Developmental molecular genetics of the mouse and its embryonal carcinoma

Saturation germ line mutagenesis of the murine t region including a lethal allele at the quaking locus

The proximal region of mouse chromosome 17 contains many genes affecting embryonic development, germ cell differentiation, and the immune system. Although the study of natural variation, including t haplotypes, has yielded some information about the function of these genes, spontaneous variants often exhibit manifold genetic effects and are generally not carried on inbred backgrounds. To clearly connect phenotypes with the actions of individual genes, mutants in which genes are altered singly are needed. Therefore, we used a highly efficient point mutagen, N-ethyl-N-nitrosourea, in combination with classical breeding schemes to induce and identify recessive lethal mutations in the t region. Of 350 mutagenized gametes examined, at least 10 independent recessive embryonic lethal mutations have been identified; an additional two are perinatal lethals. A spontaneous brachyury mutation, TWis, arose on a genetic background that permits high-resolution mapping of the induced recessive mutations against cloned DNA sequences from the t region. One lethal mutation is an allele at the quaking locus. The multiple alleles of quaking and the feasibility of high-resolution mapping permit investigation of the pleiotropic action of this locus in mammalian development.

Induction of recessive lethal mutations in the T/t-H-2 region of the mouse genome by a point mutagen

TheT/t–H-2region on mouse chromosome 17 is known from complex natural variants (‘t-haplotypes’) to contain numerous genes, including some affecting the immune system and the development of the embryo. Rapid progress in the isolation of recombinant DNA clones for this 50 megabasepair region is generating the material for its complete molecular anatomy. A crucial step in revealing the biological functions controlled by the region is to obtain mutants in which genes are inactivated individually. We have used a pair of inbred mouse strains and a series of classical breeding schemes that permit the detection of recessive lethal and detrimental mutations in theT/t–H-2region.

In this initial phase of our study, 280 gametes mutagenized in the male germ line by ethylnitrosourea (ENU) have yielded eleven independent pre-natal recessive lethal mutations. Four have been mapped againstTmutations and have been shown to complement one another in all pairwise combinations.