Actin in spermatozoon of a soft tick, Argas (A.) polonicus (Ixodida, Acari)

Distribution of actin in spermatozoa before (prospermia) and after (spermiophores) cell eversion process in a soft tick, Argas (A.) polonicus, was studied by phalloidin-rhodamine fluorescence and immunogold labelling methods. F-actin was mainly localized at the cortical cytoplasm surrounding the vacuole in prospermia and along the periphery of spermiophores. A further localization of actin was in the cytoplasm in the "head" and adjacent region both in prospermium and spermiophore. Immunogold 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 protrusions were not labelled suggesting that F-actin was localized around dense fibres. Of two distinct pools of F-actin found in the tick spermatozoa, the one located in the subplasmalemmal cytoplasm is supposedly responsible for the gliding movement, whereas that filling the anterior tapered end including "head"--may be involved in contortional movements of that region. The participation of actin-based mechanism in forward gliding of spermiophores was confirmed in experiments with cytochalasin B. The contribution of actin to prospermium vacuole opening and subsequent cell eversion is suggested.