Direct photoreception by pituitary endocrine cells regulates hormone release and pigmentation

The recent discovery of nonvisual photoreceptors in various organs has raised expectations for uncovering their roles and underlying mechanisms. In this work, we identified a previously unrecognized hormone-releasing mechanism in the pituitary of the Japanese rice fish (medaka) induced by light. Ca ²⁺ imaging analysis revealed that melanotrophs, a type of pituitary endocrine cell that secretes melanocyte-stimulating hormone, robustly increase the concentration of intracellular Ca ²⁺ during short-wavelength light exposure. Moreover, we identified Opn5m as the key molecule that drives this response. Knocking out opn5m attenuated melanogenesis by reducing tyrosinase expression in the skin. Our findings suggest a mechanism in which direct reception of short-wavelength light by pituitary melanotrophs triggers a pathway that might contribute to protection from ultraviolet radiation in medaka.