Systematic non-uniform distribution of parthenogenetic cells in adult mouse chimaeras.

Even though pure parthenogenetic mouse embryos die shortly after implantation, their cells are capable of participating in normal development of chimaeras when aggregated with fertilized embryos. Here we present data on parthenogenetic contribution to the oocyte populations measured by progeny tests in female chimaeras, and on distribution of parthenogenetic cells among the different organs by GPI typing. Systematic uneven distribution was detected. The highest level of participation was registered in the tissues of permanent cells (e.g. up to 63% in female germline). On the other hand, parthenogenetic cells were absent in several tissues that have extensive capacity for postnatal growth or selfrenewal. This finding suggests that uneven selective processes operate against parthenogenetic cells within certain differentiation pathways during fetal and postnatal life, as has already been observed in the development of extraembryonal membranes. It is likely that more than one mechanism is responsible for these selections. Parthenogenetic cells may start to differentiate in all cell lineages, but they are not able to react normally at certain points in the developmental pathway, for example to induction signals and, therefore, the cells fail to complete the normal processes of development, or to the proliferation requirement so that the fertilized counterpart gradually takes over the cell lineage. Paternally derived gene(s) might have a unique role in the development of tissues lacking parthenogenetic contribution.