FSHβ links photoperiodic signaling 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.

Dissociating Mechanisms That Underlie Seasonal and Developmental Programs for the Neuroendocrine Control of Physiology in Birds

“…The data indicate somatotrophs as a cellular basis of developmental programs, lactotrophs as a marker of photoperiod programs, and gonadotrophs as a mix of both programs (Extended Data Fig. 3-2 ); this conclusion builds on recently published work indicating a pituitary cell autonomy, separate from changes driven by the MBH, in seasonal FSHß expression ( Majumdar et al 2023 ). Our approach to conducting Oxford Nanopore RNA sequencing and qRT-PCR analyses to investigate the photoperiodic and developmental responses in quail provides a robust approach to provide a comprehensive and confirmatory strategy.…”

“…Then 2 mm lateral cuts and a 2 mm dorsal cut were conducted to isolate the MBH. This dissection protocol reliably isolates the MBH in Japanese quail ( Majumdar et al, 2023 ). Brains were then returned to −70°C.…”