Dissociating mechanisms that underlie seasonal and developmental programs for the neuroendocrine control of physiology in birds.

Long-term programmed rheostatic changes in physiology are essential for animal fitness. Hypothalamic nuclei and the pituitary gland govern key developmental and seasonal transitions in reproduction. The aim of this study was to identify the molecular substrates that are common, and unique to developmental and seasonal timing. Adult and juvenile quail were collected from reproductively mature and immature states and key molecular targets examined in the mediobasal hypothalamus (MBH) and pituitary gland. qPCR assays established deiodinase type-2 ( DIO2 ) and type-3 ( DIO3 ) expression in adults changed with photoperiod manipulations. However, DIO2 and DIO3 remain constitutively expressed in juveniles. Pituitary gland transcriptome analyses established 340 transcripts were differentially expressed across seasonal photoperiod programs; and 1189 transcripts displayed age-dependent variation in expression. Prolactin ( PRL ) and follicle-stimulating hormone subunit beta ( FSHβ ) are molecular markers of seasonal programs and are significantly upregulated in long photoperiod conditions. Growth hormone expression was significantly upregulated in juvenile quail, regardless of photoperiodic condition. These findings indicate that a level of cell autonomy in the pituitary gland governs seasonal and developmental programs in physiology. Overall, this paper yields novel insights into the molecular mechanisms that govern developmental programs and adult brain plasticity. Significance statement Seasonal physiology is pervasive in the animal kingdom. While much is known regarding how the brain perceives annual changes in daylength (also referred to as photoperiod) and dynamics of the neuroendocrine control of seasonal physiology in adult animals, studies in juveniles are limited. Here, we assess genome-wide and targeted transcriptomic changes in the pituitary gland, a key brain region connecting photoreception with physiological plasticity in adult and juvenile Japanese quail. The analyses identified several novel transcripts that are correlated with photoperiod- and developmental programs in seasonal physiology. The findings demonstrate a level of pituitary gland cell specificity for the regulation of both development and reproductive fitness, that is dependent on both age and experienced photoperiod.