Rhodopsin is the G protein-coupled receptor in rod photoreceptor cells that initiates vision upon photon capture. The light receptor is normally locked in an inactive state in the dark by the covalently bound inverse agonist 11-cis retinal. Mutations can render the receptor active even in the absence of light. This constitutive activity can desensitize rod photoreceptor cells and lead to night blindness. A G90D mutation in rhodopsin causes the receptor to be constitutively active and leads to congenital stationary night blindness, which is generally thought to be devoid of retinal degeneration. The constitutively active species responsible for the night blindness phenotype is unclear. Moreover, the classification as a stationary disease devoid of retinal degeneration is also misleading. A transgenic mouse model for congenital stationary night blindness that expresses the G90D rhodopsin mutant was examined to better understand the origin of constitutive activity and the potential for retinal degeneration. Heterozygous mice for the G90D mutation did not exhibit retinal degeneration whereas homozygous mice exhibited progressive retinal degeneration. Only a modest reversal of retinal degeneration was observed when transducin signaling was eliminated genetically, indicating that some of the retinal degeneration occurred in a transducin-independent manner. Biochemical studies on purified rhodopsin from mice indicated that multiple species can potentially contribute to the constitutive activity causing night blindness.

中文翻译：

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表达组成性活性G90D视紫红质突变体的小鼠的视网膜变性。

视紫红质是杆状感光细胞中的G蛋白偶联受体，可在捕获光子后启动视觉。光受体通常在黑暗中被共价结合的反向激动剂11-顺式视网膜锁定在惰性状态。突变即使在没有光照的情况下也可以使受体具有活性。这种组成性活动可使杆状感光细胞脱敏并导致夜盲症。视紫红质中的G90D突变导致该受体具有组成性活性，并导致先天性固定性夜盲症，通常认为该病没有视网膜变性。负责夜盲表型的组成型活性物质尚不清楚。此外，没有视网膜变性的固定性疾病的分类也具有误导性。检查了表达G90D视紫红质突变体的先天性静止性夜盲症的转基因小鼠模型，以更好地了解组成性活动的起源和视网膜变性的可能性。G90D突变的杂合子小鼠未表现出视网膜变性，而纯合子小鼠则表现出进行性视网膜变性。当基因转导信号被消除时，仅观察到适度的视网膜变性逆转，表明某些视网膜变性以与转导蛋白无关的方式发生。对来自小鼠的纯化视紫红质的生化研究表明，多种物种可能会导致夜盲症的组成活动。