Meeting Abstract
A highly conserved mechanism typically patterns the through-gut of nephrozoans. This mechanism is predicted to pattern the gut of tardigrades. However, tardigrades are highly simplified and miniaturized, presenting the possibility that the developmental mechanism that patterns the tardigrade gut is also secondarily simplified. Simplification of gut patterning could be identified by the loss of an ancestral gut patterning gene, the loss of a gene’s function in patterning the gut, or by reduction in the degree to which gut patterning genes exhibit regionalized expression patterns during gut development. We investigated the genomes of two representatives of Tardigrada—Hypsibius exemplaris and Ramazzottius varieornatus. We identified single orthologs of forkhead (fkh), gata456,, orthodenticle (otd), caudal (cad), goosecoid, hnf-4, even-skipped, and fgf8/17/18—genes that play important roles in gut patterning in other nephrozoans. However, we were unable to identify orthologs of foxq2, brachyury, nk2.1, or wingless, genes that typically pattern the through-gut of other nephrozoans, suggesting that these genes were lost in the tardigrade lineage. We have investigated the expression patterns of otd, fkh, gata456, and cad in H. exemplaris embryos. He-otd and He-cad were expressed in the anterior and posterior of the developing body axis in H. exemplaris embryos, as predicted. He-fkh is expressed throughout the developing gut, as predicted. However, we detected expression of He-gata456 broadly throughout the developing gut, rather than it being restricted to the developing midgut as it is in other nephrozoans. Together, our results provide preliminary evidence of a simplified gut patterning mechanism in Tardigrada.
