Genes encoding cytoplasmic intermediate filament proteins of vertebrates revisited: Identification of a cytoplasmic intermediate filament protein in the sea anemone Nematostella

The cytoskeleton is crucial in determining cell architecture, division, motility, transport processes and in local control of signal transduction. Relatives of actin and tubulin are expressed in all phyla, underlining the fundamental importance of conserved cytoskeletal functions. Intermediate filament proteins have evolved in parallel with tissue diversity in the animal kingdom, likely from the demand to adapt one class of cytoskeletal proteins to cell type-restricted functions. Up to now, the evolutionary origin of cytoplasmic intermediate filament proteins remains unknown. Using a known gene encoding a cytoplasmic intermediate filament protein from the hemichordate Saccoglossus kowalevskii, we have identified the first corresponding gene in the sea anemone Nematostella, tentatively named cytovec. Our data reveal a relationship of cytovec with Hydra vulgaris nematocilins A and B that also lack a CAAX box. In light of additional recent findings, our data show that cytoplasmic intermediate filament genes are present in the common ancestor of Cnidaria and Bilateria.