Human Reproduction, Vol 12, 2781-2783, Copyright © 1997 by Oxford University Press
GI Perez and JL Tilly
Recent studies with female ICR mice have suggested that oocyte DNA
fragmentation is one reason for poor oocyte quality and lower fertility
associated with ageing. Since it was not determined if this increased
'apoptotic' potential in aged oocytes is due to changes within the oocyte
itself or within the microenvironment of cumulus cells (CC) surrounding the
germ cell, we sought to clarify if CC were required to affect the rate of
apoptosis in oocytes maintained in vitro. Intact cumulus-oocyte complexes
(COC) were retrieved by superovulation of virgin female ICR mice at 7 weeks
('young') or 34-35 weeks ('aged') of age. One-half of the COC in each group
were incubated at 37 degrees C in human tubal fluid medium under paraffin
oil for 24 h. The other half of the COC in each group were denuded of CC
and incubated under the same conditions (denuded oocytes; DO). Following
incubation, COC were stripped of adherent CC by gentle pipetting. All DO
were then fixed and checked by light microscopy for morphological changes
characteristic of apoptosis. In young mice, the presence of CC had no
significant effect on oocyte death rate (18 +/- 9% and 14 +/- 6% apoptotic
oocytes in COC and DO, respectively; P > 0.05). However, in aged mice
the percentage of CC-enclosed oocytes that underwent apoptosis was
significantly greater as compared to the death rate in DO (48 +/- 3% versus
19 +/- 8% apoptotic oocytes, respectively; P < 0.05). This increased
death potential was due to the presence of CC since the occurrence of
apoptosis in DO of aged versus young mice was not significantly different
(19 +/- 8% versus 14 +/- 6% apoptotic oocytes, respectively; P > 0.05).
These results demonstrate that the age-dependent acceleration of apoptosis
in oocytes maintained in vitro requires the CC.
ARTICLES
Cumulus cells are required for the increased apoptotic potential in oocytes of aged mice
Vincent Center for Reproductive Biology, Department of Obstetrics and Gynecology, Massachusetts General Hospital/Harvard Medical School, Boston 02114, USA.
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