Fortini M E, Rubin G M
Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Genes Dev. 1990 Mar;4(3):444-63. doi: 10.1101/gad.4.3.444.
The rhodopsin genes of Drosophila melanogaster are expressed in nonoverlapping subsets of photoreceptor cells within the insect visual system. Two of these genes, Rh3 and Rh4, are known to display complementary expression patterns in the UV-sensitive R7 photoreceptor cell population of the compound eye. In addition, we find that Rh3 is expressed in a small group of paired R7 and R8 photoreceptor cells at the dorsal eye margin that are apparently specialized for the detection of polarized light. In this paper we present a detailed characterization of the cis-acting requirements of both Rh3 and Rh4. Promoter deletion series demonstrate that small regulatory regions (less than 300 bp) of both R7 opsin genes contain DNA sequences sufficient to generate their respective expression patterns. Individual cis-acting elements were further identified by oligonucleotide-directed mutagenesis guided by interspecific sequence comparisons. Our results suggest that the Drosophila rhodopsin genes share a simple bipartite promoter structure, whereby the proximal region constitutes a functionally equivalent promoter "core" and the distal region determines cell-type specificity. The expression patterns of several hybrid rhodopsin promoters, in which all or part of the putative core regions have been replaced with the analogous regions of different rhodopsin promoters, provide additional evidence in support of this model.
黑腹果蝇的视紫红质基因在昆虫视觉系统内的光感受器细胞非重叠亚群中表达。已知其中两个基因Rh3和Rh4在复眼的紫外线敏感R7光感受器细胞群体中呈现互补的表达模式。此外，我们发现Rh3在背侧眼缘的一小群成对的R7和R8光感受器细胞中表达，这些细胞显然专门用于检测偏振光。在本文中，我们详细描述了Rh3和Rh4的顺式作用要求。启动子缺失系列表明，两个R7视蛋白基因的小调控区域（小于300 bp）包含足以产生其各自表达模式的DNA序列。通过种间序列比较指导的寡核苷酸定向诱变进一步鉴定了单个顺式作用元件。我们的结果表明，果蝇视紫红质基因共享一个简单的二分启动子结构，近端区域构成功能上等效的启动子“核心”，远端区域决定细胞类型特异性。几个杂交视紫红质启动子的表达模式，其中全部或部分推定的核心区域已被不同视紫红质启动子的类似区域取代，为该模型提供了额外的支持证据。
