Development in vitro of preimplantation embryos from 55 mouse strains

Mouse pronuclear embryos were obtained by in vitro fertilization with oocytes of 55 strains of immature females by gonadotrophin-induced ovulation and epididymal sperm of Slc:ICR strain. The number of oocytes ovulated with hormones (5.3-49.4 oocytes per head; average, 22.6), rates of in vitro fertilization (12.2-95.3%; average, 70.7%) and subsequent preimplantation development in Whitten's medium (WM) varied greatly among strains. F1 hybrids developed significantly better than other strains of mice and outbred animals did not develop as well as inbred animals. Within inbred mice, coat colour had no significant effect. In addition, the observation of preimplantation development in WM supplemented with ethylenediamine tetraacetic acid (EDTA) showed that the beneficial effect of the chelator was not universal to mouse embryos; EDTA had a good effect on ICR and PW/aSlc embryos but not on AKR or ddY embryos. The results indicate that strain differences should be considered when interpreting reproductive experiments using mouse embryos.