Influence of parental chromosomes on spatial specificity in androgenetic ↔ parthenogenetic chimaeras in the mouse

The presence of both parental genomes is essential for development to term in the mouse embryo1–5 probably because of germline-specific modifications of homologous chromosomes6,7. Neither androgenetic nor parthenogenetic embryos can by themselves develop to term; any post-implantation embryos they produce have opposite phenotypes, which reflects the presence of complementary information in parental chromosomes1,7,8. The development of androgenetic ↔ parthenogenetic chimaeras is of considerable interest because in this case both parental chromosomes are available even though they are in separate cells. We demonstrate here that in post-implantation chimaeric fetuses, the expression of parental information results in spatial specificity so that parthenogenetic cells are confined to the embryo but the trophoblast consists almost entirely of androgenetic cells. The yolk sac contains both cell types. However, there is incomplete functional complementation because the chimaeras do not reach term. Although failure to reach term may occur partly because of inadequate intermingling and interactions between embryonic cells, it is more likely that further control of mouse development depends on the presence of both sets of chromosomes within the same cells.