Contractile eukaryotic flagella: Centrin is involved

Summary Isolated transverse flagella ofPeridinium inconspicuum (Dinophyceae) undergo a rapid Ca²⁺-induced (50M Ca²⁺) contraction in the absence of exogenous ATP. Longitudinal flagella from the same species do not contract under these conditions. Contraction leads to a supercoiling of the axoneme and a shortening of the paraxonemal fiber that accompanies the axoneme over most of its length. Using a polyclonal antibody generated against centrin, a 20 kDa Ca²⁺-modulated contractile protein of striated flagellar roots of the green flagellateTetraselmis striata, we have found that the paraxonemal fiber in transverse flagella of three taxa ofDinophyceae is immunoreactive by indirect immunofluorescence. The localization of the antigen in the paraxonemal fiber of transverse flagella was confirmed by two-colour double immunofluorescence using monoclonal mouse-anti--tubulin for identification of the axoneme. No structure was immunoreactive to anticentrin in the longitudinal flagella of all taxa. Electrophoretic and immunoblot analysis of isolated flagella ofP. inconspicuum show that the antigen is a 21 kDa protein, indicating that it is either centrin or a closely related protein. We conclude that centrin confers contractility to the transverse flagellum of dinoflagellates and possibly to other contractile eukaryotic flagella.Abbreviations ASP-H artificial seawater medium with Hepes-buffer - BSA bovine serum albumine - DTT dithiothreitol - EGTA ethylene glycol bis(2-amino-ethylether)tetraacetic acid - FITC fluorescein isothiocyanate - MT buffer microtubule stabilizing buffer - PBS phosphate buffered saline - SDS sodium dodecyl sulfate - TLCK N-p-tosyl-l-lysine chloromethyl ketone - TRITC tetramethylrhodamine isothiocyanate