Halford Stephanie, Pires Susana S, Turton Michael, Zheng Lei, González-Menéndez Irene, Davies Wayne L, Peirson Stuart N, García-Fernández José M, Hankins Mark W, Foster Russell G
Circadian and Visual Neuroscience, Nuffield Laboratory of Ophthalmology, University of Oxford, Headley Way, Oxford OX3 9DU, UK.
Curr Biol. 2009 Aug 25;19(16):1396-402. doi: 10.1016/j.cub.2009.06.066. Epub 2009 Aug 6.
Studies in the 1930s demonstrated that birds possess photoreceptors that are located within the hypothalamus and regulate photoperiodic responses to day length. Most recently, photoperiod has been shown to alter the activity of the pars tuberalis to release thyrotrophin, which ultimately drives a reproductive response. Despite these significant findings, the cellular and molecular identity of the hypothalamic photoreceptors has remained a mystery. Action spectra implicated an opsin-based photopigment system, but further identification based on rod- or cone-opsin probes failed, suggesting the utilization of a novel opsin. The vertebrate ancient (VA) opsin photopigments were isolated in 1997 but were thought to have a restricted taxonomic distribution, confined to the agnatha and teleost fish. Here, we report the isolation of VA opsin from chicken and show that the two isoforms spliced from this gene (cVAL and cVA) are capable of forming functional photopigments. Further, we show that VA opsin is expressed within a population of hypothalamic neurons with extensive projections to the median eminence. These results provide the most complete cellular and molecular description of a deep brain photoreceptor in any vertebrate and strongly implicate VA opsin in mediating the avian photoperiodic response.
20世纪30年代的研究表明，鸟类拥有位于下丘脑内的光感受器，可调节对日照长度的光周期反应。最近，已证明光周期会改变结节部释放促甲状腺激素的活性，这最终驱动生殖反应。尽管有这些重大发现，但下丘脑光感受器的细胞和分子特性仍是个谜。作用光谱表明存在基于视蛋白的光色素系统，但基于视杆或视锥视蛋白探针的进一步鉴定失败了，这表明使用了一种新型视蛋白。脊椎动物古老（VA）视蛋白光色素于1997年被分离出来，但被认为分类分布有限，仅限于无颌类和硬骨鱼。在此，我们报告从鸡中分离出VA视蛋白，并表明从该基因剪接出的两种异构体（cVAL和cVA）能够形成功能性光色素。此外，我们表明VA视蛋白在下丘脑神经元群体中表达，这些神经元向正中隆起有广泛投射。这些结果提供了对任何脊椎动物深部脑光感受器最完整的细胞和分子描述，并有力地表明VA视蛋白在介导鸟类光周期反应中起作用。
