Mouse versus rat: Profound differences in meiotic regulation at the level of the isolated oocyte

Abstract

Cumulus cell-enclosed oocytes (CEO), denuded oocytes (DO) or dissected follicles were obtained 44–48 h after priming immature mice (20–23-days-old) with 5 IU or immature rats (25–27-days-old) with 12.5 IU of equine chorionic gonadotropin, and exposed to a variety of culture conditions. Mouse oocytes were more effectively maintained in meiotic arrest by hypoxanthine, dbcAMP, IBMX, milrinone, and 8-Br-cGMP. The guanylate cyclase activator, atrial natriuretic peptide, suppressed maturation in CEO from both species, but mycophenolic acid reversed IBMX-maintained meiotic arrest in mouse CEO with little activity in rat CEO. IBMX-arrested mouse, but not rat, CEO were induced to undergo germinal vesicle breakdown (GVB) by follicle stimulating hormone (FSH) and amphiregulin, while human chorionic gonadotropin (hCG) was ineffective in both species. Nevertheless, FSH and amphiregulin stimulated cumulus expansion in both species. FSH and hCG were both effective inducers of GVB in cultured mouse and rat follicles while amphiregulin was stimulatory only in mouse follicles. Changing the culture medium or altering macromolecular supplementation had no effect on FSH-induced maturation in rat CEO. The AMP-activated protein kinase (AMPK) activator, AICAR, was a potent stimulator of maturation in mouse CEO and DO, but only marginally stimulatory in rat CEO and ineffective in rat DO. The AMPK inhibitor, compound C, blocked meiotic induction more effectively in hCG-treated mouse follicles and heat-treated mouse CEO. Both agents produced contrasting results on polar body formation in cultured CEO in the two species. Active AMPK was detected in germinal vesicles of immature mouse, but not rat, oocytes prior to hCG-induced maturation in vivo; it colocalized with chromatin after GVB in rat and mouse oocytes, but did not appear at the spindle poles in rat oocytes as it did in mouse oocytes. Finally, cultured mouse and rat CEO displayed disparate maturation responses to energy substrate manipulation. These data highlight significant differences in meiotic regulation between the two species, and demonstrate a greater potential in mice for control at the level of the cumulus cell-enclosed oocyte.

Reversible meiotic arrest in feline oocytes

“…Feline oocytes also appeared to be highly sensitive to IBMX since 100 mM maintained the majority of oocytes at the GV stage, similar to observations in murine oocytes (Downs et al 1988;Downs 2011). This is in contrast to studies of bovine and porcine oocytes, in which much higher concentrations of IBMX (500 to 5000 mM) had less pronounced effects on meiosis (Bilodeau et al 1993;Fan et al 2002;Laforest et al 2005).…”

“…Other studies have reported 0 (Godard et al 2009) to 21% (Luvoni et al 2006) of feline oocytes undergoing spontaneous maturation and reaching MII, suggesting that other factors influence spontaneous maturation aside from the presence of gonadotrophins or growth factors. For example, the amount and type of metabolic substrates available in the culture medium influence the rate of spontaneous maturation in rodents and cattle in a species-specific manner (Bilodeau-Goeseels 2006;Downs 2011). In addition, intact COCs can consume a large amount of carbohydrates during in vitro maturation (Sutton-McDowall et al 2004;Herrick et al 2006b;Stokes et al 2008).…”

“…Both of these chemicals have been used extensively in multiple species with consistent, predicted effects (Bilodeau et al 1993;Fan et al 2002;Thomas et al 2002;Chen et al 2009;Downs 2011). In mice, rats, pigs, cattle, macaques and humans, the majority of PDE activity within the oocyte is due to PDE3, which is sensitive to IBMX (Downs et al 1989;Conti et al 1998;Richard et al 2001;Jensen et al 2002;Thomas et al 2002;Liang et al 2005;Nogueira et al 2006;Sasseville et al 2009).…”

Identification of phosphodiesterase 9A as a cyclic guanosine monophosphate–specific phosphodiesterase in germinal vesicle oocytes: a proposed role in the resumption of meiosis

“…The concentration of the cGMP isozyme, 8-Br-cGMP, needed in our experiments to completely inhibit PDE3A activity was much higher and non-physiologic, this is most likely due to the imidizole ring substitution, required to make the compound soluble and membrane permeable; this increases the IC 50 65-fold compared to unmodified cGMP (38). Although a higher dose is required to exert a similar effect as native cGMP, 8-Br-cGMP is widely used in oocyte meiosis studies and is a suitable model agent for in vitro experiments (39, 40). …”

Nutrient pathways regulating the nuclear maturation of mammalian oocytes

“…This action may be unique in the mouse, because it is the only species thus far tested where oocyte maturation is under positive control by AMPK. Indeed, stimulation of AMPK in cow, porcine and rat oocytes does not trigger meiotic resumption (Bilodeau-Goeseels et al 2007;Mayes et al 2007;Tosca et al 2007;Downs 2011).…”