In vitro development of one-cell embryos from outbred mice: influence of culture medium composition

One-cell embryos from outbred mice (CF1, CD-1, and Dub:ICR) were cultured in various modifications of egg culture medium (ECM). The best development was observed in medium in which inorganic salts of modified T6 medium (mT6) replaced those of ECM. In this modification (TE), 66% of one-cell CF1 embryos developed into blastocysts, compared to 46 and 43% for ECM and mT6, respectively. Moreover, the cell numbers of blastocysts developing in TE (7.49 +/- 3.3) were higher than the cell numbers of those developing in ECM (55.1 +/- 2.4). The culture requirements of embryos varied between different stocks of mice: Fewer CF1 embryos developed to the blastocyst stage than either Dub:ICR embryos (90%) or CD-1 embryos (84%). Lowering the osmolarity of the medium from 300 to 280 mOSM, increasing the concentration of KC1 from 1.42 to 25 mM, or omitting lactate from the medium during Day 1 of culture did not further improve development of embryos, in contrast to previous reports. However, the time at which embryos were transferred to outgrowth medium influenced their postblastocyst development. The best development was observed when embryos were transferred on Day 4 of culture at the late morula-early blastocyst stage.