Opsin/vitamin A based photopigments in extraretinal photoreceptors
Non-mammalian vertebrates possess a diverse complement of photoreceptors including the pineal organ, deep encephalic photoreceptors, and dermal/peripheral tissue photoreceptors. Although these photoreceptors were first recognised in the early part of the 19th century, the basis for their photosensitivity remained (and to a degree still remains) poorly understood. My work provided overwhelming evidence that these diverse photoreceptors use broadly conserved mechanisms based upon opsin/vitamin A photopigments. Two of my early Nature papers, summarise these conceptual breakthroughs:
- The photosensitive dermal pigment cells of certain teleost fish utilize an opsin-based photopigment system (13). This was shown by generating antibodies against visual pigment opsins, and localising opsin protein in the photosensitive membranes of the dermal iridophores. In 2003 we isolated a new opsin gene family (tmt-opsin) from fish that probably encodes the specific opsin for this peripheral tissue photosensitivity (14). This work is ongoing;
- A study published in 1985, addressed a long-standing question in seasonal physiology. In the 1930’s birds had been shown to use a photoreceptor located deep within the brain to detect daylength changes and regulate seasonal physiology, but nothing was known of how this photoreceptor might function. By using action spectroscopy we established that these encephalic receptors utilize an opsin/vitamin A based photopigment system (2). We were also able to show how the detection of these daylength changes are translated into neuroendocrine changes of the reproductive axis (3).