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Similar Effects of Osmolarity, Glucose, and Phosphate on Cleavage past the 2-Cell Stage in Mouse Embryos from Outbred and F₁ Hybrid Females¹

Hormones, Growth and Development Program,³ Ottawa Health Research Institute, Department of Obstetrics and Gynecology (Division of Reproductive Medicine),⁴ Department of Cellular and Molecular Medicine,⁵ Department of Biology,⁶ University of Ottawa, Ottawa, Ontario, Canada K1Y 4E9

One-cell-stage embryos derived from most random-bred and inbred female mice exhibit an in vitro developmental block at the two-cell stage in classical embryo culture media. However, embryos derived from many F₁ hybrids develop easily past the two-cell stage under the same conditions. This has given rise to the commonly accepted idea that there exist blocking and nonblocking types of female mice, with only the former being prone to a two-cell block. Recently, culture media have been improved to the point that even embryos prone to the two-cell block will develop past the block in vitro, making it possible to study its etiology. Here, we show that either increased osmolarity or increased glucose/phosphate levels induced the expected two-cell block in random-bred CF1 embryos and the two-cell block at increased osmolarities could be rescued by the organic osmolyte glycine. Surprisingly, one-cell embryos from B6D2F₁ (BDF₁) F₁ hybrid females, considered to be nonblocking, also became blocked at the two-cell stage when osmolarity or glucose/phosphate levels were increased. They were also similarly rescued by glycine from the osmolarity-induced block. The most evident difference was that the purportedly nonblocking embryos became blocked at a higher threshold of osmolarity or glucose/phosphate level than those considered prone to this developmental block. Thus, both blocking and nonblocking embryos actually exhibit a similar two-cell block to development.

¹ Supported by Canadian Institutes of Health Research grant MOP12040 T.H. and M-A.H. contributed equally to this work.

² Correspondence: Jay M. Baltz, Moses and Rose Loeb Research Centre, Ottawa Health Research Institute, 725 Parkdale Ave., Ottawa, ON K1Y 4E9, Canada. FAX: 613 761 5327; jbaltz{at}ohri.ca