New technology for an old favorite: lentiviral transgenesis and RNAi in rats.

The ability to produce targeted deletions in the mouse genome via homologous recombination has been a hallmark of mouse genetics, and has lead to the production of thousands of gene knockouts. New technologies are making it possible to disrupt gene function in many other species. This article reviews some of these methods, highlighting the powerful combination of lentiviral vectors with RNA interference (RNAi), which allows one to produce transgenic animals expressing short hairpin RNA (shRNA) to "knock down" specific gene expression. Lentiviral transduction of embryos has been shown to be a highly efficient means of transgenesis, and is particularly promising for animals that are considered difficult to genetically modify by DNA pronuclear injection. This technique has been popular for introducing transgenes for shRNA expression into rodents and its utility for creating new genetic models has already been demonstrated. One of the purported advantages of in vivo RNAi is that shRNA expressing transgenes would be expected to act in a dominant nature, resulting in a phenotype in founder animals. However, one possible concern with lentiviral-mediated transgenesis is the potential for mosaicism in founders, and the data for this phenomenon and the potential causes and solutions are discussed. Emphasis is placed on the application of in vivo RNAi, and other reverse genetic methods, for creating new genetic models in the rat.