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Effect of pre-incubation of porcine COCSs in medium without gonadotropins on the chromatin configuration and quality of oocytes matured in vitro

SUN Xing-Shen① YUE Kui-Zhong① LI Jia-Lin① ZOU Yi① and TAN Jing-He ②** (①College of Life Science, Northeast Agricultural University, Harbin 150030, China) (②College of Animal Science and Technology, Shandong Agricultural University, Tai'an 217018, China)  
Although porcine oocytes matured and fertilized in vitro can develop to blastocyst stage, the rate of development is still low.Culture conditions and the heterogeneity of oocytes before culture may affect the quality of oocytes matured in vitro.The effect of pre-incubation of cumulus-oocyte complexes(COCs)in medium without gonadotropins on chromatin configuration and quality of porcine oocytes matured in vitro was, therefore, investigated in this experiment.Ovaries were collected from a local slaughterhouse, and the COCs were aspirated from 2~6 mm follicles on the ovarian surface and classified into A, B and C categories in accordance with cumulus morphology.Oocytes were cultured in TCM-199 supplemented with 10% FCS and 10% porcine follicular fluid, PMSG and hCG were added depending on experimental designs.Nuclear maturation and GV chromatin configuration of oocytes was evaluated by orecin and Hochest 33342 staining, respectively.The major findings are as follows: 1.the morphology of polar bodies in in vitro matured(IVM)oocytes varied and four types of oocytes could be distinguished, i.e.those with intact, degenerated, fragmented and no polar bodies.2.When type A oocytes were pre-cultured in the absence of gonadotropins for 12 hours, the proportion of germinal vesicle stage(GV-1) oocytes decreased significantly compared to those cultured in the presence of these hormones(48.2% vs.27.1%, P0.05), but the proportion of GV-3 oocytes increased markedly(19.6% vs.50.8%).3.The proportion of oocytes with intact polar bodies after maturation was significantly higher when they were pre-cultured without hormones than when pre-cultured with hormones(59.6% vs.27.5%).Together, these results indicate that a delayed exposure of porcine COCs to gonadotropins led to an improved quality and a more synchronized development of oocytes matured in vitro [Acta Zoologica Sinica 49(1):86-90, 2003].
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