Fig. 2. Interactions between GDF9 and TGFß1 or oocyte-stimulated granulosa cell DNA synthesis. Mural GCs were cultured with increasing doses of mouse GDF9 either alone or in the presence of DOs (16 DOs/125-µl well) or human TGFß1 (0.5 ng/ml). After 24 hours of culture the labelled thymidine incorporated into cells was counted. Points are means ± s.e.m. from at least triplicate wells from five replicate experiments. The stimulatory effects of TGFß1 and oocytes were additive to the stimulatory actions of GDF9 at low doses of GDF9 [means with an asterisk are significantly different to GDF9 alone at that dose (2-way ANOVA; P<0.01)], whereas this additive effect was lost at higher doses of GDF9 (>8 ng/ml for DOs; >15 ng/ml for TGF-ß1; dose GDF9 X treatment interaction, P<0.001).