Kisspeptin stimulates sheep ovarian follicular development in vitro through homologous receptors.

The present study was conducted to elucidate (1) the influence of kisspeptin (KP) on the in vitro development of preantral follicles (PFs) and (2) evolution of KP receptor gene (KISS1R) expression during ovarian follicular development in sheep. Kisspeptin was supplemented (0-100 µg/ml) in the culture medium of PFs for 6 days. The cumulus-oocyte complexes (COCs) from cultured PFs were subsequently matured to metaphase II (MII) for an additional 24 h. The proportions of PFs exhibiting growth, antrum formation, average increase in diameter, and maturation of oocytes to MII stage were the indicators of follicular development in vitro. The expression of the kisspeptin receptor gene at each development stages of in vivo developed (preantral, early antral, antral, large antral and COCs from Graafian follicles) and in vitro cultured PFs supplemented with KP was assessed using a real-time polymerase chain reaction. The best development in all the parameters under study was elicited with 10 µg/ml of KP. Supplementation of KP (10 µg/ml) in a medium containing other growth factors (insulin-like growth factor-I) and hormones (growth hormone, thyroxine, follicle-stimulating hormone) resulted in better PF development. The KISS1R gene was expressed in follicular cells and oocytes at all the development stages of both in vivo developed and in vitro cultured follicles. Higher KISS1R gene expression was supported by culture medium containing KP along with other hormones and growth factors. Accordingly, it is suggested that one of the mechanisms through which KP and other growth factors and hormones influence the ovarian follicular development in mammals is through the upregulation of expression of the KP receptor gene.

Kisspeptin promotes follicular development through its effects on modulation of P450 aromatase expression and steroidogenesis in sheep ovarian follicles.

The present study was conducted to ascertain whether the role of kisspeptin in promoting in vitro development of preantral follicles was through the regulation of P450 aromatase gene expression and steroidogenesis in sheep. Accordingly, the cumulus cells and oocytes were collected from different development stages of preantral follicles grown in vivo and cultured in vitro in TCM199B (Group I), TCM199B + KP (10 µg/mL) (Group II) and Standard medium + KP (10 µg/mL). To measure the steroid (Estradiol-17ß; E2 and Progesterone; P4 ) synthesis through ELISA, spent culture medium was collected separately from the same in vitro groups. E2 synthesis in the spent medium collected from all the three groups showed an increasing trend from PFs' exposed to respective culture media for 3 min to 2-day culture stage but decreased thereafter till 6-day culture stage. This is followed by a sharp increase in E2 concentration in the spent medium collected after in vitro maturation. However, P4 synthesis in group III followed increased pattern as the development progressed from PFs' exposed to culture medium for 3 min to in vitro maturation stage. The steroid production was observed at all stages of in vitro development in altered supplemented conditions. The steroid synthesis in the spent medium was highest in the 6 day cultured PFs' in Standard medium + KP matured in vitro for 24 h. Therefore, supplementation of kisspeptin along with other growth factors promoted steroid production in cultured preantral follicles far better than in other media.

Quantitative expression patterns of GDF9 and BMP15 genes in sheep ovarian follicles grown in vivo or cultured in vitro.

Quantitative patterns of expression of the growth differentiation factor 9 (GDF9) and bone morphogenic protein 15 (BMP15) genes in different development stages of in vivo and in vitro grown ovarian follicles in sheep were studied for the first time. Both GDF9 and BMP15 were expressed in the cumulus cells and oocytes at all the development stages of in vivo and in vitro grown ovarian follicles. Growth differentiation factor 9 and bone morphogenic protein 15 exhibited stage-specific undulations in the expression in the cumulus cells and oocytes isolated from in vivo grown ovarian follicles. These undulations could be related to discrete development events during the ovarian follicle development. The expression of GDF9 and BMP15 was highest (3.38 ± 0.02 and 2.69 ± 0.06, respectively; P ≤ 0.05) in the primordial follicles compared with preantral, early antral, antral, and large antral stages. Similarly, GDF9 and BMP15 expression in the cumulus cells (0 ± 0.16 and 0 ± 0.07) and oocytes (1.47 ± 0.07 and 1.32 ± 0.03) was lowest (P ≤ 0.05) in the in vivo grown antral follicles. In the cultured follicles, the stage-specific undulations observed in the expression of GDF9 and BMP15 in the in vivo grown follicles were either different or abolished. For example, in the oocytes from in vitro grown follicles, the expression of BMP15 did not change as the development progressed all the way from preantral to large antral follicle stage although in the oocytes from in vivo grown follicles BMP15 expression exhibited stage-specific variations. It is concluded that GDF9 and BMP15 follow a stage-specific pattern of expression during the in vivo development of ovarian follicles in sheep, and in vitro culture altered the stage-specific changes in the expression of these two genes.

Effect of leptin on in vitro development of ovine preantral ovarian follicles.

The influence of human or ovine leptin on in vitro culture of preantral follicles (PFs) isolated from sheep ovaries was investigated. Among the 12 different concentrations (0-1000 ng/mL) of human leptin tested, proportion of PFs exhibiting growth, mean increase in diameter, antrum formation, and maturation of the oocytes to MII stage were the best in 10 ng/mL. Culture of sheep ovarian PFs in TCM 199 supplemented with 10 ng/mL of human or ovine leptin FSH (2.5 µg/mL), thyroxine (1 µg/mL), insulinlike growth factor I (10 ng/mL), and GH (1 mIU/mL) resulted in significantly (P ≤ 0.05) greater average increase in diameter (11 and 9 vs. 6 µm), better proportions of PFs exhibiting growth (66% and 58% vs. 48%), antrum formation (51% and 51% vs. 34%), and maturation of oocytes to MII stage (24% and 22% vs. 7%) than the control medium. It is concluded that (1) the optimum dose of leptin for the growth of sheep PFs in vitro was 10 ng/mL, (2) human or ovine leptin supported similar development in vitro of PFs in sheep, (3) inclusion of leptin along with FSH, thyroxine, insulinlike growth factor I, and GH resulted in only a marginal further improvements in in vitro development of sheep PFs'.

Quantitative expression of antiapoptotic and proapoptotic genes in sheep ovarian follicles grown in vivo or cultured in vitro.

To test the hypothesis that the poor development of the oocytes in cultured ovarian follicles of mammals is due to aberrant expression of developmentally important genes, quantitative expression patterns of Bcl2 (B-cell leukemia/lymphoma 2; antiapoptotic) and Bax (Bcl2-associated X protein; proapoptotic) genes in preantral, early antral, antral, large antral follicles, and cumulus-oocyte complexes (COCs) grown in vivo or cultured in vitro were studied. The level and pattern of expression of Bcl2 in the cumulus cells isolated from different development stages of in vivo- and in vitro-grown ovarian follicles were similar suggesting that in vitro culture did not alter the expression of this antiapoptotic gene in the cumulus cells. However, between the in vivo- and in vitro-grown ovarian follicles (1) Bcl2 expression levels in the oocytes from antral follicles (2.21 ± 0.14 vs. 0.87 ± 0.19), large antral follicles (0 ± 0.35 vs. 1.56 ± 0.13), and COCs (0.45 ± 0.31 vs. 2.69 ± 0.15), Bax expression levels in the (2) cumulus cells from early antral (2.09 ± 0.11 vs. 0.98 ± 0.13) and large antral follicle (0.63 ± 0.44 vs. 0 ± 0.21), and (3) oocytes from antral follicles (1.65 ± 0.20 vs. 0.97 ± 0.15), large antral follicles (0.93 ± 0.18 vs. 2.08 ± 0.11), and COCs (1.03 ± 0.17 vs. 2.09 ± 0.11) were significantly different (P ≤ 0.05). Similarly, Bcl2 to Bax ratios were also significantly different between some but not all stages of in vivo and in vitro development. From the present results, it is concluded that imbalance in the expression of proapoptotic and antiapoptotic genes may be an important cause for the compromised development potential of the oocytes in cultured ovarian follicles of sheep.