Hedgehog Signaling Coordinates Stochastic and Stereotyped Patterns in the Drosophila Eye

项目摘要 有机体的发育需要定型和随机模式。定型模式 在个体之间产生几乎相同的结构。相反，随机细胞命运规范 产生了每个人都独特的随机模式。随机的命运决定是必要的， 许多感觉器官的发育，包括视觉和嗅觉系统。尽管它们很重要， 控制定型和随机模式在同一组织内交叉的分子机制还没有 已经解决了。该项目旨在确定基因调控机制是如何调整的，以产生高水平的 使用果蝇眼睛作为模型，在同一组织中的规则模式和随机模式。 果蝇的眼睛由大约800个小眼组成，排列近乎完美。每个小眼包括 八个光感受器（R1-8），以可预测的方式发育。当光感受器在 在幼虫眼睛发育过程中，由Hedgehog（Hh）信号驱动的形态发生波驱动了眼睛的高度发育。 眼睛的可复制结构。在蝇眼的均匀形态下是一种随机的模式， 光感受器亚型两种R7感光细胞亚型通过光检测视紫红质的表达来定义 proteins.这两种R7亚型的随机模式化由以下基因的随机ON/OFF表达控制： 转录因子，无脊椎（Ss）。SsON R7表达视紫红质4（Rh 4），而SsOFF R7表达 视紫红质3（Rh 3）。ss是由转录和染色质调控的相互作用， 发展 我发现Hh信号在眼睛发育中起着调节随机模式的第二个作用。hh 突变体显示SsON R7的百分比降低。Cubitus Interruptus（Ci），Hh信号传导的效应子， 结合在SS中的眼特异性增强子上。该位点与Klumpfuss（Klu）的结合位点重叠，Klumpfuss（Klu）是 ss，表明竞争性约束和监管。 我假设Hh信号被精细调节以驱动刻板的眼睛模式并诱导ss 在前体中转录以产生随机R7亚型模式。我将通过以下方式来检验这个假设：1） 确定Hh通路如何调节随机ss表达，2）描述Hh通路如何与 Ci和Klu调节ss表达，以及3）确定Hh信号传导和染色质调节如何整合 在ss位点。总之，这些实验将提供第一次分析的协调之间的随机 和单一组织内的定型基因表达，并将增强我们对 随机细胞命运规范。

Project Summary Development of an organism requires both stereotyped and stochastic patterning. Stereotyped patterning robustly generates nearly identical structures across individuals. In contrast, stochastic cell fate specification produces randomized patterns that are unique to each individual. Stochastic fate decisions are required for the development of many sensory organs, including visual and olfactory systems. Despite their importance, how the molecular mechanisms controlling stereotyped and random patterns intersect within the same tissue has not been addressed. This project aims to determine how gene regulatory mechanisms are tuned to generate highly regular patterns and stochastic patterns in the same tissue using the Drosophila eye as a model. The Drosophila eye is composed of ~800 ommatidia in a near perfect array. Each ommatidium comprises eight photoreceptors (R1-8) which develop in a predictable fashion. As photoreceptors are differentiating during larval eye development, a wave of morphogenesis driven by Hedgehog (Hh) signaling drives the highly reproducible structure of the eye. Underlying the uniform morphology of the fly eye is a random pattern of photoreceptor subtypes. Two R7 photoreceptor subtypes are defined by expression of light-detecting Rhodopsin proteins. Random patterning of these two R7 subtypes is controlled by stochastic ON/OFF expression of the transcription factor, Spineless (Ss). SsON R7s express Rhodopsin 4 (Rh4), whereas SsOFF R7s express Rhodopsin 3 (Rh3). ss is regulated by an interplay of transcription and chromatin regulation during larval eye development. I found that Hh signaling plays a second role in eye development to regulate stochastic patterning. hh mutants display a reduction in the percentage of SsON R7s. Cubitus Interruptus (Ci), an effector of Hh signaling, binds at an eye specific enhancer in ss. This site overlaps with a binding site for Klumpfuss (Klu), a repressor of ss, suggesting competitive binding and regulation. I hypothesize that Hh signaling is finely tuned to drive stereotyped eye patterning and induce ss transcription in precursors to generate stochastic R7 subtype patterning. I will test this hypothesis by 1) Determining how the Hh pathway regulates stochastic ss expression, 2) Describing how antagonism between Ci and Klu regulates ss expression, and 3) Determining how Hh signaling and chromatin regulation are integrated at the ss locus. Together, these experiments will provide the first analysis of coordination between stochastic and stereotyped gene expression within a single tissue and will enhance our mechanistic understanding of stochastic cell fate specification.