TRANSGENIC MICE FOR THE ESTABLISHMENT OF HISTIDINOL-RESISTANT EMBRYONIC FIBROBLAST FEEDER LAYERS

Gene targeting in mouse embryonic stem cells generates mutations by re placing an endogenous chromosomal region with a copy disrupted by a se lectable genetic marker, The most commonly used selectable marker is t he bacterial neo(r) gene, which confers resistance in mammalian cells to the antibiotic G418. Use of an alternative selectable marker, the S almonella typhimurium gene hisD, should provide expanded applications for gene targeting, The hisD gene encodes the protein histidinol dehyd rogenase, which catalyzes the conversion of histidinol to the amino ac id histidine. Histidinol is toxic to mammalian cells, while histidine is an essential mammalian amino acid, Consequently, growth selection i n cultures with media containing histidinol in place of histidine occu rs by both histidine starvation and histidinol poisoning, The hisD sel ection is being tested for potential use in gene targeting experiments with mouse embryonic stem (ES) cells, Currently, most successful gene targeting experiments use primary embryonic fibroblast feeder layers, which assist in the maintenance of the pluripotential state of the em bryonic stem cells, To support ES cell stability under histidinol sele ction, mice transgenic for the S, typhimurium hisD gene have been prod uced and used to generate embryonic fibroblast feeder cells, The trans genic embryonic fibroblasts survive under a wide range of histidinol-c ontaining growth conditions and support growth of ES cell cultures.