Actin isoforms in amphioxus Branchiostoma lanceolatum

Abstract 

Actin is a highly conserved cytoskeletal protein that is ubiquitous in all eukaryotes. Little is known about actin expression in amphioxus, the closest living relative of the vertebrates. In the present study, involving Western blotting and indirect immunofluorescence, we report the characterization and localization of various actin isoforms in amphioxus (Branchiostoma lanceolatum) tissues. Three antibodies against vertebrate actins were used: a polyclonal antibody recognizing β-cytoplasmic actin (anti-β actin), a monoclonal antibody against sarcomeric actins (anti-αSR-1), and a monoclonal antibody specific for α-smooth actin (anti-αSM-1). Western blot analysis of amphioxus extracts immunodecorated with these antibodies showed a 43-kDa-positive band co-migrating with respective controls. The amphioxus isoactin expression patterns recognized by these antibodies were similar to those of vertebrates, i.e., anti-β actin showed positive staining mainly in non-muscle cells, anti-αSR-1 labelled dorsolateral myotomal muscles, and anti-αSM-1 stained ventral muscles. These results demonstrate that at least two muscle actins are present in amphioxus, suggesting that muscle actin gene duplication events began before vertebrate divergence from the amphioxus lineage.