Quantification of the transition from oocyte-coded to embryo-coded glucose phosphate isomerase in mouse embryos

A quantitative electrophoretic analysis of glucose phosphate isomerase (GPI-1) allozymes produced by heterozygous Gpi-1sa / Gpi-1sb mouse embryos has enabled us to estimate separately the contributions of GPI-1 enzyme that were (1) oocyte coded, (2) encoded by the embryonic, maternally derived Gpi-1sa allele and (3) encoded by the embryonic, paternally derived Gpi-1sb allele. The oocyte-coded GPI-1 activity is stable until 2½ days and then declines and is exhausted by 5½ to 6½ days post coitum (p.c) . The maternally and paternally derived Gpi-1s alleles are probably usually activated synchronously but several possible exceptions were observed. This activation was first detected in 2½-day embryos. Total GPI-1 activity falls to a minimum around 3½ to 4½ days, even though embryonic gene expression has already begun. The profile of oocyte-coded GPI-1 activity is consistent with the suggestion (Harper & Monk, 1983) hat there is a mechanism for the removal of oocyte-coded gene products at around 2½ days p.c. The method of analysis described is applicable to other dimeric enzymes with electrophoretic variants.