The microRNA-200 family mediates hair follicle development through coordinated regulation of cell adhesion and polarity

The microRNA-200 family is highly expressed in epithelial cells and frequently lost in metastatic cancer. Although the tumor-suppressing roles of this family are well documented and directly linked to the inhibition of mesenchymal genes, their targets and functions in normal epithelial tissues remain unclear. Furthermore, how the two sub-families of the five-microRNA family distinguished by a single nucleotide within the seed region regulate their targets is unclear. Here we show that the microRNA-200 family governs hair morphogenesis and fine-tunes stem cell specification by regulating cell adhesion, polarity and signaling pathways. By directly ligating microRNAs to their targeted mRNA regions, we identify numerous targets involved in the regulation of actin cytoskeleton, focal adhesion, cell cycle and Hippo/Yap signaling in a miRNA:mRNA pair-specific manner. The two sub-families bind to largely distinct target sites although many genes are regulated by both sub-families for a greater degree of regulation. Using inducible and knockout mouse models, we show that the microRNA-200 family enhances cell adhesion, inhibits migration and reduces cell division, contributing to precise stem cell specification. Our findings demonstrate that combinatorial targeting of many genes is critical for microRNA functions and provide new insights into microRNA-200s’ functions in normal epithelial tissues. Total RNA extracted from hair germ (HG) and interfollicular epidermis (IFE) from pTRE2-200bcl/K14rtTA (Tg) and control (ctrl) animals at P0.5.