Quantification of Estradiol 17β (Erβ) Receptor Gene in Cultured and in vivo Grown Ovarian Follicles of Sheep

Background: The study aimed at quantifying the estradiol 17 β receptor gene in in vivo developed and cultured ovarian follicles of sheep in different culture media by RT-q PCR. Since, estradiol 17 β is a key steroid hormone for antrum formation, preovulatory follicle maturation, expression of genes involved in ovarian differentiation and follicular rupture during ovulation of mammals and the local action of any hormone on the target cell or tissue depends on the expression of its receptor. Methods: Estradiol 17β receptor mRNA expression in sheep oocytes and cumulus cells was studied using quantitative RT-PCR for: (i) In vivo grown preantral, early antral, antral, large antral follicles and cumulus-oocyte complexes (COCs) obtained from large antral follicles subjected to 24 h of in vitro maturation and (ii) Accordingly, the cumulus cells and oocytes were collected from different development stages of preantral follicles cultured in vitro in TCM199B (Group I), TCM199B +E2 (5 ng/mL) (Group II) and Standard medium + E2 (5 ng/mL) (Group III) for 3 min, two, four or six days and subsequently matured in vitro for 24 h. Result: Estradiol 17 β receptor was observed at all stages of ovarian follicles in both cumulus cells and oocytes. The upregulation of the ER β gene was noted as the follicle grew in both the media supplemented with estradiol 17 β. Irrespective of in vitro groups, cumulus cells from COCs of the large antral follicles matured in vitro for 24 h exhibited the highest gene expression of the estradiol 17 β receptor. Among the three groups under study, the follicular cells of PFs’ cultured in group III showed the highest expression of the ERβ gene at any point of their development. The supplementation of estradiol 17 β in low doses stimulated synergism with growth factors and hormones to express its receptors in cultured preantral follicles of sheep.