Actin cytoskeleton in adults and metacercariae of Brachylaima sp

Abstract

Experimental adults and natural metacercariae of Brachylaima sp. (Digenea: Brachylaimidae) were processed for transmission and scanning electron microscopy, for tetramethyl rhodamine isothiocyanate phalloidin fluorescence, conventional and confocal microscopy and for monoclonal anti-actin antibody immunoelectron microscopy, to describe the ultrastructural features of the tegument and to localize actin in several regions of the body. The general body tegument is spinous and contains membrane-bound disc-shaped biconcave vesicles in adults and metacercariae. Spines are flat and apically indented in the adult. A thick glycocalyx covers the body of the metacercaria. Direct fluorescence revealed filamentous actin in the spines and the subtegumental musculature of the adult. The subtegumental musculature comprises two systems consisting of an outer circular layer and an inner layer composed of cross-linked longitudinal and diagonal fibres. Immunoreactivity in adults and metacercariae revealed the presence of actin in the spines and subtegumental musculature but not in the tegumental matrix, interstitial fibrous material nor the parenchyma. Actin was detected in the dense collar and bulb matrix of the tegumental ciliated sensilla and, for the first time, in the apical cytoplasmatic projections of the digestive cell of the adult.