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Renée Emily Hilker, Bo Pan, Xiaoshu Zhan, and Julang Li

In antral follicles, the transition of proliferative granulosa cells to estradiol-producing is critical for proper oocyte maturation. MicroRNAs are noncoding RNAs that play important roles in ovarian follicular development; however, this has yet to be fully characterized. MicroRNA-21 is significantly higher in granulosa cells isolated from large antral follicles compared to those from small antral follicles. To investigate the function of miR-21, porcine granulosa cells were transfected with miR-21 mimic or miR-21 targeted siRNA. Cells with the miR-21 mimic had higher aromatase expression and estradiol production but decreased WT1 expression. Conversely, cells with the miR-21 siRNA secreted less estradiol and had higher WT1 expression. We hypothesized that miR-21 promotes estradiol production by inhibiting WT1 protein synthesis. We found a potential miR-21 binding site in the 3’UTR of the WT1 transcript and performed a dual-luciferase reporter assay using the WT and mutated 3’UTR. Compared to the negative control, the miR-21 mimic induced a significant decrease in luciferase activity in the WT 3’UTR. This decrease was reversed when the 3’UTR was mutated, suggesting miR-21 targets this site to inhibit WT1 expression. We next transfected porcine granulosa cells with WT1 targeted siRNA and observed a significant increase in aromatase expression and estradiol secretion. We propose that miR-21 represses WT1 expression in granulosa cells to potentially promote aromatase expression and estradiol production. This study offers the first report of a microRNA regulating WT1 expression in granulosa cells and reveals the role of miR-21 in WT1’s regulation of estradiol production.

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Hui Juan Zhu, Hui Pan, Xu Zhe Zhang, Nai Shi Li, Lin Jie Wang, Hong Bo Yang, and Feng Ying Gong

Myostatin is a critical negative regulator of skeletal muscle development, and has been reported to be involved in the progression of obesity and diabetes. In the present study, we explored the effects of myostatin on the proliferation and differentiation of 3T3-L1 preadipocytes by using 3-[4,5-dimethylthiazol-2-yl] 2,5-diphenyl tetrazolium bromide spectrophotometry, intracellular triglyceride (TG) assays, and real-time quantitative RT-PCR methods. The results indicated that recombinant myostatin significantly promoted the proliferation of 3T3-L1 preadipocytes and the expression of proliferation-related genes, including Cyclin B2, Cyclin D 1, Cyclin E1, Pcna, and c-Myc, and IGF1 levels in the medium of 3T3-L1 were notably upregulated by 35.2, 30.5, 20.5, 33.4, 51.2, and 179% respectively (all P<0.01) in myostatin-treated 3T3-L1 cells. Meanwhile, the intracellular lipid content of myostatin-treated cells was notably reduced as compared with the non-treated cells. Additionally, the mRNA levels of Ppar γ, Cebp α, Gpdh, Dgat, Acs1, Atgl, and Hsl were significantly downregulated by 22–76% in fully differentiated myostatin-treated adipocytes. Finally, myostatin regulated the mRNA levels and secretion of adipokines, including Adiponectin, Resistin, Visfatin, and plasminogen activator inhibitor-1 (PAI-1) in 3T3-L1 adipocytes (all P<0.001). Above all, myostatin promoted 3T3-L1 proliferation by increasing the expression of cell-proliferation-related genes and by stimulating IGF1 secretion. Myostatin inhibited 3T3-L1 adipocyte differentiation by suppressing Ppar γ and Cebp α expression, which consequently deceased lipid accumulation in 3T3-L1 cells by inhibiting the expression of critical lipogenic enzymes and by promoting the expression of lipolytic enzymes. Finally, myostatin modulated the expression and secretion of adipokines in fully differentiated 3T3-L1 adipocytes.