The effect of short-term labelling in (3H) thymidine on the viability of mouse blastomeres: alone and in combination with unlabelled blastomeres.

A method of labelling 8-cell-stage mouse blastomeres with [3H]thymidine is described, which allows them to be followed to the late blastocyst stage and is compatible with normal postimplantation development. However, the [3H]thymidine does affect the postimplantation vigour of the cells when placed in competition with unlabelled cells in blastomere aggregates. This suggests that caution should be used in interpreting results using [3H]thymidine as a label for early mammalian cells.