ACTIN IN SPERMATOZOON OF A SOFT TICK, ARGAS-(A)-POLONICUS (IXODIDA, ACARI)

Distribution of actin in spermatozoa before (prospermia) and after (sp ermiophores) cell eversion process in a soft tick, Argas (A.) polonicu s, was studied by phalloidin- rhodamine fluorescence and immunogold la belling methods. F-actin was mainly localized at the cortical cytoplas m surrounding the vacuole in prospermia and along the periphery of spe rmiophores. A further localization of actin was in the cytoplasm in th e ''head'' and adjacent region both in prospermium and spermiophore. I mmunogold labelling revealed the presence of actin in the cytoplasm of whole spermatozoon with higher concentration in the ''head'' region. In the peripheral cytoplasm, however, actin was found in the material coating electron-dense fibres. The fibres themselves and cell protrusi ons were not labelled suggesting that F-actin was localized around den se fibres. Of two distinct pools of F-actin found in the tick spermato zoa, the one located in the subplasmalemmal cytoplasm is supposedly re sponsible for the gliding movement, whereas that filling the anterior tapered end including ''head'' - may be involved in contortional movem ents of that region. The participation of actin-based mechanism in for ward gliding of spermiophores was confirmed in experiments with cytoch alasin B. The contribution of actin to prospermium vacuole opening and subsequent cell eversion is suggested.