Development and dynamics of regional specialization within the syncytial epidermis of the rat tapeworm, Hymenolepis diminuta

Evolutionary developmental biology (evo-devo) of cestodes

Cestodes (tapeworms) have complex adaptations to their obligatory parasitic life-style. Among these adaptations, they show many evolutionary innovations in their development, including complex life-cycles with multiple hosts and life-stages, several independent origins of asexual reproduction, and the evolution of segmentation as a mean to generate massive reproductive output. Therefore, cestodes offer many opportunities for the investigation of the evolutionary origins of developmental novelties (evo-devo). However, cestodes have not been exploited as major models for evo-devo research due to the considerable technical difficulties involved in their study. In this review, a panoramic view is given of classical aspects, methods and hypothesis of cestode development, together with recent advances in phylogenetics, genomics, culture methods, and comparative analysis of cestode gene expression. Together with the availability of powerful models for related free-living flatworms, these developments should encourage the incorporation of these fascinating parasites into the first-line of evo-devo research.

cGMP secreted from the tapeworm Hymenolepis diminuta is a signal molecule to the host intestine

3',5'-Cyclic guanosine monophosphate (cGMP), a well-known intracellular second messenger, is released to the intestinal lumen by the tapeworm, Hymenolepis diminuta. Enzyme-linked immunosorbent assay analysis of tapeworm conditioned media shows that cGMP is released at a constant rate. Multidrug resistant (MDR) proteins are efflux transporters for cyclic nucleotides. Two MDR inhibitors, niflumic acid and zaprinast, inhibit cGMP secretion by tapeworms and change the cGMP localization within the tapeworm tegument, as assessed by immunochemistry. cGMP, normally present throughout the tapeworm tegumental cytoplasm, is absent from the outer cytoplasmic band upon treatment with inhibitors. Inhibition of cGMP secretion by colchicine indicates that cGMP secretion is cytoskeleton dependent. Binding studies of [3H]cGMP to ileal segments of intestine demonstrate 2 saturable, reversible, and high-affinity binding sites. These studies demonstrate that cGMP is secreted from the cestode via a cytoskeleton-dependent mechanism and MDR efflux transporters. In addition, cGMP reaching the intestinal lumen can bind to the mucosa via receptors for cGMP. These data, combined with earlier observations of cGMP altering intestinal motility and slowing lumenal transit, indicate that tapeworms alter the physiology of the host digestive process via the secretion and binding of extracellular cGMP to lumenal receptors in the host intestine.

Ultrastructure of the proglottid tegument (neodermis) of the cestode Echinophallus wageneri (Pseudophyllidea: Echinophallidae), a parasite of the bathypelagic fish Centrolophus niger

Ultrastructural data are provided on the tegument (or neodermis) of proglottids of the cestode Echinophallus wageneri Monticelli, 1890, the first representative of the family Echinophallidae (Pseudophyllidea), parasites of bathypelagic fish, studied using transmission and scanning electron microscopy. The surface of the ventral concave side of proglottids is covered with filiform microtriches about 1.7 microm long. Their glycocalyx, although very thick, is less extensively developed compared to that on digitiform microtriches localized on the dorsal side of the proglottids, which is also covered with filiform microtriches. The digitiform microtriches of the convex dorsal side are about 0.6 microm long, with a very short, rounded spine and the extraordinarily extensive glycocalyx seen as flocculent material. Short digitiform microtriches of E. wageneri seem to differ from microthrix types previously reported in other cestodes by transmission electron microscopy. The posterodorsal margin of all proglottids is typical in possessing a transverse band of large spiniform, tusk-shaped microtriches with a very long spine (approximately 13 microm in length), merged with filiform microtriches. Marked regional differences found in the morphology and distribution of microtriches on the proglottids of E. wageneri may be related to the different functions of the individual parts of the strobila because of the curling of the tapeworm body within the intestine of its fish host.

Structure and diversity of cestode epithelia

Eucestodes have a simple aceolomate body structure and are conservative in terms of the numbers and nature of their cell types. Nevertheless, the cestodes form a diverse group with many strikingly different forms distinguished by the structure of their holdfasts, sexual tissues and embryos. These morphological adaptations have their origins in subtle variations in the structure of their cells and extracellular matrices. This review is concerned with the biology of eucestode epithelia and examines their structure and functions, interrelationships with other tissues, and gives insight into how their components are modified among the many taxa. Three features of cestode epithelia, namely, the occurrence of regional specialisation, microtriches and secretory components, are described. In addition, evidence is presented to suggest that some cestode epithelia are involved in developmental processes such as the nurture of embryos and maintenance of surrounding tissues.

Ultrastructure of oncosphere and early stages of metacestode development of Echinococcus granulosus

The ultrastructure of the oncospheres and developing metacestodes in vitro of Echinococcus granulosus was studied with emphasis on the origin of the laminated layer. The activated oncospheres measured 28 microns (S.D. = 1.83), and by day 5 of in vitro culture the metacestodes attained diameters up to 52 microns (S.D. = 2.66). The oncospheral plasma membrane of the tegument appeared to be formed by a microtubular cytoskeleton arranged in a predetermined pattern. By day 2 there were three main types of vesicles in the perikaryon: Vd, Vg1 and Vg2. Vesicles appeared to be synthesized in the perikaryon and continuously transported to the periphery, where the Vd vesicles could contribute to the ground substance of the syncytial tegument. We suggest that the Vg1 and Vg2 vesicles contribute to the laminated layer where, by day 5, they were seen in increased density and forming aggregations on the outer border.

The effect of dimethylsulfoxide on the tegumental brush border of the cestode Hymenolepis diminuta

Dimethyl sulfoxide (DMSO), commonly used for cryoprotection or for the solvation of cytoskeleton-modifying drugs, causes changes in the topology of the plasma membrane of the tegumental brush border in the tapeworm Hymenolepis diminuta; however, relatively long exposures of high concentrations are required. In tapeworms treated with DMSO concentrations of greater than or equal to 1% in the present study, the interaction of the tegumental surface membrane with the underlying cytoskeleton may have been disrupted at focal points in the brush border, resulting in a partial loss of the membrane anchoring required for the structural integrity of the brush border. Blebbing of the tegumental surface was prominent only after exposure to 1% DMSO for 20 h in in vitro culture with RPMI 1640, and vesiculation of the membrane along the microvillar (microtriche) shafts, which may have been related to the in vitro conditions, was amplified by the presence of concentrations of greater than or equal to 1% DMSO in the incubation medium. The tegumental response to DMSO was not uniform but regional, consistently appearing to be more prevalent on the distal aspects of each proglottid rather than on the edge proximal to the scolex. Blebbing and vesiculation were not seen on the basal aspect of the tegument, including the basal ectocytoplasmic plasma membrane, the perikarya, and the internuncial processes. Microvillar core bundles of actin microfilaments persisted following 8 h in vitro exposure to all three concentrations of DMSO tested (0.1%, 1%, 5%); however, only in tapeworms that were treated in vitro with 5% DMSO for greater than or equal to 8 h did core microfilament bundles appear to lose the rigidly straight and parallel organization characteristic of control tapeworms that were incubated either in the absence of DMSO or with 0.1% DMSO. Other components of the brush border cytoskeleton (i.e., microvillar caps, junctional tubules, and tunics) appeared unaffected by DMSO except at foci where blebbing occurred.(ABSTRACT TRUNCATED AT 250 WORDS)