ESR1 and polycystic ovary syndrome: Let-7 has been shown to regulate the TGF-β signaling pathway by targeting the activin receptor I and Smad2/3 genes [47], contributing to reproductive abnormalities in PCOS such as the perturbation of follicle development and hyperandrogenism [48], whereas miR-140, a tumor suppressor miRNA whose downregulation has been proved to be mediated via ERα signaling [49], has been altered in PCOS.