Analyses of Developmental Ability of (BALB/c × C57BL/6) F₁ and ICR Mouse Embryos Fertilized In Vitro and Their Chromosome at the First Cleavage Division

抄録

Superovulated eggs in (BALB/c×C57BL/6) F₁ and ICR (outbred in a closed colony) female mice were fertilized in vitro with spermatozoa obtained from caudal epididymides of ICR males. Air-dried chromosome preparations were made from colcemid-primed 1-cell eggs and stained by the C-banding method. The fertilization rate was lower in F₁ eggs than in ICR eggs (88 vs. 92%, P<0.02). The incidence of metaphase ("syngamy") eggs was higher in F₁ eggs, and the incidence of pronuclear and late prometaphase ("pre-syngamy") eggs was higher in ICR eggs (P<0.001, P<0.005), showing delayed progress of the first cleavage in the ICR eggs. Developmental rates from 2-cell to 4-cell stage and from morula to blastocyst stage were significantly lower in ICR eggs (P<0.001) than in F₁ eggs. These results show that a delay of embryo development had already appeared before male and female genomes fused (pre-syngamy). The incidence of triploidy, which might be caused by dispermy, was higher in F₁ eggs, in both the pronuclear and mitotic stages (P<0.001). A little aneuploidy and structural aberration of chromosomes occurred in both F₁ and ICR eggs, and no significant difference was observed between F₁ and ICR eggs. The sex ratio at the first cleavage stage in both F₁ and ICR eggs showed no significant deviation from equality.