Interdigitated deletion complexes on mouse chromosome 5 induced by irradiation of embryonic stem cells

Chromosome deletions have several applications in the genetic analysis of c omplex organisms. They can be used as reagents in region-directed mutagenes is, for mapping of simple or complex traits, or to identify biological cons equences of segmental haploidy, the latter being relevant to human contiguo us gene syndromes and imprinting. We have generated three deletion complexe s in ES (Embryonic Stem) cells that collectively span similar to 40 cM of p roximal mouse chromosome 5. The deletion complexes were produced by irradia tion of F-1 hybrid ES cells containing herpes simplex virus thymidine kinas e genes (tk) integrated at the Dpp6, Hdh (Huntington disease locus), or Gab rb1 loci, followed by selection for tk-deficient clones. Deletions centered at the adjacent Hdh and Dpp6 loci ranged up to similar to 20 cM or more in length and overlapped in an interdigitated fashion. However, the interval between Hdh and Gabrbl appeared to contain a locus haploinsufficient for ES cell viability, thereby preventing deletions of either complex from overla pping. In some cases, the deletions resolved the order of markers that were previously genetically inseparable. A subset of the ES cell-bearing deleti ons was injected into blastocysts to generate germline chimeras and establi sh lines of mice segregating the deletion chromosomes. At least 11 of the 2 6 lines injected were capable of producing germline chimeras. In general, t hose that failed to undergo germline transmission bore deletions larger tha n the germline-competent clones, suggesting that certain regions of chromos ome 5 contain haploinsufficient developmental genes, and/or that overall em bryonic viability is cumulatively decreased as more genes are rendered hemi zygous. Mice bearing deletions presumably spanning the semidominant hammert oe locus (Hm] had no phenotype, suggesting that the classic allele is a dom inant, gain-of-function mutation. Overlapping deletion complexes generated in the fashion described in this report will be useful as multipurpose gene tic tools and in systematic functional mapping of the mouse genome.