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Abstract Background 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. 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. Results Two 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. Conclusions On 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.

Primary (nonmotile) cilia are currently enjoying a renaissance in light of novel ascribed functions ranging from mechanosensory to signal transduction. Their importance for key developmental pathways such as Sonic Hedgehog (Shh) and Wnt is beginning to emerge. The function of nodal cilia, for example, is vital for breaking early embryonic symmetry, Shh signaling is important for tissue morphogenesis and successful Wnt signaling for organ growth and differentiation. When ciliary function is perturbed, photoreceptors may die, kidney tubules develop cysts, limb digits multiply and brains form improperly. The etiology of several uncommon disorders has recently been associated with cilia dysfunction. The causative genes are often similar and their cognate proteins certainly share cellular locations and/or pathways. Animal models of ciliary gene ablation such as Ift88, Kif3a, and Bbs have been invaluable for understanding the broad function of the cilium. Herein, we describe the wealth of information derived from the study of the ciliopathies and their animal models.