Immunocytochemical localization of actin inToxoplasma gondii

The localization of actin in the trophozoites ofToxoplasma gondii was examined by means of immunogold staining for electron microscopy. The thin-sectioned specimens were incubated with the IgG fraction of polyclonal antibodies raised againstAscaris body-wall smooth-muscle actin following colloidal gold-conjugated protein A. Electron-dense gold particles were confined to the anterior polar region in the trophozoites: they were found in the conoid, preconoidal rings, possibly in the polar ring, and in the space between the anterior terminal of the inner membrane complex and conoid. The present experiments also suggest interactions of actin with subpellicular microtubules, leading to speculation that the association of actin with microtubules provides a link to myosin, a potential source of power for microtubuledependent movements.