Do insulin-like growth factors play a role in final follicular maturation: Superovulation as a test model

Abstract

Mouse oocytes can be obtained via superovulation or using in vitro maturation although several factors, including genetic background, may affect response. Our previous studies have identified various mouse species as models to understand the role of sexual selection on the evolution of sperm traits and function. In order to do comparative studies of sperm–oocyte interaction, we sought reliable methods for oocyte superovulation and in vitro maturation in mature females of three mouse species (genus Mus). When 5 IU pregnant mare's serum gonadotrophin (PMSG) and 5 IU human chorionic gonadotrophin (hCG) were injected 48 h apart, and oocytes collected 14 h post-hCG, good responses were obtained in Mus musculus (18 ± 1.3 oocytes/female; mean ± S.E.M.) and Mus spretus (12 ± 0.8), but no ovulation was seen in Mus spicilegus. Changes in PMSG or hCG doses, or longer post-hCG intervals, did not improve results. Use of PMSG/luteinizing hormone (LH) resulted in good responses in M. musculus (19 ± 1.2) and M. spretus (12 ± 1.1) but not in M. spicilegus (5 ± 0.9) with ovulation not increasing with higher LH doses. Follicular puncture 48 h after PMSG followed by in vitro maturation led to a high oocyte yield in the three species (M. musculus, 23 ± 0.9; M. spretus, 17 ± 1.1; M. spicilegus, 10 ± 0.9) with a consistently high maturation rates. In vitro fertilization of both superovulated and in vitro matured oocytes resulted in a high proportion of fertilization (range: 83–87%) in the three species. Thus, in vitro maturation led to high yields in all three species. These results will allow future studies on gamete interaction in these closely related species and the role of sexual selection in gamete compatibility.