Homothorax controls a binary Rhodopsin switch in Drosophila ocelli.
Homothorax controls a binary Rhodopsin switch in Drosophila ocelli.
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DOI：
10.1371/journal.pgen.1009460
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发表时间：
2021-07
期刊：
影响因子：
4.5
通讯作者：
Sprecher SG
中科院分区：
文献类型：
--
作者：
Mishra AK;Fritsch C;Voutev R;Mann RS;Sprecher SG
环境的视觉感知是由眼睛的专门感光（PR）神经元介导的。每个PR表达光敏视蛋白，其被特定波长的光激活。在大多数昆虫中，视觉系统包括一对主要与运动，颜色或偏振光检测相关的复眼，以及被认为在飞行期间检测地平线和运动的三个单眼。人们普遍认为，昆虫复眼和单眼的进化多样化发生在大约5亿年前的一个祖先视觉器官上。同时，还复制了视蛋白基因，以提供对复眼和单眼的不同PR的不同光谱灵敏度。在果蝇Drosophila melanogaster中，视紫红质1（Rh1）和Rh2是密切相关的视蛋白，其起源于单个祖先基因的复制。然而，在视觉器官中，Rh2在单眼中唯一表达，而Rh1在复眼的外PR中唯一表达。目前尚不清楚Rh1和Rh2在两个视觉器官中的这种差异表达是如何控制的，从而为单眼和复眼提供独特的光谱灵敏度。在这里，我们表明，Homothorax（Hth）在单眼表达，并赋予适当的视紫红质表达。我们发现，Hth控制一个二元视紫红质开关在单眼促进Rh2的表达和抑制Rh1的表达。rh1和rh2的遗传和分子分析支持Hth通过它们的启动子来调节单眼视紫红质的表达。最后，我们还表明，当异位表达在视网膜中，TH是足以诱导Rh2的表达，只有在外部PRs在一个细胞自主的方式。因此，我们提出，在单眼和视网膜外PRs的rhodpsins的多样化发生的祖先基因，这是在同胸的控制下的复制。光的感官知觉是由眼睛的专门感光神经元介导的。每个感光细胞表达独特的色素，称为视蛋白，它们对特定波长的光敏感。单眼和复眼是昆虫的主要感光器官，它们表达不同的视蛋白。据信，视蛋白在进化过程中被复制，以提供单眼和复眼的特异性，这与它们独特的功能相关。我们表明，Homothorax的行为，以控制一个二元视紫红质开关果蝇，促进视紫红质2的表达和抑制视紫红质1的表达单眼。遗传和分子分析表明，同胸通过rhosopsin 1和rhosopsin 2的启动子起作用，并控制它们在单眼中的表达。我们还表明，视紫红质1和视紫红质2的启动子区域中的Hth结合位点在不同的果蝇物种之间是保守的。因此，我们提出，Hth可能是作为一个关键的决定因素，在进化过程中，这是需要提供特异性单眼和复眼通过调节一个二元视紫红质开关单眼。
Visual perception of the environment is mediated by specialized photoreceptor (PR) neurons of the eye. Each PR expresses photosensitive opsins, which are activated by a particular wavelength of light. In most insects, the visual system comprises a pair of compound eyes that are mainly associated with motion, color or polarized light detection, and a triplet of ocelli that are thought to be critical during flight to detect horizon and movements. It is widely believed that the evolutionary diversification of compound eye and ocelli in insects occurred from an ancestral visual organ around 500 million years ago. Concurrently, opsin genes were also duplicated to provide distinct spectral sensitivities to different PRs of compound eye and ocelli. In the fruit fly Drosophila melanogaster, Rhodopsin1 (Rh1) and Rh2 are closely related opsins that originated from the duplication of a single ancestral gene. However, in the visual organs, Rh2 is uniquely expressed in ocelli whereas Rh1 is uniquely expressed in outer PRs of the compound eye. It is currently unknown how this differential expression of Rh1 and Rh2 in the two visual organs is controlled to provide unique spectral sensitivities to ocelli and compound eyes. Here, we show that Homothorax (Hth) is expressed in ocelli and confers proper rhodopsin expression. We find that Hth controls a binary Rhodopsin switch in ocelli to promote Rh2 expression and repress Rh1 expression. Genetic and molecular analysis of rh1 and rh2 supports that Hth acts through their promoters to regulate Rhodopsin expression in the ocelli. Finally, we also show that when ectopically expressed in the retina, hth is sufficient to induce Rh2 expression only at the outer PRs in a cell autonomous manner. We therefore propose that the diversification of rhodpsins in the ocelli and retinal outer PRs occurred by duplication of an ancestral gene, which is under the control of Homothorax. Sensory perception of light is mediated by specialized photoreceptor neurons of the eye. Each photoreceptor expresses unique photopigments called opsins and they are sensitive to particular wavelengths of light. In insects, ocelli and compound eyes are the main photosensory organs and they express different opsins. It is believed that opsins were duplicated during evolution to provide specificity to ocelli and the compound eye and this is corelated with their distinct functions. We show that Homothorax acts to control a binary Rhodopsin switch in the fruit fly Drosophila melanogaster to promote Rhodopsin 2 expression and represses Rhodopsin 1 expression in the ocelli. Genetic and molecular analysis showed that Homothorax acts through the promoters of rhosopsin 1 and rhosopsin 2 and controls their expression in the ocelli. We also show that Hth binding sites in the promoter region of rhodopsin 1 and rhodopsin 2 are conserved between different Drosophila species. We therefore proposed that Hth may have acted as a critical determinant during evolution which was required to provide specificity to the ocelli and compound eye by regulating a binary Rhodopsin switch in the ocelli.
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