Effect of blastomere sex and fluorescent labelling on the development of bovine chimeric embryos reconstituted at the four-cell stage

The development rate of bovine chimeric embryos reconstituted at the 4‐cell stage is relatively low. If chimerism is to be used as an approach in producing transgenic livestock, it is important to investigate whether this rate is affected by the sex of the blastomeres being combined and if all blastomeres survive equally well. In Experiment 1, blastomeres from 4‐cell stage embryos were inserted into surrogate zonae pellucidae either in pairs to reconstitute 4‐cell chimeras, or as the original sets of four to make handled controls. The development of chimeras with one pair of blastomeres labelled with PKH26‐GL was also investigated. The rate of development into blastocysts was similar in chimeras with unlabelled blastomeres (23%) and in those in which one pair of blastomeres was labelled (26%) and was lower (P 0.05). These results suggest that, in addition to the negative effects of micromanipulation, factors other than the sex of the blastomeres are involved in the reduced rate of development of chimeric bovine embryos. They also confirm the usefulness of PKH26‐GL labelling for tracking the progeny of cleaving bovine blastomeres at least to the blastocyst stage. Mol. Reprod. Dev. 60: 202–207, 2001. © 2001 Wiley‐Liss, Inc.