PROGRAMMED MOUSE GENOME MODIFICATIONS

The availability, in the mouse, of embryonic stem cells (ES cells) whi ch have the ability to colonize the germ line of a developing embryo, has opened entirely new avenues to the genetic approach of embryonic d evelopment, physiology and pathology of this animal. Indeed, it is now possible, using homologous recombination in ES cells, to introduce mu tations in any gene as long as it has been cloned. Thus, null as well as more subtle mutations can be created. Furthermore, scenarios are cu rrently being derived which will allow one to generate conditional mut ations. Taken together, these methods offer a tremendous tool to study gene function in vivo, they also open the way to creating murine mode ls of human genetic diseases.