The Fine Structure of Secretion in Hyalophysa chattoni: Formation of the Attachment Peduncle and the Chitinous Phoretic Cyst Wall

ABSTRACT. The settling tomite stage of the apostome Hyalophysa chattoni secretes a phoretic cyst wall composed of chitin, mucopolysaccharides, and protein. Within 1 1/2 h after settling, an electron-dense proteinaceous cyst layer (the outer layer) is formed from secretions originating at the base of the kineties and from the thick pellicular layer between the kineties. The inner cyst layer, composed primarily of chitin (acidic and neutral polysaccharides are also present), is secreted across the entire cell surface. Cyst wall formation is completed within 6 h. The fine structure of endocyst secretion resembles stages in the secretion of chitin by fungi, yeasts, and arthropods. A proteinaceous attachment peduncle is secreted to anchor the cell to a shrimp host and is formed by the release of electron-dense secretory bodies from the cell's ventral surface.     

Light and transmission electron microscopical studies and amino acid analysis of the metacercarial cyst of Zygocotyle lunata (Trematoda).

Light microscopical studies indicated that the cyst of Zygocotyle lunata consists of outer, inner and ventral cyst walls. Transmission electron microscopical studies showed that the outer cyst and the ventral cyst each consist of two layers. The inner cyst is lamellated and contains a specialized ventral region designated the ventral lid. Amino acid analysis of cyst walls showed only trace amounts of cysteine, indicating that disulphide bonds are not used to stabilize the inner cyst of Z. lunata.     

A histochemical study of the secretory gland cells of Cercaria shikokuensis and their role during development from cercaria to metacercaria.

The roles of secretory glands during the developmental process from an immature cercaria to a metacercaria in Cercaria shikokuensis were studied. Four types of secretory cells were identified in this species. On maturation of the cercaria in redia, the products of ventral gland cells and mucoid gland cells formed a thick surface coat on the mature cercaria, and the products of cephalic gland cells also formed a thin cover on the surface coat. In the process leading to the formation of a metacercaria, the surface coat constituted the outer layer of the cyst, mucoid gland cells secreted mucous substances inside the wall, and then cystogenous gland cells discharged their products to the inner wall. The cyst wall was composed of four layers, and it was thought that the outermost surface layer helped the cyst wall to adhere to the matrix and the intermediate layers helped to put together outer and inner walls.     

Histochemical and ultrastructural studies on the metacercarial cyst of Echinostoma revolutum (Trematoda).

Histochemical and ultrastructural studies were made on the metacercarial cyst of Echinostoma revolutum obtained from the kidney of experimentally infected Physa and Lymnaea snails. Ultrastructural studies revealed three cyst walls, an outer, middle and inner. The outer wall was more electron-dense than the middle, and contained coarser granules than those found in the middle layer. The inner wall was lamellated and contained membranous whorls. Collagenous fibers presumably of host origin surrounded the outer cyst wall. The outer and middle cyst walls stained identically with all histochemical procedures used. These walls contained acid mucopolysaccharides and glycoprotein, whereas the inner cyst wall contained glycoprotein. All cyst walls stained positively with a variety of protein stains.     

The fine structure of secretion in Hyalophysa chattoni: formation of the attachment peduncle and the chitinous phoretic cyst wall.

The settling tomite stage of the apostome Hyalophysa chattoni secretes a phoretic cyst wall composed of chitin, mucopolysaccharides, and protein. Within 1 1/2 h after settling, an electron-dense proteinaceous cyst layer (the outer layer) is formed from secretions originating at the base of the kineties and from the thick pellicular layer between the kineties. The inner cyst layer, composed primarily of chitin (acidic and neutral polysaccharides are also present), is secreted across the entire cell surface. Cyst wall formation is completed within 6 h. The fine structure of endocyst secretion resembles stages in the secretion of chitin by fungi, yeasts, and arthropods. A proteinaceous attachment peduncle is secreted to anchor the cell to a shrimp host and is formed by the release of electrondense dense secretory bodies from the cell's ventral surface.     

The role of the follicle cells during oogenesis in the chiton Sypharochiton septentriones (Ashby) (Polyplacaphora,Mollusca)

Summary Histochemical studies and electron microscopic investigations on the role of the follicle cells during oogenesis in the chiton Sypharochiton septentriones showed that the main role of the follicle cells was the deposition of a spiny chorion around each oocyte. The chorion was composed of three layers; an inner, acid mucopolysaccharide layer, which was a primary egg membrane secreted by Golgi bodies in the cortical cytoplasm of the oocyte, an intermediate layer of protein and an outer layer of lipid. The intermediate and outer layers were secreted by the follicle cells and were thus secondary egg membranes.     

The histochemistry of Stellantchasmus falcatus Onji and Nishio, 1915 (Trematoda: Heterophyidae) metacercarial cyst in the mullet Mugil cephalus L. and histopathological alterations in the host†

The metacercarial cyst of the heterophyid trematode Stellantchasmus falcatus in the striated muscles of the mullet Mugil cephalus consists of three layers. Histochemical studies have indicated that these layers are chemically distinct. The acellular inner layer is comprised of complex carbohydrate polyanions rich in acidic groups while the medial cellular layer is comprised of a neutral mucopolysaccharide including a moeity of carbohydrate poiyanions. These two layers are believed to be of parasite origin. The outer layer is cellular and is of host origin. It is the most chemically complex and is believed to include one or more of the following: mucopolysaccharides, glycolipids and phospholipids. In addition, the carbohydrate moeity associated with the mucopolysaccharides and/or glycolipids is in the form of sulphated carbohydrate polyanions with undissociated carboxyls as well as acidic groups. The presence of the parasite results in the necrotic degeneration of the host's myofibers situated in the proximity of the parasite. Large fat cells fill the spaces vacated by necrotic muscle cells and many blood cells occur along the periphery of the parasite.     

Histochemistry and ultrastructure of the metacercarial cysts of blackspot trematodes Uvulifer ambloplitis and Neascus pyriformis

Cysts of Uvulifer ambloplitis from green sunfish, Lepomis cyanellus, and Neascus pyriformis from red shiners, Notropis lutrensis, were studied with light-level histochemistry and scanning and transmission electron microscopy. Cysts of both species are bilayered, consisting of an outer host capsule and an inner parasite cyst; the space between these layers is filled with a viscous material. The outer portion of the host capsule of both species is composed of fibrocytes, melanin granules, and collagen fibrils, and the inner portion of layers of flattened fibrocytes. The parasite cyst of U. ambloplitis is formed of 2 layers, an outer dense layer and an inner light layer, whereas the parasite cyst of N. pyriformis is made of 3 layers. A thin outer light-staining layer is present in addition to the 2 layers observed in U. ambloplitis. Results of histochemical staining were the same for both species. The host capsule stained positively for proteins and neutral and acid mucopolysaccharides. The viscous material was positive for neutral and acid mucopolysaccharides but not for proteins. The parasite cyst gave a strong positive reaction for neutral mucopolysaccharides but was negative for acid mucopolysaccharides and proteins.     

Freeze-Etching of Azotobacter vinelandii: Examination of Wall, Exine, and Vesicles

The structure of the cell wall, the arrangement of the cyst exine, and the origin and distribution of intine vesicles in Azotobacter vinelandii ATCC 12837 were examined by freeze-etching and conventional electron microscopic techniques. In the vegetative organism the cell wall appears to have a woven texture which disappears during cyst formation. The exine is composed of two different types of material: the outer layer is a fibrous, amorphous layer, and the numerous inner layers form the basic hexagonal structures which unite to form the cyst coat. The presence of intine vesicles in the encysting organism was confirmed in frozen-etched cells. The appearance of frozen-etched cells and cysts and the distribution of capsular material indicate that extracellular polysaccharide is an important factor in cyst formation.     

The formation of the cyst wall of the metacercaria of Fasciola hepatica L.

Summary The several concentric layers of the cyst wall of Fasciola hepatica are formed from precursors synthesised in the cystogenic cells of the cercaria during its development in the redia. A cinematographic analysis shows that the separate components are released in succession during encystment.The outer portion of the wall consists of two layers: a tanned protein and a carbohydrate-protein complex. The granular precursors of these are formed in separate groups of cells and migrate from these cells into the superficial epithelium (embryonic epithelium) during development. They are released to form the outer wall by the bursting of the embryonic epithelium at the beginning of encystment. This process is rapid and is completed in a few minutes.A pause follows the separation of the outer wall during which a further polysaccharide layer is released and the cells, which contain the rod-like scrolls of sheets of the laminated component of the inner wall, migrate from within the cercaria through gaps in the superficial musculature on to the cercarial surface to form a new epithelium replacing that previously shed.The cercaria now begins a series of complex oscillatory movements within the enveloping outer cyst wall during which the scrolls are secreted into the space underneath the outer wall, unroll and are compacted by the animal's movements into the lamellar inner wall.The rodlets are enclosed in vacuoles and their secretion is effected by the fusion of the vacuolar membrane with the plasma membrane without destroying the integrity of the cells, which remain to constitute the epithelium of the juvenile fluke when this emerges later.     

Structure and composition of the metacercarial cyst wall of Sphaeridiotrema globulus (Trematoda)

1986. Structure and composition of the metacercarial cyst wall of Sphaeridiotrema globulus (Trematoda). International Journal for Parasitology 16: 647–653. Histochemical and structural observations were made on the metacercarial cyst wall of Sphaeridiotrema globulus, obtained from naturally infected Goniobasis virginica (Pleuroceridae) snails. The cyst wall of S. globulus is a thin, glistening, transparent structure that thickens as the metacercaria ages. The cysts occur singly beneath the shell of the snail host or linked together in sheets, pyramids and other three dimensional forms. Light and electron microscopic examination of the cyst wall reveals an inner, middle and outer layer, each of which may vary in thickness. Adjacent cysts are linked by their outer layers. The chemical composition of these layers, elucidated through histochemistry, is described.     

Ultrastructural and histochemical studies on the epithelium revestment layer in the tube feet of the starfish Asterina stellifera

The “cuticle,” which revests the starfish tube foot, has been studied by electron microscopy and the findings correlated with histochemical observations. The “cuticle” is composed by two distinct zones; an outer zone including numerous microvilli, which extend from the inner zone into and through a fibrillar substance distinctly organized in two layers. These microvilli protrude slightly beyond the outer surface, where their tips give rise tonumerous extremely delicate fibrils. The second inner zone, of quite variable thickness and condensation of material, presents a coarser fibrous matrix where organelles and inclusions can be found. The whole cuticular complex does not derive from the majority of the epithelial cells, but is probably an extension of a special kind of T-shaped cells appearing at intervals, the “cuticle” forming a syncytial surface. Histochemical investigations indicate that the “cuticle” contains a combination of neutral and acid mucopolysaccharide, with a marked neutral predominance, the outer one displaying also an extremely thin coat of acid mucopolysaccharide with the sulfate group. The ordered arrangement of the microvilli suggests that this situation is imposed by the strong bond existing between the microvilli and the ouble mucopolysaccharide layers which would act as a cementing substance stabilizing the entire apical surface of the cell.     

The fine structure of the phoront of Gymnodinioides pacifica, a ciliated protozoan (Ciliophora, Apostomatida) from euphausiids of the Northeastern Pacific

Phoretic stages of the exuviotrophic apostome Gymnodinioides pacifica were examined using transmission and scanning electron microscopy (TEM and SEM). TEM revealed that the mature cyst wall possesses 2 or 3 layers differing by the presence or absence of the third inner layer. This inner layer may represent a different form of the middle wall material. The inner cyst layer is approximately 0.15 microm thick and has striations with a periodicity of approximately 19 nm. The middle cyst layer has a variable thickness and the outer dense layer is approximately 0.1 microm thick. The 3 layered cyst wall had a thickness of 0.3-0.7 microm and averaged 0.5 microm. Advanced phoront stages were enclosed by fully formed cyst walls or by cyst walls thinned to approximately 0.1 microm, as the phoronts prepared to excyst prior to host ecdysis. Additionally, we report the fine structure of the rosette, trichocysts, nuclei, food plaquettes, oral fiber, and other cytoplasmic inclusions. SEM revealed an outer cyst wall layer connected to the secreted peduncle material, which was observed to extend over a wide (15 microm) area on the host setae. Cysts were usually attached at their posterior ends or, less frequently, along their side.     

腔阔盘吸虫尾蚴及后蚴穿刺腺等腺体的组织化学及其功能的初步研究

本文报道应用组织化学反应方法初步观察了腔阔盘吸虫(Eurytrema coelomaticum)尾蚴及后蚴体中单细胞腺的组织化学成分及其生理功能。尾蚴的5对大单细胞腺主要分泌粘蛋白、酸性粘多糖及微量碱性蛋白质,当子胞蚴被排到外界时,此腺体物质分泌出充满子胞蚴内囊腔并包被着各尾蚴。尾蚴在此腺体分泌物保护下渡过其在外界生存的时间。尾蚴的4对小单细胞腺主要包含中性糖蛋白及结合氨基的蛋白质(可能是含酶物质),此腺体物质可能是在尾蚴进入昆虫宿主(草螽)体内穿钻其胃壁进入血腔时分泌出能溶解胃壁组织帮助尾蚴的穿钻行为。成熟后蚴的穿刺腺对PAS反应呈强阳性,其分泌物可以溶解囊蚴的囊壁,使后蚴迅速脱囊。各幼虫期其他器官组织的组化成分也经观察。     

The fine structure of the cystogenic cells of the cercaria of Fasciola hepatica L.

Summary The wall of the cyst of the metacercaria of the liver fluke (Fasciola hepatica L). is composed of four layers: an external tanned protein, two layers giving reactions of proteins and polysaccharides and an internal, finely laminated layer of keratinized protein. Each of the precursors of these layers is synthesised in a distinct kind of cystogenic cell in the cercaria, while it is still within the redia in the intermediate host, a snail.The cells forming the protein precursors are similar in cytoplasmic structures to secretory cells such as those of the exocrine pancreas. The cells producing protein and polysaccharides resemble mucinogenic cells.The keratin precursor is a rodlet formed by the rolling of a sheet into a scroll and all stages of this process can be recognised in the synthesising cells in the early cercaria.     

THE FINE STRUCTURE OF ACANTHAMOEBA CASTELLANII (NEFF STRAIN) : II. Encystment

Encysting cells of Acanthamoeba castellanii, Neff strain, have been examined with the electron microscope. The wall structure and cytoplasmic changes during encystment are described. The cyst wall is composed of two major layers: a laminar, fibrous exocyst with a variable amount of matrix material, and an endocyst of fine fibrils in a granular matrix. The two layers are normally separated by a space except where they form opercula in the center of ostioles (exits for excysting amebae). An additional amorphous layer is probably present between the wall and the protoplast in the mature cyst. Early in encystment the Golgi complex is enlarged and contains a densely staining material that appears to contribute to wall formation. Vacuoles containing cytoplasmic debris (autolysosomes) are present in encysting cells and the contents of some of the vacuoles are deposited in the developing cyst wall. Lamellate bodies develop in the mitochondria and appear in the cytoplasm. Several changes are associated with the mitochondrial intracristate granule. The nucleus releases small buds into the cytoplasm, and the nucleolus decreases to less than half its original volume. The cytoplasm increases in electron density and its volume is reduced by about 80%. The water expulsion vesicle is the only cellular compartment without dense content in the mature cyst. The volume fractions of lipid droplets, Golgi complex, mitochondria, digestive vacuoles, and autolysosomes have been determined at different stages of encystment by stereological analysis of electron micrographs. By chemical analyses, dry weight, protein, phospholipid, and glycogen are lower and neutral lipid is higher in the mature cyst than in the trophozoite.     

Anther ontogeny in Campsis radicans (L.) Seem. (Bignoniaceae)

In this study anther ontogeny of Campsis radicans (L.) Seem. was investigated by transmission electron microscopy and light microscopy with special reference to the development of the anther wall. The anther wall formation follows the dicotyledonous type. The differentiation in anther starts with the appearance of archesporial cells which undergo periclinal divisions to give primary parietal layer to the epidermal site and the primary sporogenous cells to the inside. The primary parietal layer also divides to form two secondary parietal layers. Later, the outer secondary parietal layer (spl1) forms the endothecium and the middle layer by periclinal division whereas the inner one (spl2) directly develops into the outer tapetum forming the inner most layer of the anther wall. The sporogenous tissue is generally organized in two rows of cells with a horseshoe-shaped outline. The remainder of the tapetum lining the sporogenous mass is derived from the connective tissue. The tapetum thus has dual origin and dimorphic. Anthers are tetrasporangiate. The wall of the anther consists of an epidermis, endothecium, middle layer, and the secretory type tapetum. Tapetal cells are usually binucleated. Epidermis and Endothecium layers of anther wall remain intact until the end of anther and pollen development; however, middle layer and tapetum disappear during development.     

Stereoscan studies of rediae, cercariae, cysts, excysted metacercariae and migratory stages of Fasciola hepatica

The external surface of the redial body of Fasciola hepatica is provided with microvillus-like projections or short lamellae, and short cilium-like structures are common anteriorly. The anterior part of the cercarial body possesses a pattern of regularly arranged small depressions each containing a spine. Both long and short cilium-like structures occur anteriorly. The tail is spineless and provided with dorsolateral folds. The outer cyst wall is formed by granules secreted from the tegument all over the body apart from the ventral sucker. Most granules transform into fibrillae which form the thick outer spongy layer. The precursor of the inner cyst wall is at the beginning closely attached to the metacercarial surface, but later the membrane-like cyst wall extends, and when fully formed the metacercaria lies free in the flattened circular inner cyst. The ventral plug is formed by the ventral sucker. The tegument of newly excysted metacercariae is provided with simple pointed spines, but later during migration in the mouse the spines become flattened and multipointed. Very young migratory stages may be attached with host cells.     

Musculature of the penial complex: A new criterion in unravelling the phylogeny of Hygrophila (Gastropoda: Pulmonata)

The taxonomy of freshwater pulmonates (Hygrophila) has been in a fluid state warranting the search for new morphological criteria that may show congruence with molecular phylogenetic data. We examined the muscle arrangement in the penial complex (penis and penis sheath) of most major groups of freshwater pulmonates to explore to which extent the copulatory musculature can serve as a source of phylogenetic information for Hygrophila. The penises of Acroloxus lacustris (Acroloxidae), Radix auricularia (Lymnaeidae), and Physella acuta (Physidae) posses inner and outer layers of circular muscles and an intermediate layer of longitudinal muscles. The inner and outer muscle layers in the penis of Biomphalaria glabrata consist of circular muscles, but this species has two intermediate longitudinal layers separated by a lacunar space, which is crossed by radial and transverse fibers. The muscular wall of the penis of Planorbella duryi is composed of transverse and longitudinal fibers, with circular muscles as the outer layer. In Planorbidae, the penial musculature consists of inner and outer layers of longitudinal muscles and an intermediate layer of radial muscles. The penis sheath shows more variation in muscle patterns: its muscular wall has two layers in A. lacustris, P. acuta, and P. duryi, three layers in R. auricularia and Planorbinae and four layers in B. glabrata. To trace the evolution of the penial musculature, we mapped the muscle characters on a molecular phylogeny constructed from the concatenated 18S and mtCOI data set. The most convincing synapomorphies were found for Planorbinae (inner and outer penis layers of longitudinal muscles, three-layered wall of the penis sheath). A larger clade coinciding with Planorbidae is defined by the presence of radial muscles and two longitudinal layers in the penis. The comparative analysis of the penial musculature appears to be a promising tool in unraveling the phylogeny of Hygrophila.     

Ultrastructural Changes During Encystment of Schizopyrenus russelli*

Ultrastructural changes associated with the encystment of Schizopyrenus russelli have been studied by electron microscopy. Before encystment small “black bodies” appear in the cytoplasm and later migrate toward the periphery. The outer cyst wall is secreted at this stage as a thin discontinuous layer which thickens and subsequently becomes continuous. Concomitant with this, the endoplasmic reticulum surrounds the mitochondria. The inner cyst wall later appears as a multilayered structure which presumably is cast off from the plasma membrane. Between the inner and outer layers of the cyst wall, there is a middle, less electron-dense layer wherein extruded cytoplasmic material is found embedded at certain places.