Photoperiodic regulation of ovarian steroidogenesis in a tropical rodent, Funambulus pennanti: role of melatonin and MT1

ABSTRACT

To elucidate the role of photoperiodically modulated endogenous melatonin and its receptor MT1 in the ovary of a diurnal rodent, adult Indian palm squirrel Funambulus pennanti were exposed to Short Day (SD; 16L:8D) and Long Day (LD; 16L:8D) and compared with natural day controls (NDL; 12L:12D). Plasma 17-β estradiol level was significantly low in SD group while expression of StAR, P₄₅₀SCC, 17-β HSD, and aromatase showed significant down-regulation in the ovary of squirrels maintained under SD when compared to LD and NDL groups suggesting an overall decrease in steroidogenesis. Expression of ERα in the ovary was significantly lower in SD than both LD and NDL groups, having a positive correlation with plasma estradiol level. Circulatory melatonin level was significantly high in SD-exposed squirrels, while expression of MT1R decreased in the ovary when compared to LD and NDL groups, showing a negative correlation with plasma melatonin levels. Expression of cell proliferation marker Proliferating Cell Nuclear Antigen (PCNA) was positively correlated to MT1R expression in the ovary being significantly low in SD-exposed squirrels. Our results suggest that even in tropical rodents seasonal variation in photoperiod is responsible for initiating female reproductive activities where circulatory melatonin via MT1R plays an important role.

KEYWORDS:

• Word
• photoperiod
• ovary
• steroidogenesis
• melatonin
• estrogen
• MT1

Acknowledgments

Financial support from University Grants Commission (UGC) as fellowship to Ms. Jayita Pal Chowdhury, annual (2015-2017) grants from DST-Purse Scheme (Department of Science and Technology, India,) UGC-CAS and UGC-UPE Scheme and equipment subsidiary award from Alexander von Humboldt foundation to Prof. C. Haldar are acknowledged. Dr. Soumik Goswami, Dr. Sameer Gupta and Mr. Debarshi Sarkar are acknowledged for their help during experimentation and data analysis.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the University Grants Commission (UGC) as fellowship to Ms. Jayita Pal Chowdhury and also annual (2015-2017) grants was provided from DST-Purse Scheme (Department of Science and Technology, India).