Inductive signaling pathways determining paired rhodopsin expression in R7/R8 cells of the Drosophila compound eye

果蝇复眼发育中的模式形成主要是诱导细胞-细胞信号事件的结果。近20年前，在大型果蝇（Musca, Calliphora）中发现了分化复眼的一个非常有趣但鲜为人知的模式：内部感光细胞R7和R8的两种亚型以配对的方式随机分布在复眼中。我们和其他人最近的工作表明，这些匹配对对应于R7和R8细胞的视紫红质的精确调控表达。一个细胞对表达“奇数”视紫质组合Rh3和Rh5，另一个细胞对表达“偶数”视紫质组合Rh4和Rh6。R8和R8细胞紫红质的协调表达被认为是R8细胞中邻近表达rh3的R7细胞（“奇数”对）诱导Rh5表达的结果，而不是R8细胞中表达rh6的默认途径（“偶数”对）。从R7到R8细胞的诱导信号通路的组成部分，以及将R8细胞编程为表达rh6默认状态的发育机制都不清楚。我们提出分离R7/R8细胞模式缺陷的果蝇突变体，作为鉴定构成这一新的细胞-细胞信号通路并控制果蝇复眼R7和R8细胞终末分化的基因和基因产物的手段。该项目在光感受器细胞分化领域具有特殊的相关性，并可能为其他生物体和器官系统的模式形成机制提供见解。

Pattern formation in the developing compound eye of Drosophila is primarily a result of inductive cell-cell signaling events. A highly interesting but poorly understood pattern in the differentiated compound eye has been recognized almost two decades ago in larger flies (Musca, Calliphora): Two subtypes of the inner photoreceptor cells R7 and R8 are organized in matched pairs randomly distributed across the compound eye. Our and others recent work revealed that these matched pairs correspond to a precisely regulated expression of the rhodopsins of R7 and R8 cells. One cell pair expresses the "odd" rhodopsin combination Rh3 and Rh5, the other cell pair expresses the "even" numbered rhodopsin pair Rh4 and Rh6. This coordinated expression of R8 and R8 cell rhodopsins is proposed to be the result of an induction of Rh5 expression in the R8 cell by the adjacent Rh3-expressing R7 cell ("odd" pair), versus an Rh6-expressing default pathway in the R8 cell of the "even" pair. Neither the components of the postulated inductive signaling pathway from R7 to R8 cells nor the developmental mechanisms which programm the R8 cell towards the Rh6-expressing default state are know. We propose to isolate Drosophila mutants which show defects in the R7/R8 cell pattern as a means to identify the genes and gene products which constitute this novel cell-cell signaling pathway and control the terminal differentiation of R7 and R8 cells in the Drosophila compound eye. The project has special relevance within the field of photoreceptor cell differentiation and is likely to provide insight into the mechanisms of pattern formation in other organisms and organ systems.