Cytogenetic analysis of pig oocytes matured in vitro
McGaughey, R.W.; Polge, C.
Journal of Experimental Zoology 176(4): 383-395
Primary oocytes from the ovaries of prepubertal pigs were removed from small follicles and incubated in a defined culture medium for various periods of time. Evidence was obtained that the oocytes were delayed at diakinesis-metaphase I. When recovered after 42.5-55 hr of culture, 55% of oocytes had reached metaphase II. Of 56 cultured oocytes whose chromosomes were analysed at metaphase I, only one exhibited a chromosomal aberration (19 bivalents + 3 fragments), and one contained 18 bivalents+ 2 monovalents. Of 123 oocytes analysed at anaphase I, telophase I and metaphase II, 27% exhibited chromosomal abnormalities such as heteroploidy, fragments, chromosomal bridges, tripolar spindles and lagging chromosomes. In addition, 31% of 128 oocytes at metaphase II displayed degenerate chromosomes. Of 232 immature oocytes cultured for 42.5-55 hr, only about 20% could be regarded as chromosomally normal, mature secondary oocytes. The delay at diakinesis-metaphase I may be related to a failure of the granulosa cells to supply some substance required by the oocytes.