Evolution of Duplicated Hox Gene Clusters in Land Snails and Slugs.

Terrestrial slugs and snails, order Stylommatophora, underwent a genome duplication in their ancestry. This affords an opportunity to examine how Hox gene clusters evolved after duplication in an invertebrate group and compare to the well-studied genome duplications of vertebrates. Using genomic data and PCR verification, we describe Hox gene organization for 10 species of Stylommatophora and one close relative. All Stylommatophora sampled have two broken Hox gene clusters. The HoxA cluster is dispersed along one chromosome and generally has 9 genes, but only 8 genes in slugs. The HoxB cluster is dispersed along a different chromosome and usually has 7 genes, but only 6 genes in giant African land snails. No cluster has a full complement of 11 genes. The patchwork retention of duplicated Hox genes shows striking similarities to duplicated vertebrate Hox gene clusters.