An IQGAP-related gene is activated during tentacle formation in the simplemetazoan Hydra

Differentiation of body column epithelial cells into tentacle epithelial ce lls in Hydra is accompanied by changes in both cell shape and cell-cell con tact. The molecular mechanism by which epithelial cells acquire tentacle ce ll characteristics is unknown. Here we report that expression of a Hydra ho mologue of the mammalian IQGAP1 protein is strongly upregulated during tent acle formation. Like mammalian IQGAP, Hydra IQGAP1 contains an N-terminal c alponin-homology domain, IQ repeats and a conserved C terminus. In adult po lyps a high level of Hydra IQGAP1 mRNA is detected at the basis of tentacle s. Consistent with a role in tentacle formation, IQGAP1 expression is activ ated during head regeneration and budding at a time when tentacles are emer ging. The observations support the previous hypothesis that IQGAP proteins are involved in cytoskeletal as well as cell-cell contact rearrangements.