The transition from oocyte-coded to embryo-coded glucose phosphate isomerase in the early mouse embryo

The proportions of glucose phosphate isomerase (GPI-1) allozymes produced by early (Gpi-1sa/Gpi-1sb female X Gpi-1sc/Gpi-1sc male)F1 mouse embryos were analysed by quantitative cellulose acetate electrophoresis. Technical controls showed that this system is extremely sensitive, quantitatively reproducible and quite accurate. Genetic controls established that the Gpi-1sa/Gpi-1sb mothers were homozygous for the Gpi-1tb temporal allele, that produces relatively high GPI-1 activity in the oocyte. The oocyte-coded enzyme lasted until about 5 1/2 days post coitum (p.c.) or shortly thereafter. The maternally derived, embryonic Gpi-1s allele was expressed no earlier than the paternally derived allele. This was first expressed between 2 1/2 and 3 1/2 days p.c. In this cross, most of the transition from oocyte-coded to embryo-coded GPI-1 occurred between 2 1/2 and 5 1/2 days p.c.