Widespread recombinase expression using FLPeR (flipper) mice

As conditional genetic strategies advance, the need for multiple site-speci fic recombinase systems has emerged. To meet this need in part, we have tar geted the constitutive ROSA26 locus to create a mouse strain with generaliz ed expression of the enhanced version of the site-specific recombinase FLP (FLPe), This strain is designated FLPeR ("flipper"), Using this strain, ext ensive target gene recombination can be achieved in most tissue types, incl uding cells of the developing germ line. FLPeR mice therefore serve two imp ortant functions: as a source of many different FLPe-expressing primary cel l lines and as a deleter strain, Moreover, because the FLPeR mouse is a 129 -derived strain, a 129 genetic background can be preserved when crossed to most ES cell-derived mice, This enables conditional genetic alterations to be maintained on a standard background, a feature important for obtaining r eproducible results and genetically defined controls. (C) 2000 Wiley-Liss, Inc.