Rapid functional dissection of genetic networks via tissue-specific transduction and RNAi in mouse embryos

Using the skin epidermis as a model for studies of epithelial biology and tumorigenesis and lentiviruses carrying RNAi or Cre recombinase, Beronja and colleagues describe a noninvasive, in vivo method for cell type–specific loss-of-function studies in the surface epithelia of mouse embryos. This approach can be used for the rapid functional assay of genes, the dissection of genetic interactions within complex regulatory pathways, and the study of the role of putative tumor suppressors and oncogenes in regulating growth control. Using ultrasound-guided in utero infections of fluorescently traceable lentiviruses carrying RNAi or Cre recombinase into mouse embryos, we have demonstrated noninvasive, highly efficient selective transduction of surface epithelium, in which progenitors stably incorporate and propagate the desired genetic alterations. We achieved epidermal-specific infection using small generic promoters of existing lentiviral short hairpin RNA libraries, thus enabling rapid assessment of gene function as well as complex genetic interactions in skin morphogenesis and disease in vivo. We adapted this technology to devise a new quantitative method for ascertaining whether a gene confers a growth advantage or disadvantage in skin tumorigenesis. Using α1-catenin as a model, we uncover new insights into its role as a widely expressed tumor suppressor and reveal physiological interactions between Ctnna1 and the Hras1-Mapk3 and Trp53 gene pathways in regulating skin cell proliferation and apoptosis. Our study illustrates the strategy and its broad applicability for investigations of tissue morphogenesis, lineage specification and cancers.