Transcriptomic seasonality in the hippocampus and amygdala/nucleus taeniae of quail and hamsters

Both birds and mammals use seasonal photoreception to precisely time life history transitions. The neuroendocrine control of reproductive physiology is underpinned by deep brain photoreception in birds, whereas in mammals the nocturnal melatonin signalling via retinal photoreception is essential. Light stimuli is known to impact the hippocampus and amygdala (or nucleus taeniae in birds), brain regions important for perception of social cues and emotional processing. The hippocampus in particular shows seasonal plasticity in size and dendritic complexity. The molecular basis of seasonal plasticity in these limbic brain regions is not well characterised. This study developed the transcriptomic architecture of the hippocampus and amygdala/nucleus taeniae in Japanese quail and Siberian hamsters using Oxford Nanopore RNA-sequencing to investigate photoperiodic and taxonomic differences in the seasonal plasticity of these brain regions. Physiological variation across photoperiod was apparent in body mass, testes mass, and pelage. A large number of transcripts of potential interest were identified, including TTR and MGRN1, providing solid links to the reproductive response to differential photoperiod and indicating that both brain regions respond robustly to photoperiodic manipulation. Both the hippocampus and amygdala/nucleus taeniae demonstrated primarily long-day downregulation of transcript expression. These results provide key insight into the transcriptomic architecture of two highly seasonal brain regions, suggesting a high level of unique transcript specificity across taxa. Birds and mammals respond similarly to seasonal photoperiodic cues via very different transcriptomic routes.