Direct photoreception of a pituitary endocrine cell, melanotroph, induces a hormone release

In addition to canonical photoreception by the eye, many other organs express non-visual photoreceptors although their biological significance is mostly unknown. Here, we discovered a novel phenomenon in which the pituitary of medaka directly receives light, which induces hormone release. Ca2+ imaging analysis revealed that a melanotroph, a pituitary endocrine cell secreting melanocyte-stimulating hormone (MSH), robustly increases [Ca2+]i during short-wavelength light irradiation. Moreover, we identified Opn5m as the key molecule of this mechanism. The significance of this phenomenon was suggested to be involved in UV protection because knockout of opn5m significantly reduced the expression of tyrosinase, the rate-limiting enzyme for melanogenesis, in the skin. These results suggest a novel mechanism in which direct reception of short-wavelength light by pituitary endocrine cells triggers the pathway to enhance UV protection.