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 reproduc tively mature and immature states, and key molecular targets were examined in the mediobasal hypo thalamus (MBH) and pituitary gland. qRT-PCR 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 that 340 tran scripts were differentially expressed across seasonal photoperiod programs and 1,189 transcripts dis played 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 pho toperiod 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 pitu itary 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. Five-week-old male Japanese quail (Coturnix japonica) were acclimated to a long photoperiod for 2 weeks. Then birds were placed on nonstimulatory photoperiods to induce gonadal involution and collected in short days (8L) after 8 weeks. A subset of short-day birds (n=5) was humanely killed using cervical dislocation followed by decapitation. Another group (n=5) was placed on stimulatory photoperiods to induce gonadal growth and collected in a long photoperiod after 8 weeks. Newly hatched chicks were acclimated to a long photoperiod for 5 days. Birds were divided into 2 groups and assigned to either a long (16L, n=4) or short (8L, n=5) photoperiod for 5 days. On posthatch day 10, chicks were killed by cervical dislocation followed by decapitation. For all birds (adults and chicks), brain and pituitary tissues were frozen on dry ice and stored at -70 Celsiius. During collections, the pituitary stalk was severed, leaving the pars tuberalis attached to the mediobasal hypothalamus. Pituitary tissue including the pars distalis was dissected from the sella turcica and retained for both qRT-PCR analyses and Oxford Nanopore RNA-sequencing.