The mechanisms that synchronize the biorhythms of the mammalian retina with the light/dark cycle are independent of those synchronizing the rhythms in the central pacemaker, the suprachiasmatic nucleus. The identity of the photoreceptor(s) responsible for the light entrainment of the retina of mammals is still a matter of debate, and recent studies have reported contradictory results in this respect. Here, we suggest that cryptochromes (CRY), in particular CRY 2, are involved in that light entrainment. CRY are highly conserved proteins that are a key component of the cellular circadian clock machinery. In plants and insects, they are responsible for the light entrainment of these biorhythms, mediated by the light response of their flavin cofactor (FAD). In mammals, however, no light-dependent role is currently assumed for CRY in light-exposed tissues, including the retina. It has been reported that FAD influences the function of mammalian CRY 2 and that human CRY 2 responds to light in Drosophila, suggesting that mammalian CRY 2 keeps the ability to respond to light. Here, we hypothesize that CRY 2 plays a role in the light entrainment of retinal biorhythms, at least in diurnal mammals. Indeed, published data shows that the light intensity dependence and the wavelength sensitivity commonly reported for that light entrainment fits the light sensitivity and absorption spectrum of light-responsive CRY. We propose experiments to test our hypothesis and to further explore the still-pending question of the function of CRY 2 in the mammalian retina.

中文翻译：

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视网膜生物节律的光夹带：隐花色素 2 作为哺乳动物的候选光感受器。


哺乳动物视网膜生物节律与光/暗周期同步的机制独立于中央起搏器视交叉上核节律的同步机制。负责哺乳动物视网膜光夹带的光感受器的身份仍然是一个有争议的问题，最近的研究报告了这方面相互矛盾的结果。在这里，我们建议隐花色素 (CRY)，特别是 CRY 2，参与了这种光夹带。 CRY 是高度保守的蛋白质，是细胞生物钟机制的关键组成部分。在植物和昆虫中，它们负责这些生物节律的光夹带，由黄素辅因子 (FAD) 的光反应介导。然而，在哺乳动物中，目前认为 CRY 在暴露于光的组织（包括视网膜）中不具有光依赖性作用。据报道，FAD影响哺乳动物CRY 2的功能，而人类CRY 2在果蝇中对光有反应，表明哺乳动物CRY 2保留了对光反应的能力。在这里，我们假设 CRY 2 在视网膜生物节律的光夹带中发挥作用，至少在昼夜哺乳动物中是这样。事实上，已发表的数据表明，通常报道的光夹带的光强度依赖性和波长敏感性符合光响应 CRY 的光敏感性和吸收光谱。我们提出实验来检验我们的假设并进一步探索 CRY 2 在哺乳动物视网膜中的功能这一仍然悬而未决的问题。