Differential ovarian expression of KiSS‐1 and GPR‐54 during the estrous cycle and photoperiod induced recrudescence in Siberian hamsters ( Phodopus sungorus )

Kisspeptins, coded by the KiSS‐1 gene, regulate aspects of the reproductive axis by stimulating GnRH release via the G protein coupled receptor, GPR54. Recent reports show that KiSS/GPR54 may be key mediators in photoperiod‐controlled reproduction in seasonal breeders, and that KiSS‐1/GPR54 are expressed in the hypothalamus, ovaries, placenta, and pancreas. This study examined the expression of KiSS‐1/GPR54 mRNA and protein in ovaries of Siberian hamsters ( Phodopus sungorus ). Ovaries from cycling hamsters were collected during proestrus (P), estrus (E), diestrus I (DI), and diestrus II (DII). To examine KiSS‐1/GPR54 during stimulated recrudescence, additional hamsters were maintained either in long day (LD 16L:8D, control) or short day (SD 8L:16D) for 14 weeks and then transferred to LD for 0–8 weeks. Staining of KiSS‐1/GPR54 protein was detected by immunohistochemistry in steroidogenic cells of pre‐antral and antral follicles, and corpora lutea. Immunostaining peaked in P and E, but decreased in the diestrus stages ( P  < 0.05). In recrudescing ovaries, KiSS‐1/GPR54 immunostaining was low after 14 weeks of SD exposure (post‐transfer [PT] week 0), and increased during the early weeks of recrudescence. Expression of KiSS‐1/GPR54 mRNA was low with short day exposure, but increased during recrudescence and was higher at PT week 8 as compared to PT weeks 0 and 2 ( P  < 0.05). The elevated KiSS‐1/GPR54 expression during P and E suggests a potential role in ovulation in Siberian hamsters. Transient increases in KiSS‐1/GPR54 expression following LD stimulation are also suggestive of possible involvement in ovulation and/or restoration of ovarian function. Mol. Reprod. Dev. 76: 444–452, 2009. © 2008 Wiley‐Liss, Inc.