Figure 2: Insulin and IGF1 signal transduction is functional in osteoblast precursors in vitro. IR mRNA levels measured by quantitative RT-PCR in MC3T3-E1 cells after 1, 2, 3, or 4 weeks of differentiation with ascorbate and ß-glycerol phosphate (A) and in primary calvariae, C3H10T1/2, MC3T3-E1, and bone marrow stromal cell cultures (B). Western blot detection of Akt and ERK1/2 phosphorylation in C3H10T1/2 (C) or MC3T3-E1 (D) cell lysates prepared after treating cells with 10 ng/ml of insulin or IGF-1 for the indicated times.