Miyamoto Y, Sancar A
Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA.
Proc Natl Acad Sci U S A. 1998 May 26;95(11):6097-102. doi: 10.1073/pnas.95.11.6097.
In mammals the retina contains photoactive molecules responsible for both vision and circadian photoresponse systems. Opsins, which are located in rods and cones, are the pigments for vision but it is not known whether they play a role in circadian regulation. A subset of retinal ganglion cells with direct projections to the suprachiasmatic nucleus (SCN) are at the origin of the retinohypothalamic tract that transmits the light signal to the master circadian clock in the SCN. However, the ganglion cells are not known to contain rhodopsin or other opsins that may function as photoreceptors. We have found that the two blue-light photoreceptors, cryptochromes 1 and 2 (CRY1 and CRY2), recently discovered in mammals are specifically expressed in the ganglion cell and inner nuclear layers of the mouse retina. In addition, CRY1 is expressed at high level in the SCN and oscillates in this tissue in a circadian manner. These data, in conjunction with the established role of CRY2 in photoperiodism in plants, lead us to propose that mammals have a vitamin A-based photopigment (opsin) for vision and a vitamin B2-based pigment (cryptochrome) for entrainment of the circadian clock.
在哺乳动物中，视网膜含有负责视觉和昼夜节律光反应系统的光活性分子。视蛋白位于视杆细胞和视锥细胞中，是视觉色素，但它们是否在昼夜节律调节中发挥作用尚不清楚。一部分直接投射到视交叉上核（SCN）的视网膜神经节细胞是视网膜下丘脑束的起源，该束将光信号传递到SCN中的主昼夜节律时钟。然而，尚不清楚神经节细胞是否含有可能作为光感受器的视紫红质或其他视蛋白。我们发现，最近在哺乳动物中发现的两种蓝光光感受器，隐花色素1和2（CRY1和CRY2），在小鼠视网膜的神经节细胞层和内核层中特异性表达。此外，CRY1在SCN中高水平表达，并在该组织中以昼夜节律的方式振荡。这些数据，结合CRY2在植物光周期现象中的既定作用，使我们提出，哺乳动物有基于维生素A的视觉光色素（视蛋白）和基于维生素B2的色素（隐花色素）用于昼夜节律时钟的校准。
