Molecular mechanisms regulating optic fissure closure

眼睛的发育是一个复杂的过程，从眼场的定义到视泡的外溢和神经视网膜的分化。晶状体诱导后，视网膜背侧与其前部和后部一起向腹侧伸展和折叠。在这些后半部分交汇的区域，可以看到一条视裂。在正常发育过程中，这个视裂只是暂时存在的。裂隙通过视网膜部分的前缘和后缘融合而闭合。视裂闭合缺陷，称为缺损，可影响几个眼结构，如虹膜、脉络膜或视网膜，并可合并中枢神经系统(CNS)其他部分以及其他器官(如心脏和肾脏)的畸形。在受影响的患者和小鼠中发现的基因突变导致了缺陷基因调控网络的提出。尽管已经鉴定出许多基因，主要是转录因子，如果改变会导致缺陷症的形成，但与调节这一过程的效应分子的联系仍然难以捉摸。从我们的初步工作中我们知道，除了已经描述的眼睛发育的许多缺陷外，转化生长因子-β2的丢失还会导致缺乏视裂闭合和过度细胞的、无组织的视网膜。转化生长因子β是一类调节细胞增殖、分化、存活和死亡的细胞外介质家族。该项目的具体目的是揭开细胞外分子如转化生长因子-β如何协调视裂闭合以及转化生长因子-β依赖的信号如何整合到已知的缺陷基因网络中的分子和机制细节。该项目是由两个在鱼类和老鼠视网膜发育方面拥有独特专业知识的实验室共同努力的。该项目将首先利用转化生长因子-β2基因缺失的小鼠对潜在的转化生长因子-β靶基因进行系统分析，并与E13.5(视裂闭合前)和E16.5(神经视网膜的增殖和分化)的野生型小鼠进行比较，然后进行适当的生物信息学处理和数据库分析。对候选基因的功能分析将在FISH中完成。此外，还将建立一种缺乏转化生长因子-β信号的视网膜特异性小鼠系(CRE-Rx3 x TBR-IIflx/FLOX)，以研究转化生长因子-β诱导的视网膜发育，而不依赖于间充质来源的转化生长因子-β信号。

Eye development is an intricate process, ranging from the definition of the eye field, to optic vesicle evagination and differentiation of the neuroretina. After lens induction the dorsal retinal anlage extends and folds ventrally with its anterior and posterior parts. In the area where these latter parts will meet, an optic fissure is visible. During normal development, this optic fissure is only transiently present. The fissure closes by fusion of the anterior and posterior edges of the retinal parts. Defects of optic fissure closure, referred to as coloboma, can affect several eye structures like iris, choroidea or retina and may be combined with malformations of other parts of the central nervous system (CNS), and also other organs (i.e. heart and kidney). Gene mutations identified in affected patients as well as in mice have led to the proposal of a coloboma gene regulatory network. Although many genes, primarily transcription factors that lead to coloboma formation if altered have been identified, the link to effector molecules mediating the process is still elusive. From our preliminary work we know that loss of TGF-beta2 leads, in addition to numerous already described defects in eye development, to a lack of optic fissure closure and a hypercellular, disorganized retina. TGF-betas are a family of extracellular mediators regulating cell proliferation, differentiation, survival and death. The specific aim of the proposed project is to unravel the molecular and mechanistic details of how extracellular molecules such as TGF-beta orchestrate optic fissure closure and how TGF-beta dependent signaling integrates into the known coloboma gene network. The project is a joint effort of two laboratories with unique expertise in retina development in fish and mouse. The project will start by a systematic analysis of potential TGF-beta target genes using TGF-beta2 null mice in comparison to wild type litter mates at E13.5 (before optic fissure closure) and E16.5 (proliferation and differentiation of neuroretina), followed by appropriate bioinformatics processing and database analyses. Functional analysis of candidate genes will be done in fish. Furthermore, a retina-specific mouse line lacking TGF-beta signaling (Cre-Rx3 x TbR-IIflox/flox) will be generated to study TGF-beta induced retina development independent of mesenchyme-derived TGF-beta signaling.