Observations on the attachment by the monogenean, Anoplodiscus australis, to the caudal fin of Acanthopagrus australis

The unarmed haptor of Anoplodiscus australis erodes the epidermis and attaches to the basal lamina above the stratum compactum in the caudal fin of Acanthopagrus australis by an eosinophilic, weakly PAS-positive and strongly toluidine blue-positive secretion. Ultrastructural evidence shows that the adhesive secretion, in the form of rod-shaped bodies, is produced by subtegumentary cells that connect by ducts to the thin, ventral syncytial tegument of the haptor; these bodies pass into the tegument, then coalesce in the host-parasite interface. This means of attachment has developed by an enhancement and regional specialization of the subtegumentary secretory cells associated with a syncytial tegument in monogeneans and some other platyhelminths. The available evidence indicates that the adult parasite is permanently attached.     

Synthesis of macromolecules by the epithelial surfaces of Schistosoma mansoni: an autoradiographic study.

The use of tritiated leucine as a marker for protein synthesis and of tritiated glucosamine as a marker for polysaccharide/glycoprotein synthesis, is described. Adult worms were pulse-labelled by incubation in medium containing the substrate. Labelled worms were then incubated in chase medium, without labelled substrate, for varying lengths of time before fixation. The distribution of label which had been incorporated into macromolecules in the worm tissues, was examined by light and electron microscope autoradiography. It was estimated that the tegument and tegument cell bodies were the source of 67--80%, and the gut epithelium of 20--30%, of exportable leucine-containing protein. Conversely, the gut epithelium was the source of 72%, and the tegument cells 28%, of exportable glucosamine-containing polysaccharide. The specific activity of labelled protein reached a peak in the tegument cytoplasm after 1.5 h of chase incubation. Half of the labelled protein was secreted into the worm's environment by 3 h of chase incubation. The half-life of secretory protein in gut cells appears to be around 2 h. Labelled protein disappears from the gut lumen relatively rapidly but labelled polysaccharide remains in the lumen at high specific activity for at least 24 h. The major carbohydrate labelled may be the glycocalyx on the luminal surface of the gut epithelial cells. The results suggest that the bulk of worm secretions have a rapid turnover with a half-life of a few hours. Against this background of rapid mass secretion a slower process of membrane turnover would be difficult to detect and quantitatively small.     

Changes in the monocercus cercomer in the cysticercoid cavity and the hemocoel of the nonspecific host

In order to elucidate the functional role of cercomer in larvae of the monocercus type their transplantation from the specific host Chironomus obtusidens to Gammarus lacustris was conducted. At early stages after the transplantation proceeds an increase in the functional activity of the tegument of follicles of the cercomer followed by their complete destruction in 3 or 4 days. On the surface of the exocyst membrane an adhesion of the host's haemocytes occurs, which becomes more distinct in 3-4 days when the process acquires a character of local encapsulation. Within the same period, in the places of haemocytes aggregation, a local resorption of the exocyst external membrane takes place. Later intensification of the host response to transplant is associated with the destruction of follicles of the cercomer. In one case the occurrence of follicles of the cercomer in the cavity of cysticercoid was observed that is caused by the microbe affection of the latter. In the zone of contact of the tegument of scolex and neck with follicles of the cercomer an increased secretion (the microapocrine type) of the tegument, disturbance of the microvillous tegument of the cercomer's follicles and their destruction are observed. Incompatibility of the tegument of definitive departments and cercomer, which arises during differentiation of larvae, is supposed to affect the formation of scolex invagination in the evolution of larvae of Hymenolepis.     

Biochemical and structural characterization of the capsid-bound tegument proteins of human cytomegalovirus

Human cytomegalovirus (HCMV) is the most genetically and structurally complex human herpesvirus and is composed of an envelope, a tegument, and a dsDNA-containing capsid. HCMV tegument plays essential roles in HCMV infection and assembly. Using cryo electron tomography (cryoET), here we show that HCMV tegument compartment can be divided into two sub-compartments: an inner and an outer tegument. The inner tegument consists of densely-packed proteins surrounding the capsid. The outer tegument contains those components that are loosely packed in the space between the inner tegument and the pleomorphic glycoprotein-containing envelope. To systematically characterize the inner tegument proteins interacting with the capsid, we used chemical treatment to strip off the entire envelope and most tegument proteins to obtain a tegumented capsid with inner tegument proteins. SDS-polyacrylamide gel electrophoresis analyses show that only two tegument proteins, UL32-encoded pp150 and UL48-encoded high molecular weight protein (HMWP), remains unchanged in their abundance in the tegumented capsids as compared to their abundance in the intact particles. Three-dimensional reconstructions by single particle cryo electron microscopy (cryoEM) reveal that the net-like layer of icosahedrally-ordered tegument densities are also the same in the tegumented capsid and in the intact particles. CryoET reconstruction of the tegumented capsid labeled with an anti-pp150 antibody is consistent with the biochemical and cryoEM data in localizing pp150 within the ordered tegument. Taken together, these results suggest that pp150, a betaherpesvirus-specific tegument protein, is a constituent of the net-like layer of icosahedrally-ordered capsid-bound tegument densities, a structure lacking similarities in alpha and gammaherpesviruses.     

Analysis of the interaction between the essential herpes simplex virus 1 tegument proteins VP16 and VP1/2

The incorporation of tegument proteins into the herpes simplex virus 1 (HSV-1) virion during virion assembly is thought to be a complex, multistage process occurring via numerous interactions between the tegument and the capsid, within the tegument, and between the tegument and the envelope. Here, we set out to examine if the direct interaction between two essential tegument proteins VP1/2 and VP16 is required for connecting the inner tegument with the outer tegument. By using glutathione S-transferase (GST) pulldowns, we identified an essential role of lysine 343 in VP16, mutation of which to a neutral amino acid abrogated the interaction between VP1/2 and VP16. When the K343A substitution was inserted into the gene encoding VP16 (UL48) of the viral genome, HSV-1 replicated successfully although its growth was delayed, and final titers were reduced compared to titers of wild-type virus. Surprisingly, the mutated VP16 was incorporated into virions at levels similar to those of wild-type VP16. However, the analysis of VP16 on cytoplasmic capsids by fluorescence microscopy showed that VP16 associated with cytoplasmic capsids less efficiently when the VP16-VP1/2 interaction was inhibited. This implies that the direct interaction between VP1/2 and VP16 is important for the efficiency/timing of viral assembly but is not essential for HSV-1 replication in cell culture. These data also support the notion that the incorporation of tegument proteins into the herpesviruses is a very complex process with significant redundancy.     

Ultrastructure of the male accessory ducts and prostate gland of Diclidophora merlangi (Monogenoidea)

The vas deferens, seminal vesicle, penis and common genital atrium of the monogenean, Diclidophora merlangi are lined by a very flat, lamellate epithelium. The structure is apparently syncytical, although nuclei or perikaryons have not been observed. The epithelium extends to just inside the gonopore where a septate desmosome marks the union with body tegument. There is minor regional variation in structure. The terminal portion of the seminal vesicle and the penis lumen are lined in part by the luminal cytoplasm of the prostate gland which surrounds this part of the reproductive tract. The prostate gland cells are synthetically active and produce a characteristic secretory body that is released either singly by exocytosis, involving membrane fusion, or in bulk via apocrine secretion. The secretion is acidophilic, PAS-positive and reactive for protein. The penis is sucker-like in structure and armed with a ring of 16 genital hooklets. Cilia have not been observed in any part of the male reproductive tract, and sense receptors are not apparent in the tegument surrounding the gonopore.     

鱊头槽绦虫原尾蚴皮层的超微结构观察

利用透射电镜观察了头槽绦虫 (Bothriocephalusacheilognathi)原尾蚴皮层的超微结构。头槽绦虫原尾蚴的皮层为典型的合胞体结构。皮层表面有浓密的微毛与少量的突起。与成虫相比 ,原尾蚴的微毛长而且粗 ,呈现单态性 ,推测在进入终末宿主的过程中有脱落和再生现象。突起分布在头部与体侧 ,含有较少的电子致密颗粒。在原尾蚴皮层细胞质中观察到三种腺细胞的分泌过程 ,即顶分泌、外分泌和微分泌过程。原尾蚴身体后部观察到尾钩和穿刺腺管道的开口。在核周区和纤维层下可见发育较好的环肌与纵肌。本文还对原尾蚴皮层突起的功能进行了探讨。     

In rat dorsal root ganglion neurons,herpes simplex virus type 1 tegument forms in the cytoplasm of the cell body

The herpes simplex virus type 1 (HSV-1) tegument is the least understood component of the virion, and the mechanism of tegument assembly and incorporation into virions during viral egress has not yet been elucidated. In the present study, the addition of tegument proteins (VP13/14, VP16, VP22, and US9) and envelope glycoproteins (gD and gH) to herpes simplex virions in the cell body of rat dorsal root ganglion neurons was examined by immunoelectron microscopy. All tegument proteins were detected diffusely spread in the nucleus within 10 to 12 h and, at these times, nucleocapsids were observed budding from the nucleus. The majority (96%) of these nucleocapsids had no detectable label for tegument and glycoproteins despite the presence of tegument proteins in the nucleus and glycoproteins adjacent to the nuclear membrane. Immunolabeling for tegument proteins and glycoproteins was found abundantly in the cytoplasm of the cell body in multiple discrete vesicular areas: on unenveloped, enveloped, or partially enveloped capsids adjacent to these vesicles and in extracellular virions. These vesicles and intracytoplasmic and extracellular virions also labeled with Golgi markers, giantin, mannosidase II, and TGN38. Treatment with brefeldin A from 2 to 24 h postinfection markedly inhibited incorporation into virions of VP22 and US9 but to a lesser degree with VP16 and VP13/14. These results suggest that, in the cell body of neurons, most tegument proteins are incorporated into unenveloped nucleocapsids prior to envelopment in the Golgi and the trans-Golgi network. These findings give further support to the deenvelopment-reenvelopment hypothesis for viral egress. Finally, the addition of tegument proteins to unenveloped nucleocapsids in the cell body allows access to these unenveloped nucleocapsids to one of two pathways: egress through the cell body or transport into the axon.     

Cytochemical characterization of tegument membrane-associated carbohydrates in Taenia crassiceps larvae.

The tegument of larval Taenia crassiceps possesses a surface coat rich in both neutral and acidic carbohydrates. Neutral glycans were detected in Golgi vesicles of the tegument perikarya, vesicles of the distal tegument, and on the surface of the plasma membrane. Autoradiographs indicated the tegument perikarya as major sites of 3H-galactose incorporation into acid-insoluble macromolecules. The labeled material is subsequently translocated to more superficial regions of the tegument, then concentrated in the brush border. Loss of radioactivity is appreciable within 6 hr of the synthesis of this material, indicating continual replacement of this tegument surface component.     

Integument of the tapeworm scolex. 1. Freeze-fracture of the syncytial layer, microvilli and discoid bodies

The tegument of cestodes is the most important and structurally complex metabolic interface between these parasites and the hostile environment in which they reside. In spite of the complex metabolic, regulatory and immunological properties of this layer of syncytial cytoplasm, which are relatively well known, the detailed fine structural anatomy of the cestode tegument remains equivocal. The present study therefore reports the freeze-fracture morphology of the tapeworm (Hymenolepis diminuta) tegument. The most important features revealed by analysis of platinum replicas of freeze-fractured tapeworm scolex-neck tegument include: (a) presence of highly ordered linear and/or circumferentially-orientated rows of intramembrane particles situated on the PF fracture face of microvillar plasma membrane, which may participate in movements of the microvilli, (b) presence of apparent 'pores' (11 nm in diameter) at the tips of the tegumentary microvilli, which could serve as regulated gates through which extramicrovillar surface coating materials can be extruded, and (c) the alignment of cytoplasmic discoid bodies into positions at the bases of the surface microvilli such that they could move into the core of each microvillus and thereby release their contents for extrusion (via the pores) onto the outer surface of the microvilli. Concomitantly, the limiting membrane of the discoid bodies could be added to the tegument plasma membrane and thereby contribute to the rapid turnover of the tegumentary surface. This study provides the first detailed account of the ultrastructural anatomy of the tapeworm tegument and is intended to serve as a point of reference for future investigations of tapeworm tegumentary functions.     

扩张莫尼茨绦虫(圆叶目:裸头科)节间腺的超微结构及组织化学

用光学显微镜和透射电子显微镜观察了扩张莫尼茨绦虫节间腺形成过程的精细结构及一些组化变化。结果表明：节间腺是扩张莫尼茨绦虫皮层的特化部分,由节片后缘的皮层及其邻近细胞体向绦虫实质组织中陷入开始其形成过程,随着虫体发育的进行,新的陷入不断形成,原陷入的部分不断脱离皮层形成簇状腺体结构。节间腺的数目随着体节的发育不断增加,幼节中仅有少数几个(6～9个),而远端的孕节中多于100个。电镜下可见腺细胞体由细胞质管与腺皮层相联,簇状腺体结构为一合胞体形态,腺细胞体围绕并开口于椭球体或不规则形状的皮层腔中。离腺皮层远的腺细胞体电子密度高并含有与腺皮层相应的典型分泌颗粒,而靠近腺皮层的腺细胞体电子密度低,所含分泌颗粒较少。扩张莫尼茨绦虫节间腺的组化性质尚不完全清楚。糖与蛋白质等组化结果不稳定,随染液pH值及染色时间的变化等多种因素而改变。基于我们的研究及其他研究者的观察表明,节间腺可能参与外源基质形成虫卵的转运,同时他们可能在虫体节片脱落及虫卵溢出时起作用。     

Ultrastructure of the Tegumental Basement Membrane of Fasciola hepatica(Trematoda)

The fine–structural characteristics of the basement membrane of the tegument of F. hepatica were examined following extraction fixations and tannic acid infiltration. The basement membrane was shown to consist of three layers: lamina lucida, lamina densa, and lamina reticularis. The lamina densa appeared amorphous and homogeneous with tannic acid impregnation. The lamina reticularis appeared as a dense network of 10–12 nm fibrils. Anchoring fibrils cross this layer and form loops. Along their length they contact hemidesmosomes of muscles, thus connecting muscle to muscle and to tegument. The tegument/basement membrane contact is enhanced by extensions of the lamina densa into infoldings of the tegumental basal membrane. Where tegumental spines reach the basement membrane, the contact is reinforced by hemidesmosomes that connect to anchoring fibrils reaching toward the underlying muscles. The basement membrane thus seems to be a complex structure integrating the distal tegumental layer with underlying tissues and transducing muscle contractions to the tegument and its spines.     

Heterogeneity of a fluorescent tegument component in single pseudorabies virus virions and enveloped axonal assemblies

The molecular mechanisms responsible for long-distance, directional spread of alphaherpesvirus infections via axons of infected neurons are poorly understood. We describe the use of red and green fluorescent protein (GFP) fusions to capsid and tegument components, respectively, to visualize purified, single extracellular virions and axonal assemblies after pseudorabies virus (PRV) infection of cultured neurons. We observed heterogeneity in GFP fluorescence when GFP was fused to the tegument component VP22 in both single extracellular virions and discrete puncta in infected axons. This heterogeneity was observed in the presence or absence of a capsid structure detected by a fusion of monomeric red fluorescent protein to VP26. The similarity of the heterogeneous distribution of these fluorescent protein fusions in both purified virions and in axons suggested that tegument-capsid assembly and axonal targeting of viral components are linked. One possibility was that the assembly of extracellular and axonal particles containing the dually fluorescent fusion proteins occurred by the same process in the cell body. We tested this hypothesis by treating infected cultured neurons with brefeldin A, a potent inhibitor of herpesvirus maturation and secretion. Brefeldin A treatment disrupted the neuronal secretory pathway, affected fluorescent capsid and tegument transport in the cell body, and blocked subsequent entry into axons of capsid and tegument proteins. Electron microscopy demonstrated that in the absence of brefeldin A treatment, enveloped capsids entered axons, but in the presence of the inhibitor, unenveloped capsids accumulated in the cell body. These results support an assembly process in which PRV capsids acquire a membrane in the cell body prior to axonal entry and subsequent transport.     

Electron microscopy of the separated outer tegument of the sparganum and its antigenicity

The author reported previously on separation of the outer tegument of the spargana (plerocercoids of Spirometra mansoni) using high concentration of urea solution. To determine which layer of the tegument is separated by this method, an electron microscopic analysis has been processed in this study. It was confirmed that the basement layer of the tegument is separated from the parenchyme of the sparganum. In addition, the antigenicity of the separated outer tegument against the human sparganosis patient sera was evaluated. Numerous antigenic proteins, including 16 and 55 kDa proteins, were noticed in the separated tegument; however, there were no diagnostic 31/36 kDa molecules in this tegument. The molecules reactive with the patient sera in the tegument are to be characterized in future studies.     

Schistocephalus solidus: pinocytosis by the plerocercoid tegument

The possibility of pinocytosis occurring in the tegument of the plerocercoid of Schistocephalus solidus has been investigated by morphological and experimental methods. Electronmicroscopic study showed that the outer syncytial tegument contained numerous electronlucid vesicles. These vesicles had two gradients, the number of vesicles decreasing from the outer canopy region to the inner canopy and from the apical to the basal plasma membrane for any particular region of tegument. A variety of morphological modifications of the apical plasma membrane very similar to those which have been accepted as evidence of pinocytosis in other tissues were present. In vitro studies using horseradish peroxidase, ruthenium red, and lanthanum nitrate showed that all three tracers are taken up by the tegument into membrane-limited vesicles. Vesicles which contained ruthenium red occurred at the base of the tegument within a 5-min incubation period, and their contents appeared to be released into the underlying interstitial material by exocytosis.     

Regional specializations of the tegument of the metacercaria of Timoniella imbutiforme

The ultrastructure of the spinous body tegument of the metacercaria of Timoniella imbutiforme (Molin, 1859) has recently been described. Other regions of the metacercarial tegument, including those of the oral sucker, pharynx, and nephridiopore, demonstrate considerable specializations. The oral sucker tegument had an aspinous outer syncytial layer that possessed a pimpled apical surface as well as enclosing two types of secretory bodies. The pharyngeal tegument likewise lacked spines, but possessed only one type of secretory body, and a smooth but folded outer surface. The nephridiopore tegument, however, showed the greatest degree of specialization possessing a single type of secretory body specific only to this region of the tegument. Also associated with the syncytium here was a prominent long filamentous glycocalyx, and microtubules which were observed for the first time in this region of the tegument.     

Schistosoma mansoni: changes in the outer membrane of the tegument during development from cercaria to adult worm

Hockley D. J. and McLaren D. J. 1973. Schistosoma mansoni: changes in the outer membrane of the tegument during development from cercaria to adult worm. International Journal for Parasitology3: 13–25. The tegumental outer membrane of the cercaria is trilaminate: the adult worm, however, has a seven-layered membrane. Formation of the heptalaminate membrane commences immediately after the cercaria has penetrated the vertebrate host: multilaminate membrane-bounded vacuoles are passed from subtegumental cells into the tegument where they enlarge, join to the outer membrane and open to the exterior. The heptalaminate limiting membrane of the vacuole thus becomes the outer membrane of the tegument. At the same time the original trilaminate tegumental membrane is formed into microvilli which are cast off and thus the cercarial outer membrane is lost. Schistosomula usually have a heptalaminate outer membrane within three hours of penetration. After this time the large vacuoles are replaced by smaller membraneous bodies which presumably contribute to the outer membrane during growth of the schistosomulum. The membraneous bodies are also present in the tegument of the adult worms and there is some evidence that the outer membrane is continually renewed.     

Tegument Proteins of Human Cytomegalovirus

Human cytomegalovirus (HCMV) is a common, medically relevant human herpesvirus. The tegument layer of herpesvirus virions lies between the genome-containing capsids and the viral envelope. Proteins within the tegument layer of herpesviruses are released into the cell upon entry when the viral envelope fuses with the cell membrane. These proteins are fully formed and active and control viral entry, gene expression, and immune evasion. Most tegument proteins accumulate to high levels during later stages of infection, when they direct the assembly and egress of progeny virions. Thus, viral tegument proteins play critical roles at the very earliest and very last steps of the HCMV lytic replication cycle. This review summarizes HCMV tegument composition and structure as well as the known and speculated functions of viral tegument proteins. Important directions for future investigation and the challenges that lie ahead are identified and discussed.     

Ultrastructural and histochemical observations on the tegument of Gastrodiscoides hominis (Paramphistoma: Digenea)

The tegument of the paramphistome, Gastrodiscoides hominis, is basically similar to that of other digeneans. It is folded into concentrically arranged furrows and ridges bearing numerous tightly packed tubercules, and extends into the oral cavity. An area of specialized tegument is present on the ventral surface, anterior to the disc region. Mitochondria are absent from the tegumental syncytium and underlying tegumental cells, suggesting that the tegument may serve principally as a protective layer rather than in active uptake phenomena. However, extensions of the lymph and parenchyma systems are closely associated with the base of the tegumental syncytium and may provide ATP for active processes. Ciliated and non-ciliated sensory papillae are present, particularly around the oral opening. Numerous lymph channels are present in the sub-tegument and may be involved in osmoregulation.     

The ultrastructural architecture of the adult Schistosoma japonicum tegument

The tegument of the adult blood fluke Schistosoma japonicum is in direct contact with the host blood and immune systems. A comprehensive understanding of the ultrastructure of the tegument is crucial to the understanding of how the parasite maintains itself within the mammalian host. Important functions such as nutritional uptake and immune evasion are suspected functions of the tegument and this review discusses these aspects and presents some insights into some of these crucial functions. Transmission electron microscopy has allowed the identification of ultrastructural features of the adult S. japonicum, some of which differ from the reported features of other schistosome species. Morphological differences within the tegument of the adult S. japonicum are noted between sexes, among different regions of the worms and between aspects along the length of the parasite. Differences included variations in the ultrastructure, size and number of tegumental bodies and mitochondria within the matrix, and differences in the relative area of the apical surface of the tegument. Functions of the various components of the tegument matrix and specialised functions of different regions of the male and female parasites are discussed based on ultrastructural findings and previously reported biochemical and molecular data.