Vitellogenesis in the cestode Atractolytocestus huronensis Anthony, 1958 (Caryophyllidea: Lytocestidae)

Molecular cytogenetic analysis of a triploid population of the human broad tapeworm, Dibothriocephalus latus (Diphyllobothriidea)

The large-sized tapeworm Dibothriocephalus latus is known as the broad or fish-borne cestode of mammals that is capable to infect humans and cause diphyllobothriosis. Recently, molecular data on D. latus has been accumulating in the literature and a complete genome sequence has been published; however, little is known about the karyotype and chromosome architecture. In this study, an in-depth karyological analysis of 2 D. latus specimens was carried out. The plerocercoids originated from a perch caught in subalpine Lake Iseo (Italy) and the tapeworms were reared in hamsters. Both specimens contained cells with a highly variable number of chromosomes ranging from18 to 27. Nevertheless, the largest portion of mitotic figures (47%) showed a number corresponding to the triploid set, 3n = 27. Accordingly, the karyotype of the analyzed specimens consisted of 9 triplets of metacentric chromosomes. Fluorescence in situ hybridization (FISH) with the 18S rDNA probe clearly demonstrated the presence of 3 clusters of hybridization signals on the triplet of chromosome 7, thus confirming the triploid status of the specimens. FISH with a telomeric (TTAGGG)n probe confined hybridization signals exclusively to the terminal chromosomal regions, supporting the earlier findings that this repetitive motif is a conserved feature of tapeworm telomeres.

Functional ultrastructure and cytochemistry of vitellogenesis and mature vitellocytes of the digenean Cainocreadium labracis (Dujardin, 1845), parasite of Dicentrarchus labrax (L., 1758)

Vitellogenesis and vitellocytes of Cainocreadium labracis were studied by transmission electron microscopy (TEM) and TEM cytochemistry. Four developmental stages were distinguished during vitellogenesis: (I) stem cell of high nucleo-cytoplasmic ratio; (II) early differentiation with chief activity focused on the beginning of protein synthesis and shell globule formation; (III) advanced differentiation with rapid intensification of protein synthesis, progressive fusion of single shell globules into large globule clusters, and formation of unsaturated lipid droplets surrounded by β-glycogen particles; and (IV) mature vitellocyte. Early vitellogenesis with vitellocyte maturation consists of: (1) increase in cell volume; (2) increased development of large, parallel cisternae of GER with production of proteinaceous granules; (3) development of small Golgi complexes that package granules; and (4) within vacuoles, progressive enlargement of proteinaceous granules into shell globule clusters formed during vitellogenesis. Three types of inclusions accumulate in large amounts in mature vitelline cells: (1) shell globule clusters, important component in the formation of egg shell; (2) numerous unsaturated lipid droplets. Though fewer, there are also diphasic droplets consisting of saturated and unsaturated lipids in the same droplet, and (3) a relatively small amount of β-glycogen particles, usually surround a few groups of lipid droplets. The β-glycogen and lipid droplets are nutritive reserves for embryogenesis. General pattern and functional ultrastructure of vitellogenesis greatly resemble those observed in some lower cestodes, such as bothriocephalideans and diphyllobothrideans. Variations and differences in the amount of lipids and of glycogen during vitellogenesis in lower cestodes and other trematodes are compared and discussed.

Vitellogenesis of diphyllobothriidean cestodes (Platyhelminthes)

The recently erected cestode order Diphyllobothriidea is unique among all tapeworm orders in that its species infect all major groups of tetrapods, including man. In the present paper, the vitellogenesis of representatives of all three currently recognized families of this order was evaluated, based on ultrastructural (transmission electron microscopy) and cytochemical (detection of glycogen) observations. Vitelline follicles of all taxa studied, i.e. Cephalochlamys namaquensis from clawed frogs (Xenopus), Duthiersia expansa from monitors (Varanus) and Schistocephalus solidus that matures in fish-eating birds, contain vitelline cells at various stages of development and interstitial cells. Developing vitellocytes are characterized by the presence of mitochondria, granular endoplasmic reticulum and Golgi complexes involved in the synthesis of shell globules and formation of shell globule clusters. Mature vitellocytes contain lipids and glycogen in different proportions. The most significant differences among the three diphyllobothriidean families were found in the presence or absence of lamellar bodies. Variations of vitelline clusters morphology and types of lipid droplets are described and discussed in relation to the presumed evolutionary history of diphyllobothriideans, which belong to the most basal cestode groups.

First study of vitellogenesis of the broad fish tapeworm Diphyllobothrium latum (Cestoda, Diphyllobothriidea), a human parasite with extreme fecundity

In the present study, the process of vitellogenesis of one of the most prolific organisms, the broad tapeworm, Diphyllobothrium latum, the causative agent of human diphyllobothriosis, was studied for the first time using transmission electron microscopy. Cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for detection of glycogen was applied. Starting from the periphery toward the center of the vitelline follicle four stages of vitellocytes are differentiated: immature vitellocytes, early maturing vitellocytes, advanced maturing and mature vitellocytes. Differentiation into mature vitellocytes involves the formation of shell globule clusters containing shell globules, large amount of saturated lipid droplets and glycogen. A peculiar ultrastructural feature of D. latum vitellogenesis is the presence of lamellar bodies in the cytoplasm of mature vitellocytes. This feature is similar to that present in the closely related caryophyllideans and spathebothriideans. Despite the great similarity observed in the embryonic development of diphylobothriideans, caryophyllideans and spathebothriideans, and the fact that their vitellocytes share a feature not reported from other cestode groups, there are substantial differences in the morphology of vitelline clusters, types, amount and localization of their nutritive reserves.

Cytocomposition of the vitellarium in Khawia sinensis Hsü, 1935 (Cestoda, Caryophyllidea, Lytocestidae): another caryophyllidean species with lamellar bodies and lipids

The vitellarium of the invasive caryophyllidean tapeworm Khawia sinensis Hsü, 1935 from carp Cyprinus carpio L. was examined by means of transmission electron microscopy and cytochemical staining for glycogen with periodic acid-thiosemicarbazide-silver proteinate (PA-TSC-SP). A vitellarium consists of numerous follicles of irregular size that are interconnected by a net of vitelline ducts. Vitelline follicles are composed of vitelline cells at various stages of development that are interconnected by interstitial tissue. Vitelline follicles are surrounded by a cytoplasmic sheath associated with an intercellular matrix. Extensive development of the granular endoplasmic reticulum and Golgi complexes are both involved in the production of shell globules/shell globule clusters and characterise cytodifferentiation of vitellocytes. Nuclear and nucleolar transformation lead to the formation and storage of intranuclear glycogen, a feature specific for the Caryophyllidea. Newly observed within the mature vitellocytes of Khawia sp. is the presence of lamellar bodies and a few lipid droplets. These cytoplasmic inclusions first occur in the mature cells within the follicles and persist in the vitelline cells within vitelloducts and intrauterine eggs. Two types of lamellar bodies are detected: regular lamellar-structured body and irregular lamellar-structured body. None of the lamellar bodies are membrane bound. Results of the present study indicate that the formation of lamellar bodies may be closely related to the endoplasmic reticulum or shell globule clusters. Some of the shell globule clusters are transformed into lamellar body clusters. Ultrastructural features of vitellocytes in K. sinensis are compared with those of other monopleuroid, polypleuroid, and strobilated cestodes.

Fine structure of the uteri in two hymenolepidid tapeworm Skrjabinacanthus diplocoronatus and Urocystis prolifer (Cestoda: Cyclophyllidea) parasitic in shrews that display different fecundity of the strobilae

Adult specimens of Skrjabinacanthus diplocoronatus and Urocystis prolifer were investigated by light and transmission electron microscopy, and data on the uterine organization in these species are presented. The interrelationships of morphological changes of the uterus and developing eggs on the one hand with fecundities of the strobilae of cyclophyllidean cestodes on the other hand are investigated. The development of the excretory system forming a network of excretory ducts close to the uterus is characteristic of S. diplocoronatus. Numerous excretory ducts are located near the uterus or contact the uterine epithelium and are also found in uterine cords. Accumulation of lipids is observed in the cavity of excretory ducts, in muscular cells, and in the lumen of the uterus as well as in the developing eggs. This species displays the largest fecundity among cestode parasites of the shrew. U. prolifer has one of the lowest fecundities among cestodes from shrews. A small amount of lipids found in cells of gravid proglottids could serve as a supply of nutrients. It seems that some cestodes with great fecundity possess specific paths by which eggs are supplied with nutrients. As a result, diverse modifications of the uterus in Cyclophyllidea are formed.

Early intrauterine embryonic development in Khawia sinensis Hsü, 1935 (Cestoda, Caryophyllidea, Lytocestidae), an invasive tapeworm of carp (Cyprinus carpio): an ultrastructural study

Intrauterine embryonic development in the caryophyllidean tapeworm Khawia sinensis has been investigated using transmission electron microscopy and cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for glycogen. Contrary to previous light microscopy findings that reported the release of non-embryonated eggs of K. sinenesis to the external environment, the present study documents various stages of embryonation (ovoviviparity) within the intrauterine eggs of this cestode. At the initial stage of embryonic development, each fertilised oocyte is accompanied by several vitellocytes that become enclosed within the operculate, electrondense shell. Cleavage divisions result in formation of blastomeres (up to about 24 cells) of various sizes. Mitotic divisions and apparent rosette arrangment of the blastomeres, the latter atypical within the Eucestoda, are observed for the first time in the intrauterine eggs of K. sinenesis. The early embryo enclosed within the electrondense shell is surrounded by a thin membraneous layer which in some enlarged regions shows presence of nuclei. Simultaneously to multiplication and differentiation, some of the blastomeres undergo deterioration. A progressive degeneration of the vitellocytes within eggs provides nutritive reserves, including lipids, for the developing embryo. The possible significance of this atypical timing of the intrauterine embryonic development to (1) the ecology of K. sinensis and that of a recent introduction of another invasive tapeworm, the caryophyllidean Atractolytocestus huronensis Anthony, 1958 to Europe; and (2) the affiliation of caryophyllideans with other lower cestodes, are discussed.

Ultrastructural study of vitellogenesis in Maritrema feliui (Digenea, Microphallidae)

During vitellogenesis in the microphallid trematode Maritrema feliui, we distinguished four stages: (I) a stem cell stage of the gonial type; (II) an early differentiation stage with the main cell activity concentrated on the initiation of protein synthetic activity and the beginning of shell globule formation; (III) an advanced differentiation stage concentrated on a rapid intensification of protein synthetic activity, the progressive fusion of individual shell globules into large shell globule clusters and the formation of saturated lipid droplets and a small amount of β-glycogen particles in the peripheral cytoplasm, considered as a store of nutritive reserves for the developing embryos; and (IV) the mature vitellocyte. Early vitellocyte maturation is characterised by: (1) an increase in cell volume; (2) extensive development of large, labyrinth-like cisternae of GER that produce proteinaceous granules; (3) the development of Golgi complexes engaged in packaging this material; and (4) a continuous enlargement of proteinaceous granules within vacuoles and their transformation into shell globule clusters composed of the heterogeneous material observed during vitellocyte cytodifferentiation. Mature vitelline cells are very rich in two types of cell inclusions accumulated in large amounts in their cytoplasm: (1) shell globule clusters, which play an important role in eggshell formation; and (2) a few osmiophobic lipid droplets of a saturated nature that undoubtedly represent nutritive reserves for the developing embryos. In addition, there are small numbers of β-glycogen particles in the peripheral cytoplasm of mature vitellocytes of this species. The general pattern and ultrastructure of vitellogenesis in M. feliui greatly resembles those observed in another microphallid trematode, Maritrema linguilla, in other digeneans and in some lower cestodes. Quantitative and qualitative variations in lipids (saturated and unsaturated) and glycogen (α-glycogen rosettes and β-glycogen particles) during platyhelminth vitellogenesis between the different species of trematodes and some lower cestodes are identified and discussed.

Ultrastructural and cytochemical studies of GER-bodies in the intrauterine eggs of Wenyonia virilis Woodland, 1923 (Cestoda, Caryophyllidea)

Ultrastructural and cytochemical characteristics of GER-bodies observed in the vitellocyte cytoplasm of the intrauterine eggs of the caryophyllidean cestode Wenyonia virilis are described. In this species GER-bodies were observed only in the cytoplasm of vitellocytes, surrounded by a newly formed egg-shell. They are composed of spherical areas of condensed, electron-dense cytoplasm which contains concentrically arranged parallel lamellae of granular endoplasmic reticulum (GER), forming characteristic balls of different sizes. Each GER-body is surrounded by numerous free ribosomes, polyribosomes, α-glycogen rosettes and large mitochondria. Results of cytochemical analysis by means of PATSC-SP test for polysaccharides indicated that glycogen is absent within the GER-bodies, however, a strongly positive reaction was observed only in large aggregations of α-glycogen rosettes and β-glycogen particles, localised usually near GER-bodies.

Ultrastructural aspects of spermatogenesis, testes, and vas deferens in the parthenogenetic tapeworm Atractolytocestus huronensis Anthony, 1958 (Cestoda: Caryophyllidea), a carp parasite from Slovakia

Spermatogenesis, testes, and vas deferens in the parthenogenetic monozoic tapeworm Atractolytocestus huronensis Anthony, 1958 (Cestoda: Caryophyllidea) from Slovakia, parasitizing the carp Cyprinus carpio L., have been investigated by means of transmission electron microscopy for the first time. The present results show that helminths with parthenogenetic and normal reproduction may share some common spermatology features, e.g., dense cytoplasm of the peripherally localized spermatogonia or a rosette type of spermatogenesis. In contrast to tapeworms with normal reproduction, the most prominent ultrastructural characteristic of the spermatocytes of A. huronensis is fragmentation of their nuclei. This clear feature of cell degeneration might be a consequence of the aberrant first meiotic division. Peripheral cortical microtubules and a single centriole, indicators of the ongoing spermiogenesis, were observed only very rarely in the early spermatids. Characteristics of normal spermiogenesis, i.e., apical dense material in the zone of differentiation in early stages of spermiogenesis, flagellar rotation, and proximo-distal fusion, were never found in the present study. The testes follicles are surrounded by a thin cytoplasmic sheath underlined by a basal lamina. Vas deferens is lined by flat epithelium with numerous surface lamellae and cilia. Mature, functional spermatozoa were not observed in the vas deferens of A. huronensis from Slovakia.