Effects of Species Differences on Oocyte Regulation of Granulosa Cell Proliferation

The role of oocytes in regulating ovulation quota between species is not fully understood. In humans, sheep, and rodents the oocyte-derived growth factors, bone morphogenetic protein 15 (BMP15) and/or growth differentiation factor 9 (GDF9) have profound effects on ovarian follicular development and ovulation quota. The aim of these studies was to compare the ability of oocytes from sheep (low ovulation-rate) and rat (poly-ovulator) to stimulate radiolabelled ³H-thymidine uptake by granulosa cells (GC) both within and between the two species, and to assess species differences of GDF9 and BMP15 in co-incubations. For these experiments, oocytes denuded of cumulus-cells (DO) were co-incubated with a fixed number of GC from either species. Rat or sheep DO stimulated ³H-thymidine uptake by GC from the same species (P<0.005). Sheep oocytes also stimulated ³H-thymidine uptake by rat GC (P<0.001) but not vice versa. To investigate this further, oocytes and GC were co-incubated with monoclonal antibodies specific to GDF9 or BMP15 or to a hydatids antigen (control). Both sheep and rat oocyte stimulation of ³H-thymidine uptake by GC was inhibited with the GDF9 antibody (P<0.05) but not the control antibody, irrespective of the species of GC. Sheep DO stimulation of rat GC was also inhibited using an antibody to BMP15 (P