Effect of IGF-I on ERK1/2 phosphorylation in cultured zebrafish follicle cells. A, Time course of IGF-I activation of ERK1/2 in the follicle cells (upper) and blockade of IGF-I effect on ERK1/2 by specific MEK inhibitors, PD98059 and U0126 (lower). Cultured zebrafish follicle cells were pretreated with PD98059 (25 μM) or U0126 (10 μM) for 30 minutes before treatment with IGF-I (50 ng/mL) for 15 minutes. p-ERK1/2, phosphorylated ERK1/2; t-ERK1/2, total ERK1/2. B–E, Dose response of GW5074, PD98059, U0126, and FR180204 effects on the basal expression of kitlga in cultured zebrafish follicle cells after 6 hours of treatment. F–I, Effects of IGF-I on the expression of kitlga in the presence of GW5074 (1 μM), PD98059 (25 μM), U0126 (10 μM), and FR180204 (25 μM) in cultured zebrafish follicle cells. The cells were pretreated with the drugs for 30 minutes before treatment with IGF-I (50 ng/mL) for 6 hours. The data were normalized to the housekeeping gene ef1a and expressed as the percentage of the control group (mean ± SEM; n = 4). Statistical significance was indicated by asterisk (*, P < .05; **, P < .01; ***, P < .001) or different letters (P < .05).