Abstract
Pineal and related organs are major extraocular photoreceptors in non-mammalian vertebrates. The pineal organ contains several types of photoreceptor cells, which contribute to regulating light-dependent melatonin secretion and the neural light response, including irradiance detection and wavelength discrimination. Visual opsins and pineal-specific opsins have been identified from the pineal and related organs in a wide variety of non-mammalian vertebrates. Pinopsin and parapinopsin are key opsins for understanding melatonin secretion in the chicken pineal organ and wavelength discrimination in the lamprey pineal organ, respectively. Interestingly, parapinopsin has the molecular characteristics of both vertebrate and invertebrate opsin-based pigments, making it an important photopigment for understanding the molecular evolution of vertebrate visual opsins. In this chapter, we discuss the opsin-based pigments functioning in the pineal and related organs with a focus on parapinopsin.
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