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

果蝇复眼发育中的图案形成主要是诱导性细胞间信号事件的结果。大约20年前，在较大的苍蝇（蝇属，丽蝇属）中，已经认识到分化复眼中一种非常有趣但知之甚少的模式：两种内感光细胞亚型R7和R8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节表达。一个细胞对表达“奇数”视紫红质组合Rh 3和Rh 5，另一个细胞对表达“偶数”视紫红质对Rh 4和Rh 6。R8和R8细胞视紫红质的这种协调表达被认为是由相邻的表达Rh 3的R7细胞（“奇数”对）诱导R8细胞中Rh 5表达的结果，而不是“偶数”对的R8细胞中表达Rh 6的默认途径。无论是假定的诱导信号通路的R7到R8细胞的组件，也不知道的发展机制，程序R8细胞向Rh 6表达默认状态。我们建议分离果蝇突变体，显示缺陷的R7/R8细胞模式作为一种手段，以确定基因和基因产物，构成这种新的细胞-细胞信号通路，并控制果蝇复眼中的R7和R8细胞的终末分化。该项目在感光细胞分化领域具有特殊的相关性，并有可能深入了解其他生物体和器官系统中模式形成的机制。

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.