Nuclear Receptor and Co-Repressor Function in Eye Development

核受体复合物一直被认为是配体激活的转录因子。最近的细胞培养工作强烈表明，核受体二聚体可以对单个启动子起负性和正性作用。核受体介导的抑制依赖于核受体共抑制因子，它与无配体的核受体二聚体结合。这些共抑制因子被配体取代，去除抑制，并允许激活因子结合。为了研究核受体及其协同抑制伙伴在体内的作用，实验将以果蝇眼为实验对象，研究含rxr二聚体在细胞命运、分化和发育协调中的调节作用。为了从遗传学、发育学和分子学的角度来解决这个问题，在正常发育的背景下，实验集中在超胞囊（usp），即果蝇RXR，在控制眼内形态发生沟运动和细胞分化的早期阶段中的作用。发育中的果蝇眼睛为研究rxr介导的激活/抑制系统提供了一个很好的模型。眼原基有明显的收缩，即形成沟，将前后区分开。形态发生沟由后向前穿过原基。前区细胞未分化，没有任何特定的命运。在后侧，细胞承诺和分化以可复制和刻板的方式发生。形成沟的正常运动和沟后的正常分化需要超吸孔的功能。在没有超级气泡的情况下，沟比正常情况下移动得更快，后部的细胞接合发生得更快。这些表型表明含有超吸二聚体的抑制以及在形态发生沟附近或内部抑制和激活的可能性。一种候选的共抑制因子在眼睛中表达。工作将针对usp，其二聚化伙伴和共同抑制伙伴在控制沟运动和沟后分化中的作用。实验将测试usp的沟前和沟后功能的独立性，并专门解决前抑制机制和配体诱导的形态发生沟内激活的可能性和机制。最可能被usp抑制和激活的核受体伙伴将在该系统中使用体外产生的显性突变来测试其功能。果蝇眼睛发育的调控系统与哺乳动物的肢体、心脏、眼睛和神经系统的调控系统高度相似，这使得这些研究结果极有可能为其他生物的多个过程提供见解。

Nuclear receptor complexes have long been known as ligand-activated transcription factors. Recent cell culture work strongly suggests that nuclear receptor dimers can act negatively as well as positively on a single promoter. Nuclear receptor-mediated repression depends on nuclear receptor co-repressors which bind to ligand free nuclear receptor dimers. These co-repressors are displaced by ligand, removing repression, and allowing activating factors to bind.In order to study the in vivo role of nuclear receptors and their co-repressor partners, experiments will examine the role of RXR-containing dimers in the regulation of cell fate, differentiation and the coordination of development, using the Drosophila eye as an experimentally amenable system. To allow genetic, developmental and molecular approaches to the problem, in the context of otherwise normal development, experiments focus on the role of ultraspiracle (usp), the Drosophila RXR, in control of morphogenetic furrow movement and the earliest stages of cellular differentiation in the eye.The developing Drosophila eye offers an excellent model to study an RXR-mediated activation/repression system. The eye primordium is marked by a visible constriction, the morphogenetic furrow, separating the posterior and anterior regions. The morphogenetic furrow moves from posterior to anterior across the primordium. Cells in the anterior region are undifferentiated and have not committed to any particular fate. In the posterior cell commitment and differentiation occur in a reproducible and stereotypical manner.Normal movement of the morphogenetic furrow and normal differentiation posterior to the furrow require the function of ultraspiracle. In the absence of ultraspiracle, the furrow moves more quickly than normal and cell commitment in the posterior occurs more rapidly. These phenotypes suggest repression by ultraspiracle-containing dimers and the possibility of both relief of repression and activation near or within the morphogenetic furrow. A candidate co-repressor is expressed in the eye.Work will be directed at the role of usp, its dimerization partners and co-repressor partners in the control of furrow movement and post-furrow differentiation. Experiments will test the independence of pre-furrow and post-furrow functions of usp as well as specifically addressing the mechanism of anterior repression and the possibility and mechanism of ligand-induced activation within the morphogenetic furrow. The most likely nuclear receptor partner for repression and activation by usp will be tested for function in this system using in vitro produced dominant mutations.The high degree of similarity between the regulatory systems operating in the Drosophila eye development and in mammalian limb, heart, eye and nervous system makes it extremely likely that the results of these studies will give insight into multiple processes in other organisms.