Meiotic abnormalities in in vitro-matured marmoset monkey (Callithrix jacchus) oocytes: development of a non-human primate model to investigate causal factors.

BACKGROUND: Meiotic abnormalities are thought to be a major causal factor of low embryo development rates, for embryos developed from in vitro-matured oocytes. A new non-human primate model, in the common marmoset, is being developed to facilitate investigation of the mechanisms involved.
METHODS: Oocytes were dissected from antral follicles from three size classes. They were allowed to mature in vitro for only 24 h, in order to focus the investigation on the rapidly maturing oocytes. Chromosome spreads were visualized with Giemsa staining, and spindles /chromosomes with fluorescently labelled anti-alpha-tubulin antibody combined with a DNA fluorochrome.
RESULTS: 40% of the oocytes had reached metaphase II (MII) after 24 h. Of the MII oocytes selected for karyotyping, readable chromosomal spreads were obtained from 64%. Overall, 63% of these presented a normal haploid chromosome number of 23,X, with all abnormal karyotypes occurring in the oocytes from small follicles. For another group of MII oocytes, where meiotic spindles were visualized, only half of the MII oocytes displayed well-formed spindles and apparently correct chromosomal alignment.
CONCLUSIONS: This work provides the first information on the normal and aneuploid MII meiotic chromosome sets for the marmoset oocyte, and demonstrates a high rate of chromosomal and spindle abnormality among rapidly maturing oocytes from small antral follicles.