FSHβ links photoperiodic signalling to seasonal reproduction in Japanese quail

Abstract

Endogenous programs in avian reproductive seasonal life history transitions have been known for over 30 years. Attempts to identify the neural and molecular substrates of photoperiodic time measurement have, to date, focussed on blunt changes in light exposure during a restricted period of photoinducibility. Here we report mediobasal hypothalamus (MBH) and pituitary gland specific transcript expression cascades associated with photoperiod-induced seasonal life history transitions. We identified multiple waves of transcript expression that were not synchronized across brain regions. Follicle-stimulating hormone-β (FSHβ) expression increased during the simulated vernal equinox, prior to photoinduced increases in prolactin, thyrotropin-stimulating hormone-β and testicular growth. Analyses showed sustained elevated levels of daily FSHβ expression in the pituitary under conditions of the vernal, compared to autumnal equinox, short (<12L) and long (>12L) photoperiods. FSHβ expression increased in Quail held in non-stimulatory photoperiod, indicative of an endogenous programmed change in transcription. These data identify that FSHβ provides an endogenous program for the photoperiod-dependent external coincidence timing for seasonal transitions in reproduction. FSHβ may prime the pituitary for subsequent stimulation by triiodothyronine-mediated changes in tanycytes during the photoinducible phase. Overall, the data indicate a multi-cellular, multi-neural interval timing mechanism resides in the brain to control seasonal life-history transitions in birds.