The
tegumental cytoskeleton of Opisthorchis viverrini was observed using both
conventional transmission electron microscopy and Triton X-100 extraction.
The cytoskeletal elements of the newly excysted juveniles, first-week and
adult stages are composed of 2 components: firstly, the network of knobbed
fibres designated as microtrabeculae which form the principal scaffold of
the cytoplasm; and secondly, the microtubules. The microtrabeculae are more
densely packed in the newly excysted juveniles and become less densely packed
later in the first-week and adult stages. Generally, their compactness in
the tegument of each stage is higher in the apical and middle zones than
in the basal zone. The results from extraction by Triton X-100 suggest that
the microtrabeculae may be composed, at the primary level, of thin and straight
fibres, partly coiled up to form knobbed fibres, which are highly cross-linked
at the secondary level. At the tertiary level, these knobbed fibres may
be coiled up further and form closely aggregated globules that appear as
dense dots in cross-section. Most microtubules are confined within the tegumental
cells' processes and splay out in the basal zone of the tegument. In addition,
there are condensed laminae of cytoplasm with intermittent dense plaques
underlining the outer membrane, with microtrabecular fibres inserting into
them. This organization may help to stabilize the outer membrane and preserve
the surface contour. Along the inner membrane of the tegument, there are
hemidesmosomes distributed at regular intervals, with fine fibres radiating
out from them to intertwine with the microtrabecular network, which may
help to anchor the tegument to the basal lamina. Spines, which exist mainly
in the newly excysted juveniles, appear as a crystalline lattice structure
whose bases are firmly fused to the inner membrane.