Karpilow J M, Pimentel A C, Shamloula H K, Venkatesh T R
Department of Biology, City College, New York, New York 10031, USA.
J Neurobiol. 1996 Oct;31(2):149-65. doi: 10.1002/(SICI)1097-4695(199610)31:2<149::AID-NEU2>3.0.CO;2-B.
The compound eye of Drosophila is a reiterated pattern of 800 unit eyes known as ommatidia. In each ommatidium there are eight photoreceptor neurons (R1-R8) and an invariant number of accessory cells organized in a precise manner. In the developing eye, specification of cell fates is triggered by sequential inductive events mediated by cell-cell interactions. The R8 photoreceptor neuron is the first cell to differentiate and is thought to play a central role in the recruitment of the remaining photoreceptor cells. Our previous work demonstrated that mutations in the retina aberrant in pattern (rap) locus lead to abnormal pattern formation in the compound eye. Genetic mosaic experiments demonstrated that for normal retinal patterning to occur, rap gene function is required only in the photoreceptor cell R8. In this study we analyzed the R cell composition of developing as well as the adult eyes of rap mutants employing a variety of R cell specific markers. We show that in rap mutants, although some of the R8-specific markers show normal expression patterns, other aspects of the R8 cell differentiation are abnormal. In addition, the cells R1, R6, and R7 fail to differentiate properly in rap mutants. These results suggest that the rap gene encodes an R8-specific function that plays a role in the determination of the photoreceptor cells R1, R6, and R7.
果蝇的复眼是由800个称为小眼的单位眼重复排列而成的。在每个小眼中，有八个光感受器神经元（R1 - R8）以及数量恒定的辅助细胞，它们以精确的方式组织起来。在发育中的眼睛里，细胞命运的特化是由细胞间相互作用介导的一系列诱导事件触发的。R8光感受器神经元是第一个分化的细胞，并且被认为在招募其余光感受器细胞中起核心作用。我们之前的研究表明，视网膜模式异常（rap）基因座的突变会导致复眼中出现异常的模式形成。遗传镶嵌实验表明，为了实现正常的视网膜模式形成，rap基因功能仅在光感受器细胞R8中是必需的。在这项研究中，我们使用多种R细胞特异性标记分析了rap突变体发育中的眼睛以及成虫眼睛的R细胞组成。我们发现，在rap突变体中，尽管一些R8特异性标记显示出正常的表达模式，但R8细胞分化的其他方面是异常的。此外，R1、R6和R7细胞在rap突变体中不能正常分化。这些结果表明，rap基因编码一种R8特异性功能，该功能在光感受器细胞R1、R6和R7的确定中起作用。
