29 Systematic elimination of parthenogenetic cells in mouse chimeras

The developmental potential of primitive ectoderm cells lacking paternal chromosomes was investigated by examining the distribution of parthenogenetic cells in chimeras. Using GPI-1 allozymes as marker, partheno-genetic cells were detected in most organs and tissues in adult chimeras. However, these cells were under severe selective pressure compared with cells from normal fertilized embryos. In the majority of chimeras, par-thenogenetic cells in individual animals were observed in a limited number of tissues and organs and, even in these instances, their contribution was substantially reduced. Nevertheless, parthenogenetic cells were detected more consistently in some organs, especially the brain, heart, kidney and spleen. In contrast, there was apparently a systematic selection against parthenogenetic cells in some tissues, most notably in skeletal muscle, liver and pancreas. These results suggest that paternally derived genes are probably required not only for the develop-ment of extraembryonic structures but also for sub-sequent development of embryonic tissues derived from the primitive ectoderm lineage