Cleavage Speed and Blastomere Number in DBA/2J Compared with C57BL/6J Mouse Embryos.

DBA/2J mice are among the oldest and most important inbred strains still used in many research fields. However, this strain has reproductive problems, which may consume considerable time and effort during experiments requiring a large population. Because the quality of DBA/2J embryos has not yet been described in detail, we compared DBA/2J mice with the reproductively efficient C57BL/6J strain. Compared with C57BL/6J embryos, DBA/2J embryos had a slower cleavage speed (mean ± 1 SD; first cleavage: C57BL/6J, 16.87 ± 1.32 ; DBA/2J, 19.64 ± 0.96 h; P < 0.01; second cleavage: C57BL/6J, 41.12 ± 2.02 h; DBA/2J, 46.20 ± 2.68 h, P < 0.01) and lower cell counts at the morula and blastocyst stages (morula stage: C57BL/6J, 15 ± 3 cells per embryo; DBA/2J, 9 ± 5 cells per embryo; P < 0.05; blastocyst stage: C57BL/6J, 52 ± 6 cells per embryo; DBA/2J, 35 ± 14 cells per embryo; P < 0.05). In addition, the results of reciprocal in vitro fertilization and male-female reciprocal crosses revealed that these phenotypes were not affected by the sperm genome and were recessively inherited. These findings likely will facilitate the production of DBA/2J mice and genetically modified mice with their background. Our results also suggest that, due to their slow cleavage speed, DBA/2J mice can serve as a new model for human infertility.