Figure 4.

(Color online) Universality and diversity in the photoperiodic signal transduction pathways in vertebrates. (a) In mammals, light information is detected via the eyes and transmitted through the suprachiasmatic nucleus (SCN) to the pineal gland. The profile of melatonin secretion from the pineal gland encodes photoperiodic information and regulates the thyroid-stimulating hormone (TSH) in the pars tuberalis (PT) of the pituitary gland. (b) In birds, light information is directly received by deep brain photoreceptors and is then transmitted to PT to trigger TSH secretion. (c) In fish, all of the key elements required for seasonal reproduction (from photoreceptors to neuroendocrine output) are integrated within the coronet cells located in saccus vasculosus (SV). Figure reproduced from Nakane and Yoshimura (2014)¹⁰⁶⁾ with permission under the terms of the Creative Commons Attribution License (CC BY) © 2014 Nakane and Yoshimura. Abbreviations: 3V, third ventricle; DIO2, type 2 deiodinase; ECs, ependymal cells.