Korenbrot J I, Fernald R D
Department of Physiology, School of Medicine, University of California, San Francisco 94143.
Nature. 1989 Feb 2;337(6206):454-7. doi: 10.1038/337454a0.
Disk membranes in the outer segment of rod photoreceptors are continuously renewed, being assembled at the outer segment base, displaced outward by new disks and eventually shed at the tip. In lower vertebrates, disk assembly occurs with a diurnal rhythm with 2-4% of the outer segment length produced daily. We have discovered that in toad and fish retinas the level of mRNA for opsin, the most abundant protein in rod disks, fluctuates with a daily rhythm and is regulated both by light and by a circadian oscillator. The mRNA level rises before light onset, remains high during the light phase of a diurnal cycle and decreases four to tenfold during the dark phase. In constant darkness, mRNA elevation occurs during subjective daytime. At night, rod opsin mRNA can be elevated by exposure to light.
视杆光感受器外段的盘状膜不断更新，在外段基部组装，被新的盘状膜向外推移，最终在顶端脱落。在低等脊椎动物中，盘状膜的组装具有昼夜节律，每天产生的外段长度为2-4%。我们发现，在蟾蜍和鱼类视网膜中，视蛋白（视杆盘状膜中最丰富的蛋白质）的mRNA水平随昼夜节律波动，并且受光照和生物钟振荡器的调节。mRNA水平在光照开始前升高，在昼夜周期的光照阶段保持较高水平，在黑暗阶段下降4至10倍。在持续黑暗中，mRNA升高发生在主观白天。在夜间，暴露于光照下可使视杆视蛋白mRNA升高。
