Early activation of the zygotic genome

描述(申请人提供)：受精后，在许多生物中，胚胎基因组的激活被延迟，直到哺乳动物的合子基因激活(ZGA)和模式生物如非洲爪哇、斑马鱼和果蝇的中胚期转变(MET)。人们普遍认为，合子转录在这一关键转变之前不会发生，大多数关于早期胚胎基因表达的研究都集中在转录抑制的机制上。这个实验室已经确定了在MET之前在非洲爪哇中强健转录的基因。此外，母体转录因子，包括Wnt调节的S-连环蛋白/Tcf复合体，是前MBT转录所必需的；干扰它们的前MBT功能显著扰乱胚胎发育，包括神经管、脊索和肌肉的形成。我们已经鉴定了在前MBT胚胎中活跃的启动子序列，这在以前还没有关于非洲爪哇启动子(或常规病毒启动子，如CMV或SV40启动子)的报道。我们已经确定了与前MBT基因表达相关的特定染色质修饰，并证明了B-连环蛋白与前MBT胚胎中Wnt调节的启动子直接结合。我们将在全球转录沉默的背景下，研究选定基因在早期胚胎中被激活的机制，并研究特定的转录因子、上游调控序列和整体染色质结构如何调控前MBT转录。将确定赋予前MBT转录的特定序列，并将使用功能丧失方法来测试母体转录因子在调节前MBT转录中的作用。我们将研究母体转录因子在MBT之前和之后对活性基因启动子的访问。DNA甲基化、组蛋白修饰和核小体重塑在早期胚胎的基因沉默和激活机制中起着关键作用，这些机制的干扰会导致多系统发育缺陷，包括Rett综合征、Beckwith-Wiedeman综合征和Rubenstein-Taybi综合征。我们的数据表明，在MBT之前选择性地激活基因，以及全局抑制，对于胚胎的正常发育至关重要。这里提出的这项研究应该会为胚胎基因表达错误如何导致人类严重的发育缺陷提供见解。

DESCRIPTION (provided by applicant): Following fertilization, activation of the embryonic genome is delayed in many organisms until a major transition known as zygotic gene activation (ZGA) in mammals and the midblastula transition (MET) in model organisms such as Xenopus, zebrafish, and Drosophila. It has been widely accepted that zygotic transcription does not occur before this critical transition, and most research on gene expression in early embryos has focused on the mechanisms of transcription repression. This laboratory has identified genes that are robustly transcribed in Xenopus before the MET. Furthermore, maternal transcription factors, including the Wnt-regulated S-catenin/Tcf complex, are required for preMBT transcription; interference with their preMBT function markedly disrupts embryonic development, including formation of the neural tube, notochord, and muscle. We have identified promoter sequences that are active in preMBT embryos, which have not previously been reported for any Xenopus promoter (or for conventional viral promoters such as CMV or SV40 promoters). We have identified specific chromatin modifications associated with preMBT gene expression and have demonstrated direct binding of B-catenin to Wnt regulated promoters in preMBT embryos. We will examine the mechanisms by which selected genes are activated in early embryos, in the setting of global transcription silencing, and investigate how specific transcription factors, upstream regulatory sequences, and overall chromatin architecture regulate preMBT transcription. Specific sequences that confer preMBT transcription will be identified and loss of function approaches will be used to test the role of maternal transcription factors in regulating preMBT transcription. We will examine the access of maternal transcription factors to the promoters of genes active before vs. after the MBT. DNA methylation, histone modifications, and nucleosome remodeling play key roles in gene silencing and activation mechanisms in early embryos, and interference with these mechanisms causes multi-system developmental defects, including Rett, Beckwith-Wiedeman, and Rubenstein-Taybi syndromes. Our data suggest that selective gene activation before MBT, as well as global repression, is critical for normal development of the embryo. The research proposed here should provide insights into how errors in embryonic gene expression could cause profound developmental defects in humans.