Glucosephosphate I somerase Distribution During Oocyte Maturation and Early Embryologic Stages of the Mouse1

The enzyme glucosephosphate isomerase (GPI) is of interest because of its role in glycolysis and its use as a cell marker in studies of embryogenesis utilizing chimeras. The distribution of GPI was determined in histologic sections of ovarian follicles and the tissues of early embryonic stages of the mouse. Antibodies of GPI were combined in an immunocytochemical procedure utilizing peroxidase-antiperoxidase to localize GPI in tissue sections.During follicular maturation, GPI is first detected in oocytes of small follicles and then in the granulosa cells of slightly larger follicles. The relative concentrations of GPI remain high in the granulosa cells adjacent to the oocyte as the follicles mature. GPI in the granulosa cells may play a role in providing the growing oocyte with low molecular weight energy sources. Within the conceptus, differences in GPI concentrations among tissues become apparent during the formation of the egg cylinder. The highest concentrations of GPI are in the embryonic ectoderm, the amniotic folds, the extraembryonic ectoderm, and the ectoplacental cone. These are areas of intense mitotic activity. The energy required for cell divisions during embryogenesis is derived from glycolysis, thus the high concentrations of GPI in these tissues correlates well with the cellular function.