Establishment and Chimera Analysis o f 129/SvEv- and C57BL/6 - Derived Mouse Embr y - onic Stem Cell Line s

ABSTRACT Hundreds of new mutant mouse lines arebeing produced annually using gene target-ing and gene trap approaches in embryonicstem (ES) cells, and the number is expectedegenome projects progress. The availabilityof robust ES cell lines and a simple techno-logy for making chimeras is more attractivenow than ever before. We established severalnew ES cell lines from 129/SvEv andC57BL/6 mice and tested their ability tocontribute to the germline following blast-ocyst injections and/or the less expensive andeasier method of morula-ES cell aggreg- ation. Using morula aggregation to producechimeras, five newly derived 129/SvEv andtwo C57BL/6 ES cell lines tested at earlypassages were found to contribute extensive -ly to chimeras and produce germline-tran-smitting male chimeras. Furthermore, thetwo 129S/vEv ES cell lines that were testedand one of the C57BL/6 ES cell lines wereable to maintain these characteristics aftermany passages in vitro. Our results indicatethat the ability of ES cells to contributestrongly to chimeras following aggregationwith outbred embryos is a general propertyof early passage ES cells and can be mai-ntained for many passages. C56BL/6-derivedES cell lines, however, have a greater te- ndency than 129-derived ES cell lines to losetheir ability to colonize the germline.