Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, United Kingdom.
Invest Ophthalmol Vis Sci. 2013 Jan 28;54(1):821-9. doi: 10.1167/iovs.12-10375.
Gap junctional coupling between rod and cone photoreceptor cells is regulated by light and the circadian clock, and contributes to retinal light adaptation. Phosphorylation of connexin 36 (Cx36) has been proposed as the mechanism involved. We investigated whether retinal Cx36 is also regulated at the level of transcript and protein expression.
At specific time points in a diurnal or circadian cycle, Cx36 protein was assessed by Western blotting and immunohistochemistry, and Cx36 transcript by quantitative real time PCR in a melatonin-deficient (C57BL6/FVB) and two melatonin-proficient (C3H(+/+) and C3H(rd/rd)) mouse strains.
In C57BL6/FVB mice during a diurnal cycle, Cx36 protein expression was rhythmic, peaking at approximately zeitgeber time (ZT) 20. However, this rhythm was not maintained in the circadian cycle. In C3H(+/+) mice levels of Cx36 protein were higher at night and subjective night relative to day and subjective day, respectively. These patterns of Cx36 expression were localized primarily to the outer plexiform layer in both strains. Cx36 transcript expression was higher at night and subjective night relative to day and subjective day in C57BL6/FVB and C3H(+/+) mice. Rhythmic expression of Cx36 transcript was lost in retinally degenerate C3H(rd/rd) mice.
The results suggested the circadian control of Cx36 protein expression is dependent on melatonin, whereas the circadian regulation of Cx36 transcript expression may be controlled directly by the circadian clock. In addition to post-translational modification, regulation of Cx36 transcript and protein expression may be important during retinal light adaptation.
杆状和锥状光感受器细胞之间的缝隙连接偶联受光和生物钟调节，有助于视网膜光适应。磷酸化连接蛋白 36（Cx36）被认为是相关机制。我们研究了视网膜 Cx36 是否也受转录和蛋白表达水平的调节。
在昼夜或生物钟周期的特定时间点，通过 Western 印迹和免疫组织化学评估 Cx36 蛋白，通过实时定量 PCR 评估 Cx36 转录，研究对象为褪黑素缺乏（C57BL6/FVB）和两种褪黑素丰富（C3H（+/+）和 C3H（rd/rd））的小鼠品系。
在 C57BL6/FVB 小鼠的昼夜周期中，Cx36 蛋白表达呈节律性，约在 Zeitgeber 时间（ZT）20 时达到峰值。然而，这种节律在生物钟周期中无法维持。在 C3H（+/+）小鼠中，Cx36 蛋白水平在夜间和主观夜间相对白天和主观白天更高。这些 Cx36 表达模式主要定位于两种品系的外丛状层。在 C57BL6/FVB 和 C3H（+/+）小鼠中，Cx36 转录表达在夜间和主观夜间相对白天和主观白天更高。在视网膜变性的 C3H（rd/rd）小鼠中，Cx36 转录的节律性表达丧失。
结果表明，Cx36 蛋白表达的昼夜控制依赖于褪黑素，而 Cx36 转录的昼夜调节可能直接受生物钟控制。除了翻译后修饰外，Cx36 转录和蛋白表达的调节在视网膜光适应过程中可能很重要。
