Differential Response to the Dpp Morphogen

描述（由申请人提供）：在所有动物中，胚胎发生的初始事件是由母体基因产物控制的，这些基因产物沉积在发育中的卵母细胞中。在受精后的某一时刻，胚胎发生的控制权被转移到合子基因组，这一过程被称为母体到合子过渡（MZT）。在此期间，母体rna被降解，合子rna被转录。尽管在RNA降解机制方面取得了进展（Giraldez等人，2006），但合子基因组的激活因子仍然难以捉摸。许多果蝇合子基因共享一个与CAGGTAG相关的顺式调控基序（ten Bosch et al.,2006; De Renzis et al., 2007），这一发现提供了线索。我们最近分离出一种锌指蛋白，Zelda，它专门与这些位点结合。缺乏母系zelda转录本的突变胚胎不能激活合子基因样本的转录，并且在细胞化过程的几个方面存在缺陷，这相当于胚胎不能再仅靠母系产物存活（Merrill et al., 1988）。我们的初步结果表明，Zelda在MZT期间激活了一系列基因，每个基因负责一个关键的发育过程。Zelda可能激活介导母体RNA降解的早期转录microrna，从而在MZT的两个标志性事件之间提供联系。基于我们的初步数据，我们将进一步描述塞尔达在MZT中的角色。塞尔达激活了多少基因，哪些早期基因与塞尔达无关？我们将在Aim 1中使用基因组学方法来确定早期胚胎中的所有Zelda靶点。《塞尔达传说》激活了多少基因，是否有不受《塞尔达传说》调节的基因群？在目标2中，我们询问Zelda在激活靶基因方面是否发挥指导或许可作用，或者两者兼有，以及它如何与其他关键调节因子（如Dorsal和Dpp）相互作用以激活其靶基因。在Aim 3中，我们研究了保守的Zelda蛋白结构域的结构和功能，并测试了Zelda功能是否在长胚芽黄蜂中存在，以及它是否在激活合子基因组中起类似的作用。最后，我们解决了关于Aim 4中基因组激活时间的机制问题，以及Zelda在逆转基因组初始沉默中的可能作用。本提案中概述的实验有可能极大地促进我们对MZT背后机制的理解。

DESCRIPTION (provided by applicant): In all animals the initial events of embryogenesis are controlled by maternal gene products that are deposited into the developing oocyte. At some point after fertilization, control of embryogenesis is transferred to the zygotic genome in a process called the maternal to zygotic transition (MZT). During this time maternal RNAs are degraded and zygotic RNAs are transcribed. Although progress has been made on the mechanisms underlying RNA degradation (Giraldez et al., 2006), the activators of the zygotic genome have remained elusive. A hint came from the discovery that many Drosophila zygotic genes share a cis-regulatory motif related to CAGGTAG (ten Bosch et al.,2006; De Renzis et al., 2007). We recently isolated a zinc-finger protein, Zelda, which binds specifically to these sites. Mutant embryos lacking maternal zelda transcripts fail to activate the transcription of a sample of zygotic genes, and are defective in several aspects of the cellularization process, which corresponds to the point at which embryos can no longer survive on maternal products alone (Merrill et al., 1988). Our preliminary results suggest that Zelda activates batteries of genes during the MZT, each responsible for a key developmental process. Zelda may activate early-transcribed microRNAs that mediate maternal RNA degradation, thus providing a link between the two hallmark events of the MZT. Building on our preliminary data, we will further characterize the role of Zelda in the MZT. How many genes does Zelda activate and which early genes are independent of Zelda? We will use a genomics approach in Aim 1 to determine all Zelda targets in the early embryo. How many genes does Zelda activate, and are there groups of genes not regulated by Zelda? In Aim 2 we ask whether Zelda plays an instructive or permissive role, or both, in activating target genes, and how it interacts with other key regulators such as Dorsal and Dpp to activate their target genes. In Aim 3 we investigate the structure and function of conserved Zelda protein domains, and test whether there is Zelda function in the long germ Nasonia wasp and if it plays a similar role in activating the zygotic genome. Finally, we address mechanistic questions regarding the timing of genome activation in Aim 4, and the possible role of Zelda in reversing the initial silencing of the genome. The experiments outlined in this proposal have the potential to advance greatly our understanding of the mechanisms underlying the MZT. PUBLIC HEALTH RELEVANCE: The study of the molecular mechanisms underlying basic developmental processes is relevant to understanding the cause and progression of human diseases such as cancer, and human disorders such as birth defects.