Genetic analysis of the exed region in mouse

The extraembryonic ectoderm development (exed) mutant phenotype was describ ed in mice homozygous for the c(6H) deletion, a radiation-induced deletion in the tyrosinase region of mouse Chromosome 7. These mutants fail to gastr ulate and die around embryonic day 8.0. Several genes including, for exampl e, embryonic ectoderm development (eed), are deleted in the c(6H) mutants; however, the portion of the chromosome responsible for the more severe exed phenotype is localized:to a 20-kb region called the "exed-critical region. " To understand the genetics behind the exed phenotype, we analyzed this re gion in two ways. First, to determine whether the 20-kb exed-critical regio n alone causes the mutant phenotype, we removed it from a wild-type chromos ome. The resulting mice homozygous for this deletion were viable and fertil e, indicating that the 20-kb exed-critical region by itself is not sufficie nt to cause the phenotype when deleted. We then sequenced the 20-kb exed-cr itical region and no expressed exons were found. Several short matches to G enBank Expressed Sequence Tag (EST) databases were identified; however, non e of these ESTs mapped to the region, Taken together, these results indicat e that the exed phenotype may either be a position effect on a distal gene caused by the c(6H) breakpoint or the result of composite effects of nulliz ygosity of multiple genes in the deletion homozygotes. genesis 27:174-179, 2000. (C) 2000 Wiley-Liss, Inc.