The present study investigated seasonal alterations in the daily rhythms of hypothalamic expression of genes involved in the photoperiodic regulation of annual cycles in birds. We measured the 4-hourly mRNA expression of genes involved in the photoperiodic transduction (OPN5, EYA3, CGA, TSHβ, DIO2, DIO3) and neurosteroid-dependent processes (AR, CYP19, ERα, ERβ) in the hypothalamus of migratory blackheaded buntings photoinduced with photosensitive, photostimulated (early and late stimulated) and photorefractory seasonal states. There were significant differences in daily mRNA profiles between the photoperiodic states. Particularly, increased CGA, TSHβ and DIO2 and decreased DIO3 mRNA levels in the early photostimulated state, compared to the photosensitive state, suggest that thyroid hormones have a role in photostimulation in buntings. Similar differences in the expression of genes coding for the aromatase enzyme (CYP19) and receptors for oestrogen (ERα, ERβ) (but not androgen; AR) indicate that there is seasonal alteration in the neuro-oestrogen-mediated functions. Furthermore, peak expression times of CGA, TSHβ and DIO2 genes at hours 14-15 of the day in the early stimulated state indicated molecular regulation of the daily rhythm of photoinducibility in buntings. Most significantly, however, we found an attenuated daily rhythm in thyroid hormone modulatory genes and a switch of peak expression time from day to night in CYP19 mRNA rhythm in the subsequent late photostimulated state, although testicular maturation still persisted. These alterations in daily rhythms may have signalled the initiation of processes underlying other seasonal phenologies in parallel with the gonadal response, such as a manifestation of the night-time flight in buntings. These results show alterations in daily rhythms underlying the transcriptional regulation of the photoperiod-induced seasonal states in migratory blackheaded buntings.
|Journal||Journal of Neuroendocrinology|
|State||Published - May 2017|
Bibliographical noteFunding Information:
Funding information Funds for the present study were provided by the Department of Biotechnology, New Delhi, through a research grant (BT/PR4984/MED/30/752/2012) to VK. IM received a Senior Research Fellowship from the Council of Scientific and Industrial Research, New Delhi. The help rendered by Dr Amit Kumar Trivedi in sampling and by Professor Sangeeta Rani during the experimentation is acknowledged. The experimental facility used for experiments at the University of Lucknow, India, was built with the support from the Science and Engineering Research Board, New Delhi, under IRHPA and regular grants to VK.
© 2017 British Society for Neuroendocrinology
- gene expression
- thyroid hormone
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Endocrine and Autonomic Systems
- Cellular and Molecular Neuroscience