ACTIN ISOFORMS IN AMPHIOXUS BRANCHIOSTOMA-LANCEOLATUM

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 amp hioxus (Branchiostoma lanceolatum) tissues. Three antibodies against v ertebrate actins were used: a polyclonal antibody recognizing beta-cyt oplasmic actin (anti-beta actin), a monoclonal antibody against sarcom eric actins (anti-alpha SR-1), and a monoclonal antibody specific for alpha-smooth actin (anti-alpha SM-1). Western blot analysis of amphiox us extracts immunodecorated with these antibodies showed a 43-kDa-posi tive band co-migrating with respective controls. The amphioxus isoacti n expression pat terns recognized by these antibodies were similar to those of vertebrates, i.e., anti-beta actin showed positive staining m ainly in non-muscle cells, anti-alpha SR-1 labelled dorsolateral myoto mal muscles, and anti-alpha SM-1 stained ventral muscles. These result s demonstrate that at least two muscle actins are present in amphioxus , suggesting that muscle actin gene duplication events began before ve rtebrate divergence from the amphioxus lineage.