Cytogenetic analysis of embryos generated from in vitro matured mouse oocytes reveals an increase in micronuclei due to chromosome fragmentation

Purpose: (i) To determine the prevalence of micronuclei in the cytoplasm of embryos generated from in vitro matured oocytes. (ii) Assess whether micronuclei presence are the result of chromosome fragmentation or the loss of whole chromosomes. Methods: In vitro fertilization was performed on mature oocytes generated from superovulated mice (control) and in vitro matured mouse oocytes. Fertilized oocytes were cultured to the two-cell stage and fixed to slides. Micronuclei assessment was performed after staining with Giemsa. Centromere assessment was made using immunofluorescent staining (CREST) of the centromeric kinctochores. Results: Micronuclei were observed in 2% (4/197) of control two-cell embryos and 36.2% (46/127) of two-cell embryos generated from in vitro matured oocytes (P < 0.02). Centromeres were not detected in micronuclei from either group. Conclusions: A significant increase in micronuclei was observed in embryos generated from in vitro matured oocytes. The lack of accompanying centromeres would suggest the micronuclei are the result of chromosome fragmentation.