Mazzoni Esteban O, Celik Arzu, Wernet Mathias F, Vasiliauskas Daniel, Johnston Robert J, Cook Tiffany A, Pichaud Franck, Desplan Claude
Center for Developmental Genetics, Department of Biology, New York University, New York, New York, United States of America.
PLoS Biol. 2008 Apr 22;6(4):e97. doi: 10.1371/journal.pbio.0060097.
The Drosophila eye is a mosaic that results from the stochastic distribution of two ommatidial subtypes. Pale and yellow ommatidia can be distinguished by the expression of distinct rhodopsins and other pigments in their inner photoreceptors (R7 and R8), which are implicated in color vision. The pale subtype contains ultraviolet (UV)-absorbing Rh3 in R7 and blue-absorbing Rh5 in R8. The yellow subtype contains UV-absorbing Rh4 in R7 and green-absorbing Rh6 in R8. The exclusive expression of one rhodopsin per photoreceptor is a widespread phenomenon, although exceptions exist. The mechanisms leading to the exclusive expression or to co-expression of sensory receptors are currently not known. We describe a new class of ommatidia that co-express rh3 and rh4 in R7, but maintain normal exclusion between rh5 and rh6 in R8. These ommatidia, which are localized in the dorsal eye, result from the expansion of rh3 into the yellow-R7 subtype. Genes from the Iroquois Complex (Iro-C) are necessary and sufficient to induce co-expression in yR7. Iro-C genes allow photoreceptors to break the "one receptor-one neuron" rule, leading to a novel subtype of broad-spectrum UV- and green-sensitive ommatidia.
果蝇的眼睛是一种镶嵌体，由两种小眼亚型的随机分布形成。浅色和黄色小眼可以通过其内部光感受器（R7和R8）中不同视紫红质和其他色素的表达来区分，这些色素与颜色视觉有关。浅色亚型在R7中含有吸收紫外线（UV）的Rh3，在R8中含有吸收蓝光的Rh5。黄色亚型在R7中含有吸收紫外线的Rh4，在R8中含有吸收绿光的Rh6。每个光感受器仅表达一种视紫红质是一种普遍现象，尽管也有例外情况。目前尚不清楚导致感觉受体单独表达或共表达的机制。我们描述了一类新的小眼，它们在R7中共表达rh3和rh4，但在R8中保持rh5和rh6之间的正常排斥。这些位于背侧眼的小眼是由于rh3扩展到黄色R7亚型中而产生的。来自易洛魁复合体（Iro-C）的基因对于在黄色R7中诱导共表达是必要且充分的。Iro-C基因使光感受器能够打破“一个受体-一个神经元”规则，从而产生一种新型的广谱紫外线和绿色敏感小眼亚型。
