VA Opsin-Based Photoreceptors in the Hypothalamus of Birds

• Published in: Current biology 2009-08, Vol.19 (16), p.1396-1402
• Main Authors: 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.
• Format: Article
• Language: English
• Subjects: Agnatha; Animals; Aves; Base Sequence; Cells, Cultured - radiation effects; Chickens - genetics; Chickens - physiology; DNA, Complementary - genetics; EVO_ECOL; Fishes - genetics; Fishes - physiology; Gonadotropin-Releasing Hormone - secretion; Hypothalamo-Hypophyseal System - physiology; Hypothalamus - cytology; Hypothalamus - physiology; Median Eminence - cytology; Median Eminence - secretion; Molecular Sequence Data; MOLNEURO; Neurons - chemistry; Neurons - physiology; Opsins - genetics; Opsins - isolation & purification; Opsins - physiology; Opsins - radiation effects; Photic Stimulation; Photoperiod; Photoreceptor Cells, Vertebrate - chemistry; Photoreceptor Cells, Vertebrate - physiology; Phylogeny; Pituitary Gland, Anterior - secretion; Protein Isoforms - physiology; Recombinant Fusion Proteins - physiology; Recombinant Fusion Proteins - radiation effects; Species Specificity; Teleostei; Thyrotropin - secretion; Triiodothyronine - biosynthesis; Triiodothyronine - physiology
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2009.06.066

Studies in the 1930s demonstrated that birds possess photoreceptors that are located within the hypothalamus and regulate photoperiodic responses to day length [1, 2]. Most recently, photoperiod has been shown to alter the activity of the pars tuberalis to release thyrotrophin, which ultimately drives a reproductive response [3, 4]. 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 [5], but further identification based on rod- or cone-opsin probes failed, suggesting the utilization of a novel opsin [6]. The vertebrate ancient ( VA) opsin photopigments were isolated in 1997 [7, 8] 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.