Initiation mechanism of the zygotic gene expression in Xenopus mid-blastula embryo

自纽波特和Kirschners（1987）提出的模型以来，究竟是什么样的母体因素控制着中囊胚的转变一直是个未知数。在这里，为了研究合子基因表达的起始机制，我们试图分离一种新的转录调节因子，该因子在原肠胚形成前已经表达并参与合子基因表达的调节。通过筛选显示母体基因表达的cDNA，我们分离了几个新基因。Xoom编码的跨膜蛋白与肌动蛋白丝的聚合密切相关，在原肠胚的形态发生运动中发挥作用。香菇编码的一种新的POZ/锌指转录因子通过细胞外基质的产生参与形态发生调控。XEXTI在卵子发生过程中表现出活跃的基因表达，在细胞外基质的产生中也发挥了作用。Notch相关分子与合子期基因表达无直接关系，而与原肠胚早期基因表达密切相关。在这项研究中，我们克隆了X-Serrate-1，它编码的Notch配体之一。X-Serrate-1、X-Notch-1、Xsu（H）基因在卵子发生至蝌蚪发育过程中普遍表达。目的基因ESR 1的基因表达表明，这些Notch相关分子在早期原肠胚中是有功能的，但在MBT之前可能通过抑制Presenilin的酶活性来阻断信号通路。功能缺失实验表明，Xsu（H）介导的转录调控对合子基因的表达是必不可少的。

Since Newport and Kirschners' model (1987), it has been remained unknown what maternal factor controls the Mid-blastula transition. Here, in order to examine the initiation mechanism of the zygotic gene expression, we have tried to isolate a novel transcriptional regulator that has been expressed maternally and participates in the regulation of the zygotic gene expression prior to gastrulation. By screening the cDNAs that show maternal gene expression, we have isolated several novel genes. Xoom encoded the transmembrane protein that has a close relation to the polymerization of actin filament, and played a role in morphogenetic movement of gastrula embryo. A novel POZ/Zinc-finger transcription factor encoded by Champignon participated in the morphogenetic regulation through the production of the extracellular matrix. XEXTI, showing active gene expression during the oogenesis, also played a role in the production of the extracellular matrix. In contrast to these molecules showing no direct relation to the zygotic gene expression, Notch-related molecules had close relation to the gene expression in the early stage of gastrula embryo. In this study, we have cloned X-Serrate-1, which encodes one of the Notch ligand. X-Serrate-1, X-Notch-1, Xsu(H) showed ubiquitous gene expression from oogenesis to tadpole stage of development. Gene expression of the target gene, ESR1, demonstrated that these Notch-related molecules are functional in the early gastrula embryo, but the signaling passway is blocked before MBT probably by inhibiting the enzyme activity of Presenilin. Loss of function experiment showed that Xsu(H)-mediated transcriptional regulation is essential to the zygotic gene expression.