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.