Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.
Department of Biology, University of Victoria, Victoria, British Columbia, Canada.
J Comp Neurol. 2021 Aug 1;529(11):3013-3031. doi: 10.1002/cne.25144. Epub 2021 Apr 6.
Visual opsins are proteins expressed by retinal photoreceptors that capture light to begin the process of phototransduction. In vertebrates, the two types of photoreceptors (rods and cones) express one or multiple opsins and are distributed in variable patterns across the retina. Some cones form opsin retinal gradients, as in the mouse, whereas others form more demarcated opsin domains, as in the lattice-like mosaic retinas of teleost fishes. Reduced rod opsin (rh1) expression in mouse, zebrafish, and African clawed frog results in lack of photoreceptor outer segments (i.e., the cilium that houses the opsins) and, in the case of the mouse, to retinal degeneration. The effects of diminished cone opsin expression have only been studied in the mouse where knockout of the short-wavelength sensitive 1 (sws1) opsin leads to ventral retinal cones lacking outer segments, but no retinal degeneration. Here we show that, following CRISPR/Cas9 injections that targeted knockout of the sws1 opsin in rainbow trout, fish with diminished sws1 opsin expression exhibited a variety of developmental defects including head and eye malformations, underdeveloped outer retina, mislocalized opsin expression, cone degeneration, and mosaic irregularity. All photoreceptor types were affected even though sws1 is only expressed in the single cones of wild fish. Our results reveal unprecedented developmental defects associated with diminished cone opsin expression and suggest that visual opsin genes are involved in regulatory processes that precede photoreceptor differentiation.
视蛋白是视网膜光感受器表达的蛋白质，它捕获光以开始光转导过程。在脊椎动物中，两种类型的光感受器（杆状细胞和锥状细胞）表达一种或多种视蛋白，并以不同的模式分布在视网膜上。一些锥状细胞形成视蛋白视网膜梯度，如在小鼠中，而另一些则形成更明显的视蛋白域，如在硬骨鱼的晶格状镶嵌视网膜中。在小鼠、斑马鱼和非洲爪蟾中，减少视杆细胞视蛋白（rh1）的表达导致光感受器外节（即包含视蛋白的纤毛）缺失，而在小鼠中则导致视网膜变性。只有在小鼠中研究了减少视锥细胞视蛋白表达的影响，在那里敲除短波长敏感 1（sws1）视蛋白导致腹侧视网膜锥体细胞缺乏外节，但没有视网膜变性。在这里，我们展示了，在虹鳟鱼中针对 sws1 视蛋白进行 CRISPR/Cas9 注射以靶向敲除后，sws1 视蛋白表达减少的鱼类表现出多种发育缺陷，包括头部和眼睛畸形、外视网膜发育不良、视蛋白表达错位、锥状细胞变性和镶嵌不规则。尽管 sws1 仅在野生鱼类的单个锥状细胞中表达，但所有感光细胞类型都受到影响。我们的结果揭示了与减少视锥细胞视蛋白表达相关的前所未有的发育缺陷，并表明视觉视蛋白基因参与了发生在光感受器分化之前的调控过程。
