Ectoderm formation in the early Xenopus embryo

描述（由申请方提供）：形态发生的基本组成部分之一是细胞相互分离以形成新组织或器官的能力。 在脊椎动物发育过程中，最早的例子是初级胚层的形成。 在非洲爪蟾中，每个胚层都来自球形囊胚的一个单独区域。 外胚层来自动物细胞，中胚层来自边缘细胞，内胚层来自植物细胞。 谱系分析，区域标记的表达，组织重组实验，细胞分选实验和细胞移植实验都表明，规范的胚层发生在中期至晚期囊胚阶段，在明显分离的胚层。 植物细胞遗传了一种母系编码的转录因子VegT。 这激活了启动内胚层分化的其他转录因子的表达，以及诱导相邻边缘区细胞形成中胚层的信号分子。 导致外胚层形成的途径尚不清楚。 初步数据表明，它也是由卵母细胞中转录的mRNA启动的，并由卵子遗传。 我们已经发现，已知仅在外胚层中表达的LIM同源结构域蛋白XLIM 5是母体转录因子的直接靶标，并且当在早期植物细胞中过度表达时，导致其后代分离到其他胚层。 本项目的目标是以此为起点，以确定导致外胚层特化和动物细胞分离形成外胚层的途径。 我们将确定激活XLIM 5表达的上游母体因子，以及赋予动物细胞外胚层型粘附的下游基因，并通过简单的功能获得和丧失测定来测试它们的个体功能。 我们还将研究外胚层和内胚层途径之间的相互作用，导致在囊胚阶段的差异粘附行为。

DESCRIPTION (provided by applicant): One of the fundamental components of morphogenesis is the ability of cells to segregate from each other to form new tissues or organs. The earliest example of this during vertebrate development is the formation of the primary germ layers. In Xenopus, each germ layer arises from a separate area of the spherical blastula. The ectoderm arises from animal cells, the mesoderm from marginal cells, and the endoderm from vegetal cells. Lineage analysis, the expression of regional markers, tissue recombination experiments, cell sorting experiments, and cell transplantation experiments all suggest that specification of the germ layers occurs during the mid- to late-blastula stages, before overt segregation of the germ layers. Vegetal cells inherit a maternally encoded transcription factor, VegT. This activates the expression of other transcription factors that initiate endoderm differentiation, and signaling molecules that induce the neighboring marginal zone cells to form mesoderm. The pathway leading to ectoderm formation is unknown. Preliminary data suggests that it is also initiated by mRNAs transcribed in the oocyte and inherited by the egg. We have found that a LIM homeodomain protein, XLIM5, already known to be expressed only in the ectoderm, is an immediate target of maternal transcription factor(s), and, when over expressed in early vegetal cells, causes their descendants to segregate to other germ layers. The goals of this project are to use this as a starting point to identify the pathway leading to ectoderm specification and the segregation of animal cells to form the ectoderm germ layer. We will identify the upstream maternal factors that activate XLIM5 expression, and the downstream genes which confer ectoderm-type adhesion on animal cells, and test their individual functions by simple gain- and loss-of function assays. We will also investigate the interaction between the ectoderm and endoderm pathways that leads to differential adhesion behaviour at the blastula stage.