Meeting Abstract
The compact body plan of tardigrades evolved through the loss of several body segments. The metazoan gut is an unsegmented structure divided into foregut, midgut and hindgut regions. Because the gut is an unsegmented structure, we hypothesized that the loss of body segments in tardigrades did not coincide with a loss of a region of the gut. To test this hypothesis, we analyzed three genes that control gut development during embryogenesis in other animals, in the tardigrade Hypsibius exemplaris. These genes are forkhead, a marker of foregut and hindgut identity; gata-1/2/3, an additional marker of foregut identity; and gata-4/5/6, a marker of midgut identity. We predicted that these genes would exhibit regionalized expression patterns in the developing tardigrade gut, as they do in other animals. We identified orthologs of these genes in the genome of H. exemplaris. Gene expression patterns were visualized using in-situ hybridization during a late embryonic period. Forkhead was expressed in an anterior and posterior region of the developing gut in H. exemplaris embryos, suggesting that foregut and hindgut regions are retained in tardigrades. However, gata-1/2/3 was not expressed in the gut, which challenges the retention of foregut identity in tardigrades. Future studies will determine whether gata-1/2/3 is co-expressed with forkhead in an anterior region of the gut during earlier stages of gut development, as predicted if the foregut region is retained by tardigrades, and whether gata-4/5/6 is expressed in a middle region of the developing gut, as predicted if the midgut region is retained by tardigrades.
