Mapping of the two mouse engrailed-like genes: close linkage of En-1 to dominant hemimelia (Dh) on chromosome 1 and of En-2 to hemimelic extra-toes (Hx) on chromosome 5.

The mouse genome contains two genes, En-1 and En-2, with sequence similarity to the engrailed gene of Drosophila. Using conventional linkage crosses, we have shown that En-1 maps approximately 0.28 cM distal to the dominant hemimelia (Dh) gene on chromosome 1 and that En-2 maps approximately 1.1 cM proximal to the hemimelic extra-toes (Hx) gene on chromosome 5. We have also shown by Northern blot analysis that En-1 transcripts in Dh homozygotes and En-2 transcripts in Hx homozygotes are of normal size and abundance. These data, in conjunction with previously published studies of the patterns of En-1 and En-2 expression in developing mouse embryos, suggest that Dh and Hx are very unlikely to be mutant alleles of En-1 or En-2, respectively. Instead, we suggest that En-1-Dh and En-2-Hx represent paralogous linkage groups that evolved following duplication of a common ancestral chromosome segment.