Efficient generation of selection-gene-free rat knockout models by homologous recombination in ES cells

Embryonic stem cell (ES cell)-based rat knockout technology, although successfully developed in 2010, has seen very limited usage to date due to low targeting efficiency and a lack of optimized procedures. In this study, we performed gene targeting in ES cells from the Sprague-Dawley (SD) and the Fischer 344 (F344) rat strains using an optimized procedure and the self-excising neomycin (neo)-positive selection cassette ACN to successfully generate Leptin and Trp53 knockout rats that did not carry the selection gene. These results demonstrate that our simplified targeting strategy using ACN provides an efficient approach to knock out many other rat genes.