A, Proximal promoter sequences are important for basal activity of the mouse FSHβ promoter. Truncations of the mouse FSHβ promoter linked to luciferase were transiently transfected into LβT2, αT3-1, and NIH3T3 cells. Results represent the mean ± sem of at least three independent experiments, each performed in triplicate (n ≥ 9). Asterisks (*) designate a statistically significant difference from αT3-1 and NIH3T3 cells (P < 0.05) # designates significant difference from NIH3T3 cells (P < 0.05) but not αT3-1 cells; the letter a designates a statistical difference between the −64-bp FSHβLuc truncation and all other truncations in LβT2 cells (P < 0.05). Statistical differences between αT3-1 and NIH3T3 cells are not shown. B, Follistatin responsiveness of the mouse FSHβ promoter is localized to a more distal region of the promoter. LβT2 cells were transiently transfected with mouse FSHβLuc truncations and treated with either vehicle (control) or 100 ng/ml follistatin for 24 h (FS-treated, hatched bars). To facilitate comparisons between promoter responses, the control samples were set at 1 and the FS-treated samples are shown relative to this control. Results represent the mean ± sem of at least three independent experiments, each performed in triplicate (n ≥ 9). Bars marked with φ are statistically different from the untreated controls (P < 0.05).