Embryology
Similar effects of osmolarity, glucose, and phosphate on cleavage past the 2-Cell stage in mouse embryos from outbred and F1 hybrid females
By Nikhil, Journals Correspondent
Jan 4, 2005, 18:58

For many years it has been a puzzle why embryos from most random-bred and inbred female mice exhibit a block at the 2-cell stage in classical embryo culture media. Because embryos of many F1 hybrids develop beyond this stage, it has been thought that the phenotype is dependent on the genotype of the female giving rise to the egg - there are "blocking" and "non-blocking" types of females.

In the January 2005 issue of Biology of Reproduction, Hadi, Hammer, Algire, Richards, and Baltz revisit this issue. The recent development of media in which even blocking embryos develop to the blastocyst stage allowed them to address specific properties implicated in the 2-cell block and to test the hypothesis that the 2-cell block is not restricted to particular genotypes, but that instead there is varying susceptibility. They show that both blocked and non-blocked embryos are indeed susceptible to culture effects, with differences in the threshold of susceptibility. Increase in osmolarity or glucose/phosphate levels can cause 2-cell arrest of both blocking and non-blocking embryos, and the blocking effect of osmolarity is rescued by glycine. These results not only clear up long-standing confusion about the etiology of the 2-cell block but also highlight the important effects of culture conditions on experimental design.

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