Meeting Abstract
Tardigrada consists of two lineages—Heterotardigrada and Eutardigrada. All tardigrades are microscopic animals with tiny legs. To understand the evolution of tardigrade legs, we have analyzed the leg gap genes, Distal-less, dachshund, and homothorax/extradenticle, which specify distal, intermediate, and proximal appendage domains in arthropods. In Hypsibius exemplaris, a representative of Eutardigrada, Distal-less is broadly expressed across the appendage bud during development. Homothorax/extradenticle do not specify proximodistal appendage domains in this species. Dachshund is not found in the genomes of H. exemplaris or a second representative of Eutardigrada, Ramazzottius varieornatus. These results indicate that tardigrade legs evolved by the loss of proximal and intermediate regions. To further characterize the evolution of the proximodistal axis of tardigrades, we recently sequenced the genome of Batillipes pennaki, a representative of Heterotardigrada. Consistent with our earlier study of eutardigrade genomes, orthologs of Distal-less, homothorax, and extradenticle are present in the genome of B. pennaki, and an ortholog of dachshund is not present in the genome. In order to further characterize the role of Distal-less in tardigrade leg development, we have identified orthologs of genes that are either upstream or downstream of Distal-less during leg development in arthropods. We have identified orthologs of BarH1, clawless, decapentaplegic, rotund, and zfh2 in both eutardigrade and heterotardigrade genomes. Additionally, we have identified orthologs of apterous, aristaless, Lim1, nubbin, and spineless in eutardigrade genomes. Results of preliminary analyses of the developmental roles of candidate appendage patterning genes in H. exemplaris will be shown.
