Abstract
BackgroundDlx (Distal-less) genes have various developmental roles and are widespread throughout the animal kingdom, usually occurring as single copy genes in non-chordates and as multiple copies in most chordate genomes. While the genomic arrangement and function of these genes is well known in vertebrates and arthropods, information about Dlx genes in other organisms is scarce. We investigate the presence of Dlx genes in several annelid species and examine Dlx gene expression in the polychaete Pomatoceros lamarckii.ResultsTwo Dlx genes are present in P. lamarckii, Capitella teleta and Helobdella robusta. The C. teleta Dlx genes are closely linked in an inverted tail-to-tail orientation, reminiscent of the arrangement of vertebrate Dlx pairs, and gene conversion appears to have had a role in their evolution. The H. robusta Dlx genes, however, are not on the same genomic scaffold and display divergent sequences, while, if the P. lamarckii genes are linked in a tail-to-tail orientation they are a minimum of 41 kilobases apart and show no sign of gene conversion. No expression in P. lamarckii appendage development has been observed, which conflicts with the supposed conserved role of these genes in animal appendage development. These Dlx duplications do not appear to be annelid-wide, as the polychaete Platynereis dumerilii likely possesses only one Dlx gene.ConclusionsOn the basis of the currently accepted annelid phylogeny, we hypothesise that one Dlx duplication occurred in the annelid lineage after the divergence of P. dumerilii from the other lineages and these duplicates then had varied evolutionary fates in different species. We also propose that the ancestral role of Dlx genes is not related to appendage development.
Highlights
Dlx (Distal-less) genes have various developmental roles and are widespread throughout the animal kingdom, usually occurring as single copy genes in non-chordates and as multiple copies in most chordate genomes
It is thought that the ancestral chordate Dlx gene was linked to the Hox cluster, underwent a gene-specific duplication and inversion, and the Dlx gene pair was duplicated during the whole genome duplications that occurred in the vertebrate lineage [2,17,18]
All three of the genes are closely linked to CiHox13 and CiHox12
Summary
Dlx (Distal-less) genes have various developmental roles and are widespread throughout the animal kingdom, usually occurring as single copy genes in non-chordates and as multiple copies in most chordate genomes. It is thought that the ancestral chordate Dlx gene was linked to the Hox cluster, underwent a gene-specific duplication and inversion, and the Dlx gene pair was duplicated during the whole genome duplications that occurred in the vertebrate lineage [2,17,18]. In support of this hypothesis, it appears that Dlx, Dlx and Dlx form one paralogous group and that Dlx, Dlx and Dlx form another [17,19]. All three of the genes are closely linked to CiHox and CiHox
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