Gene expression profiling of melatonin receptor subtypes in the ovarian hierarchical follicles of the Sichuan white goose.

Melatonin (N-acetyl-5-methoxytryptamine), an indole hormone, regulates a variety of important central and peripheral actions related to circadian rhythms and reproduction through its specific receptor subtypes (Mel-1a, Mel-1b and Mel-1c). However, the expression profile of melatonin receptor genes (MTNR1A, MTNR1B and MTNR1C) in ovarian hierarchical follicles of geese remains to be clarified. In this study, the expression level of melatonin receptors in small white follicle (SWF), small yellow follicle (SYF), the largest follicle (F1), second largest (F2), third largest (F3), fourth largest (F4), fifth largest (F5), and postovulatory follicle (POF) in the Sichuan white goose were examined using quantitative real-time PCR (qRT-PCR). The results showed that the expression levels of MTNR1A, MTNR1B and MTNR1C initially increased and later decreased. The highest levels of gene expression of these receptor subtypes were observed in F5 or F4 in all examined follicles. Furthermore, the expression of MTNR1A and MTNR1B mRNA was significantly greater in SYF compared with SWF (P<0.05), but MTNR1C was absent in SWF. The expression of MTNR1A, MTNR1B and MTNR1C mRNA was significantly greater in F5 compared with SYF (P<0.05), and the expression of MTNR1A and MTNR1C mRNA was higher in F1 compared with POF (P<0.05). In addition, the oestrogen concentration in SWF, SYF, F4, F3, F2, F1 and POF was measured using ELISA. The oestrogen concentration and melatonin receptor expression both were initially observed to increase and subsequently decrease. The oestrogen concentration in F4 and F3 was highest in all examined samples and was 1318.2pg/g and 1318.1pg/g, respectively. These results suggest that the melatonin receptor may be involved in the activation of the SWF and SYF to allow the SWF and SYF to develop into the subsequent follicles. Furthermore, follicles and the expression of the melatonin receptors may be regulated by the secretion of the oestrogen.