Domestic cat oocytes are seasonally sensitive to follicle-stimulating hormone (FSH). Compared to those collected during the breeding season, oocytes from the non-breeding season require more FSH during in vitro maturation to achieve comparable developmental competence. The present study tested the hypothesis that this seasonal variation was due to altered expression of FSH receptors (FSHR) and/or FSH-induced genes. Relative expression levels of FSHR mRNA and FSH-enhanced gene estrogen receptor β (ESR2) were measured by qPCR in whole ovaries and immature cumulus-oocyte complexes (COCs) isolated from cat ovaries during the natural breeding versus non-breeding seasons. Expression levels of FSH-induced genes prostaglandin-endoperoxidase synthase 2 (PTGS2), early growth response protein-1 (EGR1) and epidermal growth factor receptor (EGFR) were examined in mature COCs from both seasons that were (a) recovered in vivo or (b) matured in vitro with conventional (1 µg ml-1) or high (10 µg ml-1) FSH concentrations. Overall FSHR mRNA levels were lower in whole ovaries during the non-breeding compared to breeding season, but were similar in immature COCs; whereas ESR2 levels did not differ in either group between seasons. We observed changes in PTGS2, EGR1 and EGFR mRNA expression patterns across maturation in COCs within, but not between the two seasons. The lack of seasonal differentiation in FSH-related genes was not consistent with the decreased developmental capacity of oocytes fertilized during the non-breeding season. We conclude that the seasonal decrease in oocyte sensitivity to FSH occurs both in vivo and in vitro and is unrelated to changes in expression of FSHR mRNAs or mRNA of FSH-induced genes in COCs from antral follicles.
