title: Functional characterisation of the chromatically antagonistic photosensitive mechanism of erythrophores in the tilapia Oreochromis niloticus.
abstract: Non-visual photoreceptors with diverse photopigments allow organisms to adapt to changing light conditions. Whereas visual photoreceptors are involved in image formation, non-visual photoreceptors mainly undertake various non-image-forming tasks. They form specialised photosensory systems that measure the quality and quantity of light and enable appropriate behavioural and physiological responses. Chromatophores are dermal non-visual photoreceptors directly exposed to light and they not only receive ambient photic input but also respond to it. These specialised photosensitive pigment cells enable animals to adjust body coloration to fit environments, and play an important role in mate choice, camouflage and ultraviolet (UV) protection. However, the signalling pathway underlying chromatophore photoresponses and the physiological importance of chromatophore colour change remain under-investigated. Here, we characterised the intrinsic photosensitive system of red chromatophores (erythrophores) in tilapia. Like some non-visual photoreceptors, tilapia erythrophores showed wavelength-dependent photoresponses in two spectral regions: aggregations of inner pigment granules under UV and short-wavelengths and dispersions under middle- and long-wavelengths. The action spectra curve suggested that two primary photopigments exert opposite effects on these light-driven processes: SWS1 (short-wavelength sensitive 1) for aggregations and RH2b (rhodopsin-like) for dispersions. Both western blot and immunohistochemistry showed SWS1 expression in integumentary tissues and erythrophores. The membrane potential of erythrophores depolarised under UV illumination, suggesting that changes in membrane potential are required for photoresponses. These results suggest that SWS1 and RH2b play key roles in mediating intrinsic erythrophore photoresponses in different spectral ranges and this chromatically dependent antagonistic photosensitive mechanism may provide an advantage to detect subtle environmental photic change.
authors.affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6 shyhchi.chen@mail.huji.ac.il.
authors.forename: Shyh-Chi
authors.initials: SC
authors.lastname: Chen
authors.affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: Chengfeng
authors.initials: C
authors.lastname: Xiao
authors.affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6 Department of Psychology, Queen's University, Kingston, Ontario, Canada K7L 3N6 Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: Nikolaus F
authors.initials: NF
authors.lastname: Troje
authors.affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6 Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: R Meldrum
authors.initials: RM
authors.lastname: Robertson
authors.affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6 Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: Craig W
authors.initials: CW
authors.lastname: Hawryshyn
mesh_terms: D000818:Animals; D002856:Chromatophores / Q000502:physiology / Q000528:radiation effects*; D023681:Cichlids / Q000502:physiology*; D008027:Light; D008297:Male; D055355:Opsins / Q000502:physiology / Q000528:radiation effects; D010786:Photoreceptor Cells / Q000166:cytology / Q000528:radiation effects*; D010858:Pigmentation; D012168:Retinal Pigments / Q000737:chemistry / Q000502:physiology / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D055355:Opsins; D012168:Retinal Pigments
keywords: Chromatophores; Opsins; Photoreceptors; Pigment cells; Visual pigments