1. ^*Department of Pathology, University of Edinburgh, Teviot Place, Edinburgh EH8 9AG, UK
2. ^†MRC Experimental Embryology and Teratology Unit, Woodmansterne Road, Carshalton, Surrey SM5 4EF, UK
3. ^‡MRC Mammalian Development Unit, Wolfson House, 4 Stephenson Way, London NW1 2HE, UK
4. ^§Present address: Institute of Obstetrics and Gynaecology, Hammersmith Hospital, Du Cane Road, London W12 0HS, UK.

Abstract

Embryonal stem (ES) cell lines, established in culture from peri-implantation mouse blastocysts^1–3, can colonize both the somatic and germ-cell lineages of chimaeric mice following injection into host blastocysts^4,5. 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 eggs⁶ for 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.