Differential Expression Ofbmpinhibitorsgremlinandnoggininhydrasuggests Distinct Roles During Budding And Patterning Of Tentacles

Background Mechanisms regulating BMP and Wnt pathways and their interactions are not well studied inHydra. Results We report identification of BMP inhibitorgremlin, comparison of its expression with that ofnogginand possible antagonism between Wnt and BMP signaling inHydra.Gremlinis expressed in body column with high levels in budding region and in early buds.Noggin, on the other hand, is expressed in the hypostome, base of tentacles, lower body column, and basal disc. During budding,nogginis expressed at the sites of tentacle emergence. This was confirmed in ectopic tentacles in polyps treated with alsterpaullone (ALP), a GSK-3 beta inhibitor that leads to upregulation of Wnt pathway. RT-PCR data show that upregulation of Wnt is accompanied by downregulation ofbmp 5-8bthoughnogginandgremlinremain unaltered till 24 hours. Conclusions Different expression patterns ofgremlinandnogginsuggest their roles in budding and patterning of tentacles, respectively. Further,bmp 5-8binhibition by activated Wnt signaling does not directly involvenogginandgremlininHydra. Our data suggest that Wnt/BMP antagonism may have evolved early for defining the oral-aboral axis, while the involvement of BMP antagonists during axial patterning is a recent evolutionary acquisition within the Bilateria lineage.