Actin-binding protein tropomodulin-1 is necessary for basal constriction formation and bud detachment in Hydra...

Tropomodulins (TMODs) are a group of proteins that stabilize the actin filament network by capping the slow-growing end of F-actin. Although their roles in tissue morphogenesis have been extensively studied in triploblastic organisms, their function in diploblastic Hydra remained unexplored. This study identified that in Hydra, TMOD1 expression is strongly upregulated in ectodermal cells at the parent-offspring junction during basal constriction formation and bud detachment. Notably, siRNA-mediated TMOD1 knockdown inhibits basal constriction formation, a pre-requisite morphological event for bud detachment. TMOD1 knockdown polyps show fragmented stress fibers and altered cell morphology adjacent to the basal constriction site. Finally, pharmacological studies showed that FGFR signaling is necessary for TMOD1 expression. Collectively, our results establish that Hydra TMOD1 is an FGFR-ERK2 signaling-regulated gene that is exclusively expressed in the epitheliomuscular ectodermal cells at the parent-offspring junction and is essential for bud separation from the parent Hydra polyp by promoting F-actin polymerization/stabilization.