STRAIN-SPECIFIC DIFFERENCES IN MOUSE OOCYTES AND THEIR CONTRIBUTIONS TO EPIGENETIC INHERITANCE

Previous experiments revealed a strain-dependent effect of egg cytopla sm on the developmental potential of androgenetic (two paternal genome s) mouse embryos, Eggs obtained from C57BL/6 mice supported androgenon e development to the blastocyst stage at a much higher frequency than eggs from DBA/2 mice. Transient exposure of paternal pronuclei to DBA/ 2 egg cytoplasm also compromised development, indicating that the DBA/ 2 egg cytoplasm negatively affected the ability of paternal pronuclei to support blastocyst formation, An essential first step toward unders tanding the molecular mechanism by which egg modifier factors influenc e gene expression is to determine the number of loci that are responsi ble for the strain difference. To do this, (B6D2)F-1 hybrid females we re backcrossed to DBA/2 males and the eggs from individual female prog eny assayed for their ability to support androgenetic development. App roximately one fourth of the backcross females produced eggs that fail ed to support androgenone development, indicating that two independent ly segregating genetic loci are most likely responsible for the differ ence between DBA/2 and C57BL/6 egg phenotypes, Comparison of DBA/2 and C57BL/6 oocytes by two-dimensional protein gel electrophoresis reveal ed at least 17 proteins that exhibited significant, reproducible, quan titative differences in rates of synthesis, All of these proteins were synthesized in (B6D2)F-1 oocytes, These data, combined with the previ ous observation that the C57BL/6 egg phenotype is dominant, are consis tent with a model in which a C57BL/6 allele at either locus provides a protective function, either by antagonizing the actions of the DBA/2 alleles or by providing, through partial or complete redundancy, a fun ction not provided by the DBA/2 alleles.