In vitro culture retards spontaneous activation of cell cycle progression and cortical granule exocytosis that normally occur in in vivo unfertilizedmouse eggs
Al. Abbott et al., In vitro culture retards spontaneous activation of cell cycle progression and cortical granule exocytosis that normally occur in in vivo unfertilizedmouse eggs, BIOL REPROD, 59(6), 1998, pp. 1515-1521
We have previously demonstrated that metaphase II-arrested eggs recovered f
rom oviducts at increasing times after hCG administration display a time-de
pendent spontaneous entry into anaphase, as well as release of cortical gra
nules (CGs) and the associated modifications of the zona pellucida (ZP), a
decrease in histone H1 and mitogen-activated protein kinase activities, and
the recruitment of maternal mRNAs [Xu et al., Biol Reprod 1997; 57:743-750
). These changes are correlated with the time-dependent increase in suscept
ibility of these eggs to undergo parthenogenetic activation. We report here
the effect of culture of ovulated eggs, retrieved 13 or 16 h post-hCG admi
nistration and cultured in vitro for various periods of time, on the aforem
entioned parameters of egg activation and cell cycle resumption. In contras
t to extended residence of the eggs in the oviduct, culture in vitro retard
ed cell cycle events associated with completion of the second meiotic reduc
tion and inhibited CG release and the associated modifications of the ZP, a
s well as the recruitment of maternal mRNAs. The retardation or inhibition
of these changes during in vitro culture resulted in eggs that were less su
sceptible to parthenogenetic activation than eggs that resided in the ovidu
ct for comparable time periods. Results of these experiments indicate that
egg culture in vitro (which likely occurs under suboptimal conditions) inhi
bits, rather than accelerates, the progression into the interphase-like sta
te as compared to that seen in eggs residing in the oviduct for increasing
periods of time. These results also suggest that, for studies focused on in
vitro fertilization or egg activation, the ovulated eggs should be placed
under appropriate in vitro conditions as soon as possible.