MiRNA-let-7b decreases proliferation activities and development of follicular cells via targeting MAP3K1 gene

To date, it has not yet been determined if the apoptosis of follicular granulosa cells (FGCs) is mediated by miR- let-7b via MAP3K1. In the present study, FGCs were transfected with a miR-let-7b mimic at different doses (0, 40, 60, 80, 100 and 120 μM), and were allocated into the control group (CG), and MIM-1, MIM-2, MIM-3, MIM-4 and MIM-5, respectively. Expression levels of miR-let-7b and mitogen-activated protein kinase kinase kinase 1 (MAP3K1) mRNAs and proteins were determined using RT-PCR and Western blots. Luciferase report assay was applied to verify the targeting relationship between miR-let-7b and MAP3K1. The results revealed that the proliferation activity of FGCs in the MIM-4 group was significantly lower than that of the CG and MIM-1 groups (P<0.05). The MiR-let-7b mimic obviously reduced expression levels of miR-let-7b of the FGCs. The largest reduction was found in MIM-4. Levels of MAP3K1 mRNAs and proteins in the MIM-3 and MIM-4 groups were lower than that of the CG (P<0.05 or P<0.01). Co-transfection of let-7b mimic significantly inhibited luciferase activity (P<0.05) as compared with the CG. In conclusion, miR-let-7b may obviously depress the cell viability and accelerate apoptosis of ovine FGCs. Higher doses of miR-let-7b mimic (80 μM and 100 μM) could significantly depress expressions of miR-let-7b mRNAs, MAP3K1 mRNAs and protein in ovine FGCs. MiR-let-7b promoted FGCs apoptosis by inhibiting the MAP3K1 gene.