| It has been reported that cumulus cells (CCs) play an important role in oocyte meioticmaturation, fertilization and embryo developmental potential in cattle, goat, pig and mouse,but few studies were conducted in rabbit. Previously, the reports in rabbit mainly focused onthe in vitro maturation of the cumulus-enclosed oocytes (CEOs), but the interactions betweenthe cumulus cells and oocyte haven't been investigated. As an important experimental animal,rabbit are often used in embryo engineering. The aim of the present study was to analyze theeffects of rabbit cumulus cells on the oocyte nuclear and ooplasmic maturation, oocytesurvival and degeneration. Cumulus oocyte complexes (COCs) and naked oocytes (NOs)were recovered directly from rabbit ovaries. Corona-enclosed oocytes (COs) and DOs(denuded oocytes) were obtained from COCs freed of part or whole CCs, and then the oocyteswere cultured in the following five ways. (1) CEOs were cultured alone; (2) COs werecultured alone; (3) DOs were co-cultured with COCs (DOs(COCs)); (4) DOs wereco-cultured with CCs (DOs(CCs)); (5) DOs were cultured alone. After the oocytes were invitro cultured 24 h or 30 h, the oocyte nuclear maturation was analyzed and compared. Thecleavage was used to evaluate the oocyte maturation quality after the nuclear matured oocyteswere parthenogenetically activated. The results were as the following. (1) The percentage ofnuclear maturation of CEOs, COs, DOs(COCs), DOs(CCs) and DOs was 76%, 46%, 13%,7% and 6% respectively after 24 h incubation, and the percentage of oocyte nuclearmaturation in the former four culture ways were all significantly different with each other(P<0.05). The Cleavage rate was 68%, 63%, 35%, 21% and 17% respectively afterpathenogentic activation, and the cleavage rate in the first two culture ways were significantlyhigher than that of the others (P<0.05). (2) The percentage of oocyte nuclear maturation were82%, 62%, 24%, 16% and 7% respectively after incubation 30 h and all of them hadsignificant difference with each other (P<0.05). The cleavage rate was 79%, 76%, 61%, 45%,and 28% respectively and the first two culture ways had significantly higher ooplasmicmaturaion rate than the others (P<0.05). (3) The nuclear maturation was significantlyimproved when the culture time of DOs(COCs) was prolonged from 24 h to 30 h (13% vs24%, P<0.05) and the cleavage was also improved significantly (35% vs 61%, P<0.05).DOs(CCs) nuclear maturation was significantly improved when the culture time wasprolonged from 24 h to 30 h (7% vs 16%, P<0.05), but the ooplasmic maturation was notimproved (P>0.05). (4) The percentage of nuclear maturation of NOs incubated with orwithout cumulus cells was both 2% after 24 h incubation (P>0.05). When the culture time wasprolonged from 24 h to 30 h, the nuclear maturation was not improved (P>0.05). (5) Theoocyte degeneration rate of COCs, COs, DOs(COCs), DOs (CCs) ) and DOs wassignificantly different with each others after 24 h incubation (7%, 23%, 44%, 64%, 73%,P<0.05) and after 30 h incubation (12%, 20%, 41%, 60%, 77%, P<0.05). There was nosignificant difference in oocyte degeneration in the same groups between 24 h and 30 hincubation (P>0.05). The results suggest that rabbit cumulus cells affect the oocyte nuclearand ooplasmic maturation, survival, and the prolongation of the culture time of rabbit oocytefrom 24 h to 30 h improves the ooplasmic maturation. Rabbit NOs have no meiotic potential,which cannot be improved by co-culture with dispersed cumulus cells. |
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