LIN28A and LIN28B are conserved, developmentally regulated RNA binding proteins that inhibit the processing and maturation of the let-7 family of miRNAs. The let-7 miRNAs have been implicated in repression of oncogenes such as Ras, Myc, and HMGA2. It has recently been shown that upregulation of LIN28A and LIN28B in primary human tumors and human cancer cell lines is correlated with downregulation of let-7 miRNAs. LIN28 genes are reported to be involved in primordial germ cell development and germ cell malignancy. In addition, allelic variation in LIN28B is associated with regulating the timing of puberty in humans. Overexpression of LIN28A, in conjunction with Oct-4, Sox2, and Nanog, can reprogram human fibroblasts to pluripotent, ES-like cells.