 transcription factors (Six1, Six4, Eya1, Sox3, Sox2, Pax6, Pax3, Pax2, Pax8, Dlx3, Msx1, FoxI1c, Tbx2, Tbx3, Xiro1) during placode development in Xenopus laevis from neural plate to late tail bud stages. Out of all genes investigated, only the expression of Eya1, Six1, and Six4 is maintained in all types of placode (except the lens) throughout embryonic development, suggesting that they may promote generic placodal properties and that their crescent-shaped expression domain surrounding the neural plate defines a panplacodal primordium from which all types of placode originate. Double-labeling procedures were employed to reveal the precise position of this panplacodal primordium relative to neural plate, neural crest, and other placodal markers. Already at neural plate stages, the panplacodal primordium is subdivided into several subregions defined by particular combinations of transcription factors allowing us to identify the approximate regions of origin of various types of placode. Whereas some types of placode were already prefigured by molecularly distinct areas at neural plate stages, the epibranchial, otic, and lateral line placodes arise from a common posterior placodal area (characterized by Pax8 and Pax2 expression) and acquire differential molecular signatures only after neural tube closure. Our findings argue for a multistep mechanism of placode induction, support a combinatorial model of placode specification, and suggest that different placodes evolved from a common placodal primordium by successive recruitment of new inducers and target genes.
我们分析了非洲爪蟾从神经板到尾芽晚期阶段基板发育过程中15种转录因子(Six1、Six4、Eya1、Sox3、Sox2、Pax6、Pax3、Pax2、Pax8、Dlx3、Msx1、FoxI1c、Tbx2、Tbx3、Xiro1)的时空表达模式。在所有研究的基因中,只有Eya1、Six1和Six4的表达在整个胚胎发育过程中在所有类型的基板(晶状体除外)中持续存在,这表明它们可能促进基板的一般特性,并且它们围绕神经板的新月形表达域定义了一个泛基板原基,所有类型的基板都起源于此。采用双重标记程序来揭示这个泛基板原基相对于神经板、神经嵴和其他基板标记的精确位置。在神经板阶段,泛基板原基就已被细分为由特定转录因子组合定义的几个亚区域,这使我们能够确定各种类型基板的大致起源区域。虽然某些类型的基板在神经板阶段就已由分子上不同的区域预先形成,但鳃后、耳和侧线基板起源于一个共同的后基板区域(以Pax8和Pax2表达为特征),并且仅在神经管闭合后才获得不同的分子特征。我们的研究结果支持基板诱导的多步骤机制,支持基板特化的组合模型,并表明不同的基板通过相继招募新的诱导因子和靶基因从一个共同的基板原基进化而来。