Genetic and epigenetic factors affecting blastomere fragmentation in two-cell stage mouse embryos

We report here that mouse embryos can exhibit a significant incidence of bl astomere fragmentation at the two-cell stage. The incidence of this is infl uenced by both the maternal and paternal genotype. Embryos from C57BL/6 mot hers exhibit a very low incidence of fragmentation at the two-cell stage in crosses involving males of C57BL/6, DBA/2, AKR/J, or SJL strains but exhib it a significantly increased incidence of fragmentation in crosses involvin g C3H/HeJ males. Increased fragmentation is seen in embryos from C3H/HeJ fe males crossed with C57BL/6 males but not with C3H/HeJ males. Embryos obtain ed from reciprocal (C57BL/6 X C3H/HeJ) F-1 hybrid females also exhibit an i ncreased incidence of fragmentation at the two-cell stage when the hybrid f emales are mated to either C57BL/6 or C3H/HeJ males. Interestingly, the res ults differ significantly between reciprocal F-1 hybrid females, indicating a parental origin effect, possibly a result of either genomic imprinting o r differences in mitochondrial origin. We conclude that the incidence of bl astomere fragmentation at the two-cell stage in the mouse is under the cont rol of more than one genetic locus. We also conclude that blastomere fragme ntation is affected by both parental genotypes. These results are relevant to understanding the genetic control blastomere fragmentation, which may co ntribute to evolutionary processes, affect the success of procedures such a s cloning, and affect the outcome of assisted reproduction techniques.