HPRT-deficient (Lesch–Nyhan) mouse embryos derived from germline colonization by cultured cells

Embryonal stem (ES) cell lines, established in culture from peri-implantation mouse blastocysts1–3, can colonize both the somatic and germ-cell lineages of chimaeric mice following injection into host blastocysts4,5. Recently, ES cells with multiple integrations of retro viral sequences have been used to introduce these sequences into the germ-line of chimaeric mice5, demonstrating an alternative to the microinjection of fertilized eggs6for the production of transgenic mice. However, the properties of ES cells raise a unique possibility: that of using the techniques of somatic cell genetics to select cells with genetic modifications such as recessive mutations, and of introducing these mutations into the mouse germ line. Here we report the realization of this possibility by the selection in vitro of variant ES cells deficient in hypoxanthine guanine phosphoribosyl transferase (HPRT; EC 2.4.2.8), their use to produce germline chimaeras resulting in female offspring heterozygous for HPRT-deficiency, and the generation of HPRT-deficient preimplantation embryos from these females. In human males, HPRT deficiency causes Lesch–Nyhan syndrome7, which is characterized by mental retardation and self-mutilation.