The chicken HPRT gene: a counter selectable marker for the DT40 cell line

We describe the cloning, characterisation and chromosomal mapping of the ch icken hprt gene together with the construction of two counter selectable hp rt(-/-) DT40 derived cell lines; One of these cell lines contains a stably integrated gene encoding a conditionally active cre recombinase and thus al lows efficient manipulation of targeted loci by site-specific recombination . These cell lines will enhance the utility of the hyper-recombinogenic DT4 0 cell line as a system for the genetic analysis of cell autonomous functio ns in vertebrates and as a tool for mammalian chromosome engineering.