F-box蛋白和Torso/MAPK通路在果蝇胚胎前后端发育中的调控作用

Mechanistic understanding of human genetic disorders that cause birth defects requires fundamental knowledge of both the sensitive and robust aspects of developmental processes. The proposed work seeks to dissect the intricate regulatory network controlling embryonic pattern formation at a quantitative, systems level. The morphogen concept is central to developmental biology. Morphogen molecules form concentration gradients to provide positional information to a field of cells. We propose to perform quantitative studies to dissect the molecular mechanisms of anterior-posterior (AP) patterning controlled by the morphogen gradient of Bicoid (Bcd) and excecuted by the gap gene regulatory network in the Drosophila embryo. The overall hypothesis of this application is that a multi-layered regulatory network enables Bcd to respond to, and interact with, various other regulatory inputs to control the dynamics of pattern formation. These layers of regulation are both before and during the time of gradient formation, and at the time of its action as a transcriptional activator. We will study the mechanisms that regulate Bcd gradient formation by focusing on the roles of F-box proteins and the MAP kinase (MAPK) pathway. We will also investigate the mechanisms that regulate the action of Bcd as a transcriptional activator by focusing on its interaction with F-box proteins and the MAPK pathway and the roles of post-translational modifications. We will also investigate the mechanistic origins of the formation of a Bcd gradient and its regulatory consequences by unifying the results of three distinct evolutionary scales: within-population, within-species and between-species. The proposed study is based on strong preliminary studies and is made possible by a set of quantitative tools recently established in our lab. It will have powerful and sustained impact on our efforts to understand how morphogen gradients work and how developmental robustness is achieved.

成形素和基因调控网络是发育生物学的两个核心概念。成形素蛋白分子形成浓度梯度给特定区域的细胞提供基因表达、分化和发育的位置信息，基因调控网络整合来自上游的位置信息从而形成特定的表达模式。以定量和系统地解析胚胎前后轴线上发育模式建立的调控机制为目标，本项目拟从三个层次全面阐释果蝇早期胚胎中Bicoid转录调控系统：1.F-box蛋白和Torso/MAPK信号通路在Bicoid蛋白梯度形成中的功能；2.这些因子对Bicoid转录因子活性的影响；3.构建Bicoid梯度介导的调控网络的在群体内、物种内和物种间不同水平的演化模型。应用一系列体内外的实验手段，本项目将整合上游蛋白质修饰和调节信号的数据、Bicoid动态变化的数据和下游间隙基因相互作用的数据，剖析胚胎发育模式的鲁棒性和尺度性的基本生物学问题。

发育鲁棒性是发育生物学中的一个根本问题。作为该现象的重要特征之一，发育中的组织器官如何形成与其尺寸大小成比例的模式图案仍然是一个亟待解决的问题。目前国际上对此争论的热点主要在于，组织或胚胎的早期发育中指引模式形成的形态发生素梯度，是否编码了与尺寸大小成比例的精确位置信息，能否在发育过程中发挥持续性的控制作用。.本项目以早期果蝇胚胎前后轴（AP轴）发育为模式系统，利用长度和Bicoid成形素梯度尺度性特征存在显著差异的胚胎（4个品系，总计超过5000只胚胎，跨越10个精细的早期胚胎发育阶段），来进一步调查下游间隙基因的时空表达模式。这种胚胎长度差异要比正常情况下的自然变异大10倍以上，使特异性和敏感性地探究与胚胎长度和上游Bicoid输入相关的间隙基因表达模式的缩放特性，能够成为可能。该研究系统地分析了在应对胚胎长度和Bicoid输入的变异时，间隙基因表达边界随着时间沿着头尾轴的动态移动，并展现了这种动态移动是如何推动全局缩放模式的形成，以及基因表达边界特定缩放特征的演变过程。分析结果表明，尽管初始的Bicoid梯度的模式缩放特征存在差异，但最终的缩放模式特征会收敛，这一现象反映了发育模式的鲁棒性。本项研究有效地划分了Bicoid的上游输入调控和AP模式网络固有的调节动力在塑造胚胎发育模式的尺度性特征方面的贡献。这些结果为深入理解发育模式形成的形态素调控机制和一般性物化规律提供了范式研究和重要线索，部分结果已发表。