Tegumental cells

Fig. 2.2. Structural analogy between the tegumental cells of cestodes (right) and the mammalian intestinal epithelium (left) both of which show surface amplification (see text).

The terminology in the literature is confusing. Terms used for the outer (nucleate) zone include syncytial layer, surface layer, distal cytoplasm, tegument and for the inner (nucleated) zone perikarya, proximal layer, tegumental cells, cytons, perinuclear cytoplasm. Bearing in mind that descriptive terms are more likely to be remembered and used correctly than non-descriptive words, the terms distal cytoplasm and proximal cytoplasm, which are well established in the literature, are used in this text, for these zones. The term tegumental cytons is used for the basic cells which make up the syncytial epithelium (Fig. 2.1). 

As alluded to above, because the eventual consequence of tegumental signal reception and transduction will likely be the triggering of molecular or biochemical pathways in non-tegumentary cells or tissues, the... 

Hamdan et al. (2002) describe another biogenic amine-responsive GPCR in the tegument of S. mansoni, which specifically binds to and is activated by histamine. This cloned receptor shares approximately 30% amino acid sequence homology with other major amine GPCRs, and, when transfected into mammalian cells exhibited the following characteristics ... 

Fujino, T., Fried, B. and Takamiya, S. (1 995) Cytochemical localization of cytochrome c oxidase activity in mitochondria in the tegument and tegumental and parenchymal cells of the trematodes Echinostoma trivolvis, Zygocotyle lunata, Schistosoma mansoni, Fasciola gigantica and Paragonimus ohirai. Journal of IHelminthology 69, 1 95-201. 

It has been demonstrated by numerous workers that the majority of benzimidazoles inhibit the microtubulin [6-11 ] of tegumental or intestinal cells of nematodes or cestodes through degeneration of these cells. This mechanism is now well accepted as the mode of action for benzimidazole derivatives. 

Hydrocarbons (HC) act as pheromones in a variety of orders including the Dictyoptera (Jurenka et al., 1989 Schal et al., 1994 Lihoreau and Rivault, 2009), Coleoptera (Ginzel et al., 2003, 2006), Hymenoptera (Howard, 1993 Le Conte and Hefetz, 2008), Diptera (Carlson et al., 1971 Antony and Jallon, 1982 Blomquist et al., 1987) and several lepi-dopteran species (Roelofs and Carde, 1971 Millar, 2000). In most insects, they are present on the cuticle and are synthesized in large cells called oenocytes located within or under the abdominal integument (Diehl, 1975 Ferveur et al., 1997 Schal et al., 1998 Fan et al., 2003). In Lepidoptera, their synthesis occurs in tissues associated with the abdominal tegument (possibly oenocytes), and they are then released into a sex pheromone gland (Schal et al., 1998). 

That the sodium pump operates in cestodes has been clearly shown in H. diminuta and the same inhibitors (ouabain and phlorizin) which inhibit the system in the mucosal cells are also effective in cestodes (Figs 2.2 and 2.4). One major difficulty, however, in applying the intestinal cell model to the cestode tegument is that the enzyme Na+/K+-ATPase, which is involved in the former, has only been identified with certainty in E. granulosus (491) and not in any other species (878). 

Fig. 2.12. Scolex of Diphyllobothrium dendriticum plerocercoid. The neural elements have been labelled with growth hormone releasing factor (GRF), a vertebrate neuropeptide. In the main nerve cord (n) one GRF-immunoreactive cell body can be seen (large arrow) in the peripheral nervous system (P) several GRF-immunoreactive cells bodies occur (large arrows). The small arrows point to nerve terminals beneath the basal lamina of the tegument along the inner border of the bothridia. Sections stained with Stemberger s immunoperoxidase-antiperoxidase (PAP) technique. (Courtesy Dr Margaretha K. S. GustafFson.)...

The alkaloid colchicine binds tightly to tubulin and this characteristic has been used (Fig. 6.1) to isolate a tubulin-like fraction from H. diminuta, with properties similar to tubulin from other organisms. Furthermore, colchicine affects the qualitative distribution of [3H]proline-incorporated protein in this worm, with label accumulating in the parenchyma (195). This suggests that colchicine inhibits translocation in the tegument and provides evidence that microtubules within the internuncial processes facilitate movement of cell products from tegumentary cytons (Chapter 2) to the body surface for subsequent release. 

Ca2 +-ATPase has been used as an enzymic marker for the brush border of H. diminuta, although its precise function is open to question. Two forms of this enzyme occur within the tegument of the parasite. One appears to be calmodulin dependent and is active at a higher pH than the other (Table 6.2). Calmodulin appears to be a ubiquitous Ca2 + receptor which plays a part in most of the Ca2+-regulated processes that have been studied in eukaryotic cells. It is a highly conserved protein, so it is not surprising that... 

In many places, the plasmalemma between the microtriches and that of the epithelial cells of the host intestine were lacking, so that the matrix of the tegument was in direct contact with the cytoplasm of the host cells. Lysosomes were observed in the substance surrounding the microtriches embedded in the host cytoplasm. 

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