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Abstract
The present study was designed to address the
physiological role played by cAMP on gap junction (GJ)
mediated communications between oocyte and cumulus cells
during in vitro maturation. cAMP was stimulated by
different collection and maturation media known to induce
different rates of nuclear maturation and developmental
competence as well as different levels of cumulus
expansion. Cumulus-oocyte complexes (COCs) were matured
for 0, 3, 7, 12, 18 and 24 h in the absence of
stimulation or in the presence of serum and gonadotropins
(FCS+hMG) or 0.01 µg/ml of invasive Adenilate Cyclase
(iAC). For each time point, intracellular cAMP
concentration ([cAMP]i) was determined either in the
whole COC and oocyte after cumulus cells removal. GJ
functional status was analyzed by microinjection of
Lucifer yellow fluorescent dye in cumulus-enclosed
oocytes and by immunohistochemical localization of
connexin 43 (Cx43). In the absence of stimulation, [cAMP]
i in COC and oocyte was lower than in other groups and
communications declined after 3h of culture. In FCS+hMG
group [cAMP]i increased significantly in COC, with a peak
between 3 and 7 h that was temporally correlated with the
beginning of cumulus expansion process, which occurred
only in this group, and with the termination of the
communications. COC matured in the presence of iAC showed
a moderate increase of [cAMP]i during all the maturation
time and a prolongation of oocyte-cumulus cell
communications. The immunohistochemical localization of
Cx43 confirmed the delay in connexons protein turnover in
iAC treated COCs. Our results show that cumulus expansion
and oocyte developmental competence are induced by
different levels of cAMP and that its intracellular
concentration may affect cell coupling between oocyte and
cumulus cells. We hypothesize that the higher
developmental competence of COCs matured in presence of
iAC could be achieved through a moderate increase of
intracellular cAMP which in turn determines a
prolongation of communications between the two cell types.
Key words:
Gamete Biology •
Cumulus cells •
Cyclic adenosine monophosphate •
Oocyte development
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