Chou W H, Huber A, Bentrop J, Schulz S, Schwab K, Chadwell L V, Paulsen R, Britt S G
Institute of Biotechnology and Department of Molecular Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78245-3207, USA.
Development. 1999 Feb;126(4):607-16. doi: 10.1242/dev.126.4.607.
Opsin gene expression in the R7 and R8 photoreceptor cells of the Drosophila compound eye is highly coordinated. We have found that the R8 cell specific Rh5 and Rh6 opsins are expressed in non-overlapping sets of R8 cells, in a precise pairwise fashion with Rh3 and Rh4 in the R7 cells of individual ommatidia. Removal of the R7 cells in sevenless, boss or sina mutants, disrupts Rh5 expression and dramatically increases the number of Rh6-expressing R8 cells. This suggests that the expression of Rh5 may be induced by an Rh3-expressing R7 cell, whereas Rh6 expression is most likely a default state of the R8 cell. We found that the paired expression of opsin genes in the R7 and R8 cells occurs in a sevenless and boss independent manner. Furthermore, we found that the generation of both Rh3- and Rh4-expressing R7 cells can occur in the absence of an R8 cell. These results suggest that the specification of opsin expression in the R7 cells may occur autonomously, whereas the R7 photoreceptor cell may be responsible for regulating a binary developmental switch between induced and default cell-fates in the R8 cell.
果蝇复眼中R7和R8光感受器细胞中的视蛋白基因表达高度协调。我们发现，R8细胞特异性的Rh5和Rh6视蛋白在不重叠的R8细胞组中表达，与单个小眼的R7细胞中的Rh3和Rh4以精确的成对方式表达。在无七（sevenless）、boss或sina突变体中去除R7细胞，会破坏Rh5的表达，并显著增加表达Rh6的R8细胞数量。这表明Rh5的表达可能由表达Rh3的R7细胞诱导，而Rh6的表达很可能是R8细胞的默认状态。我们发现，R7和R8细胞中视蛋白基因的成对表达以一种不依赖无七和boss的方式发生。此外，我们发现，在没有R8细胞的情况下，表达Rh3和Rh4的R7细胞都可以产生。这些结果表明，R7细胞中视蛋白表达的特化可能是自主发生的，而R7光感受器细胞可能负责调节R8细胞中诱导和默认细胞命运之间的二元发育开关。
