Adenylyl cyclases in oocyte maturation: A characterization of AC isoforms in bovine cumulus cells

Abstract

Mammalian oocytes are arrested at the G(2)/M transition in the meiotic cell cycle. It is well known that a decrease in intraoocyte cAMP concentrations accompanies resumption of meiosis, but the precise trigger of this decrease remains a mystery. Follicular somatic cells are intimately coupled to the oocyte and are thought to transmit maturation signals to the oocyte in response to hormonal stimulation. Here, we investigate the nature of the follicular somatic cell response to hormonal stimulation by identifying and characterizing the adenylate cyclase isoforms present in bovine cumulus cells. RT-PCR and Western blot analysis revealed the presence of multiple adenylyl cyclase isoforms in bovine granulosa and cumulus cells. Pharmacological manipulation of the AC isoforms showed that multiple isoforms were indeed active. Our data indicate that the PKC inhibited adenylate cyclases IV and VI and the calcium-stimulated isoform I predominate in bovine cumulus cells.

Ca2+ signaling during maturation of cumulus–oocyte complex in mammals

“…LH‐induced Ca 2+ rises are biphasic as a result of the cumulative contribution of Ca 2+ influx and intracellular Ca 2+ mobilization (Davis et al, 1987; Alila et al, 1989; Mattioli et al, 1990) (unpublished data). Studies in bovine COCs demonstrated that the LH‐induced [Ca 2+ ] i rise causes [cAMP] i elevation in cumulus cells by activating Ca 2+ ‐sensitive adenylate cyclases; in particular, the activity of adenylate cyclase I seems to be stimulated by [Ca 2+ ] i rises resulting from Ca 2+ influx (Lastro et al, 2006). In rodent oocytes, on the other hand, Ca 2+ is able to inactivate all the three adenylyl cyclases identified, and this leads to a drop of [cAMP] i (Hanoune and Defer, 2001; Wang and Storm, 2003).…”

Reversible meiotic arrest in feline oocytes

“…These differences between species are likely to be related to differences in adenylate cyclase and PDE activity within the oocyte. In most species, exposure to gonadotrophins or forskolin increases production of cAMP within the cumulus cells, which activates type II protein kinase A (PKA) and stimulates cumulus expansion (Bornslaeger and Schultz 1985;Downs and Hunzicker-Dunn 1995;Thomas et al 2002;Lastro et al 2006). Increased cAMP production and activation of type II PKA within the cumulus cells can also lead to the resumption of meiosis, but this stimulatory effect is dependent on the concentration of cAMP and the associated activity of type I PKA within the oocyte (Downs and Hunzicker-Dunn 1995).…”

“…It may be that oocytes are highly sensitive to cAMP and even small changes in intracellular concentrations of cAMP that are not statistically significant can have biologically significant effects on the oocyte. Detecting these subtle differences may be further complicated by the large variability in COC quality and cAMP content when oocytes or cumulus cells are recovered from follicles at different stages of maturation (Lastro et al 2006;Bagg et al 2009;Sasseville et al 2009). Finally, it is necessary to maintain cAMP concentrations within the oocyte during sample collection and processing before the assay.…”

“…By inhibiting PDE3 activity, IBMX maintains meiotic arrest by preventing a decline in cAMP concentrations within the oocyte after recovery (Schultz et al 1983;Luciano et al 2004;Albuz et al 2010) or permitting the accumulation of cAMP produced by intra-oocyte adenylate cyclase(s) (Mehlmann 2005). Although forskolin-sensitive adenylate cyclases are present in both cumulus cells and oocytes (Horner et al 2003;Lastro et al 2006), forskolin increases intracellular cAMP concentrations within cumulus cells, with little or no change in cAMP concentrations within denuded oocytes in mice (Bornslaeger and Schultz 1985), rats (Racowsky 1984), hamsters (Racowsky 1985a), pigs (Racowsky 1985b) or cattle (Bilodeau et al 1993;Thomas et al 2002). However, forskolin can increase cAMP concentrations within oocytes if the gap-junctional communication between the oocyte and cumulus cells is maintained during forskolin exposure (Racowsky 1984(Racowsky , 1985a(Racowsky , 1985bBornslaeger and Schultz 1985;Bilodeau et al 1993;Thomas et al 2002).…”

The Control of Meiotic Arrest and Resumption in Mammalian Oocytes

“…Taken together, these results indicate that bovine oocytes and cumulus cells may contain AC isoforms with different sensitivities to Mn 2+ . Lastro et al, (2006) determined that bovine cumulus cells obtained from follicles 2-8 mm contained mRNA for AC isoforms 1, 3, 4, 6, and 9 and were enriched in PKC-inhibited isoforms 4 and 6 and the Ca 2+ -stimulated isoform 1. However, the AC isoforms of bovine oocytes have not yet been determined.…”