EMBRYONIC STEM-CELL LINES FROM MRL MICE ALLOW GENETIC-MODIFICATION INA MURINE MODEL OF AUTOIMMUNE-DISEASE

The MRL/MpJ-Fas(lpr) (MRL-lpr/lpr) mouse spontaneously develops a gene ralized autoimmune disease with features similar to those of systemic lupus erythematosus. This mouse strain provides a valuable system for identifying and characterizing the multiple genetic factors that influ ence the pathogenesis of autoimmune diseases. One of the most powerful means of examining the role of a specific gene product in vivo is by inactivating the gene in mouse embryonic stem (ES) cells by homologous recombination and using these cells to derive mouse lines carrying th e inactivated gene. The successful applications of this approach, howe ver, requires an ES cell line that will remain stable in culture durin g the processes of genetic manipulation and selection. The date, ES ce ll lines that meet this criterion have been derived from only a few mo use strains. Here we describe the production and characterization of s table ES cell lines from the MRL mouse strain. Approximately 75 of the blastocysts derived from the MRL/MpJ + (MRL-+/-) strain gave rise to ES cell lines, and both of the male MRL-+/- ES cell lines tested were shown to be germline competent. We show that the MRL-+/- ES cell lines undergo gene targeting by homologous recombination at high frequency by inactivating the gene encoding the EP2 prostaglandin receptor. Thes e Ep2-targeted MRL ES cell lines were used to generate MRL mouse lines heterozygous for the disrupted Ep2 gene, thus demonstrating the feasi bility of using a genetic approach to dissect the pathobiology of the autoimmune disease in the MRL mouse.