THE CYTOLOGY OF THE NORMAL PARATHYROID GLANDS OF MAN AND VIRGINIA DEER : A Light and Electron Microscopic Study with Morphologic Evidence of Secretory Activity

The normal parathyroids of six humans and a Virginia deer were studied by light and electron microscopy. The parenchyma of the deer parathyroid is composed of uniform chief cells, which contained 100 to 400 mµ electron-opaque, membrane-limited granules, presumed to be secretory granules, in addition to the usual cytoplasmic organelles. Desmosomes are present between adjacent cells, and rare cilia are observed protruding from the chief cells into the intercellular space. The human parathyroids contain chief cells in two phases—active and inactive—as well as oxyphil cells. Active chief cells have a large Golgi apparatus, sparse glycogen, numerous secretory granules, and rare cilia. Inactive chief cells contain a small Golgi apparatus, abundant glycogen, and few secretory granules. Both forms have the usual cytoplasmic organelles and, between adjacent cells, desmosomes. Oxyphil cell cytoplasm is composed of tightly packed mitochondria and glycogen granules, with rare secretory granules. Cells with cytoplasmic characteristics intermediate between chief and oxyphil cells, possibly representing transitional cells, have been observed. Secretory granules of both man and deer are composed of 100 to 200 A particles and short rods, and the granules develop from prosecretory granules in the Golgi region of the cell. The human secretory granules are smaller and more variable in shape than those of the deer. The granules are iron and chrome alum hematoxylin-positive, argyrophilic, and aldehyde fuchsin-positive, permitting light microscopic identification. They are also found in the capillary endothelial cells of the parathyroid and in its surrounding connective tissue. The secretory granules of the parathyroid cells can thus be followed from their formation in the Golgi apparatus almost to their extrusion into the blood stream.     

Ultrastructure of odontogenic cells during enameloid matrix synthesis in tooth buds from an elasmobranch, Raja erinacae

The ultrastructure of the inner dental epithelial cells (IDE) and odontoblasts in elasmobranch (Raja erinacae) tooth buds was investigated by transmission electron microscopy to determine what contribution each cell type makes to the forming enameloid matrix. Row II, early stage, IDE cells contained few organelles associated with protein synthesis, whereas preodontoblasts appeared competent to initiate extracellular matrix production. Row III IDE cells are also devoid of organelles related to secretory protein synthesis, although these IDE cells accumulated large pools of intracellular glycogen. The glycogen appeared to be packaged into vesicles and exocytosed into the lateral extracellular space toward the forming enameloid matrix. Row III odontoblasts had a morphology consistent with an active protein secretory cell. No procollagen granules were present within the odontoblasts, however, nor were many collagen fibers observed in the enameloid matrix. Instead, non-collagenous "giant" fibers having 17.5-nm periodic cross striations were associated with the invaginations of odontoblast cell processes. Giant fibers, which spanned a clear zone adjacent to the odontoblasts, terminated within the enameloid matrix. Smaller 25-nm-wide "unit" fibers emanated from the giant fiber tips to form the bulk of the enameloid matrix. The clear zone, which separated the odontoblasts from the enameloid matrix at early stages, diminished in size at later stages until the odontoblast processes were completely embedded in the enameloid matrix. Nascent enameloid crystallites were observed only after a layer of unmineralized predentin was deposited beneath fully formed enameloid matrix. The results suggest that the major constituent of the enameloid matrix in skates is a non-collagenous protein derived from the odontoblasts. The inner dental epithelial cells appear to contribute large quantities of carbohydrates to the forming enameloid matrix.     

Glycosomes (protein-glycogen complex) in the canine heart. Ultrastructure, histochemistry and changes induced by acidic treatment.

Cardiac conducting fibers were selected from two dogs defined as A and B. The specimens differed in the reaction of their electron dense granules, commonly referred to as glycogen, to the treatment en bloc with uranyl acetate. Material was fixed in glutaraldehyde and OsO4. Blocks were processed either conventionally or immersed in uranyl acetate before dehydration. Sections were examined unsatined, stained with U and/or Pb or with a histochemical technique (PA-TSC-SP) specific for glycogen. Electron dense granules have affinity to Os, U and Pb which suggests ionic reactions specific for protein but improbable for glycogen. Large granules in A turned into pale ghosts and small granules in B disappeared after treatment en bloc with uranyl acetate. PA-TSC-SP in conventional samples showed glycogen particles arranged into aggregates corresponding in size to the electron dense granules. Treatment en bloc slightly affected glycogen aggregates in A and resulted in a formation of large clumps of glycogen particles in B. It was concluded that the electron dense granules represented protein bound to glycogen in the organelles called glycosomes. Acidic action of uranyl acetate removed protein from glycosomes. The degree of this removal depended on the amount of protein present in glycosomes in the moment of fixation.     

Studies on the cytophysiology of the fat body of the American silkmoth

Summary A developmental study at the electron microscopic level was conducted of the fat body cells of Hyalophora cecropia (L.). During the last larval instar the fat body increases in volume and the cells exhibit a well developed rough endoplasmic reticulum and protein bodies of diverse sizes. In the pupal fat body, the protein bodies appear to be enclosed by a double membrane and contain glycogen granules, ribosomes and mitochondrion-like structures. In addition, there are large lipid globules, cytolysomes and rough endoplasmic reticulum. The ultrastructure of the protein bodies suggests the development of large bodies by fusion of smaller protein bodies. Changes in fat body cell ultrastructure were followed during adult development and cytological evidence was obtained for the depletion of protein, glycogen and lipid in the female during this period. The female adult fat body cell contains free ribosomes, protein bodies, many mitochondria, a few lipid globules and glycogen granules. The male moth fat body cells have many mitochondria, a few glycogen granules, essentially no protein bodies, but an abundance of large lipid globules.Studies on the influence of egg maturation on the morphology of the fat body of Hyalophora gloveri (L.) revealed that ovariectomy of pupae yielded adults having more fat body than normal females, and that the fat body cells of the ovariectomized animals contained more glycogen, lipid and protein. Male pupae receiving ovarian implants developed into adults containing eggs and possessed more fat body than normal females but less than normal males. Very few glycogen granules were found in the fat body cells of normal males or males with implanted ovaries.Supported by grant AM-02818 from the National Institutes of Health.We thank Dr. James Oschman for his helpful suggestions and constructive criticisms.     

The electron microscopy of normal human oesophageal epithelium.

Oesophageal biopsies were studied with the electron microscope. Three layers were identified, as in the light microscopy of the oesophageal epithelium: basal, prickle and funtional cell layers. A continuous basement membrane separated the lamina propria from the basal cells. The basal cell membrane carried hemidesmosomes, desmosomes and microvillous processes. Their cytoplasm contained the usual organelles plus free ribosomes and tonofirbrils. Prickle cells contained glycogen rosettes and many tonofilaments, and their cell membrane many microvillous and demosomal processes, in places elaborated into desmosome fields. In both these layers there was a wide intercellular space containing some particulate and membranous debris. The flattened cells of the functional layer had fewer desmosomes and microvilli but abundant glycogen and tonofilaments, and a narrow intercellular space. Membrane coating granules first reaching a maximum in the functional cell layer appeared in the upper prickle cell layer and few persisted into the surface cells. The apical cell membrane of the most superficial cells was thickened and had few small microvillous processes, which were covered with a filamentous "fuzzy" coat. No keratohyaline granules were present. Papillae of lamina propria contained capillaries, some with a fenestrated endothelium.     

A fine-structural analysis of mouse molar odontoblast maturation.

The first mandibular molars of the Swiss albino mice, 1 through 4 days of age, were fixed in glutaraldehyde or Karnovsky's fixative. The tissues were postfixed in OSO4, dehydrated and embedded in Epon. The prepolarizing, polarizing and secretory odontoblasts were described. The prepolarizing cells, located in the vicinity of the cervical loop, were mesenchymal-like in morphology. The cells of the polarizing stage possessed organelles indicative of protein synthesis. The nucleus was located proximally. Aperiodic fibers were evident in the wide basement membrane. The secretory odontoblasts were long, slender, polarized cells closely adjoining one another. Each odontoblast possessed six morphologically discernible regions: (1) an infranuclear region, limited in size and containing few cellular organelles; (2) a nuclear region, housing the oval nucleus and a few associated lamellae of rough endoplasmic reticulum as well as a limited number of mitochondria; (3) a supranuclear rough endoplasmic reticulum region, possessing an abundance of these organelles as well as some mitochondria and secretory vesicles; (4) a Golgi region, occupying the middle third of the cell, housing the elements of an extensive Golgi apparatus which was surrounded by peripherally located profiles of rough endoplasmic reticulum; additionally, this region contained smooth endoplasmic reticulum, mitochondria, numerous secretory granules and vesicles and occasional intracellular collagen fibers; (5) an apical rough endoplasmic reticulum region, containing a rough endoplasmic reticulum component that was less extensive than its supranuclear counterpart; in addition, this region was the one richest in mitochondria and contained a plethora of secretory vesicles and granules; (6) the odontoblastic process, a region mostly void of organelles, containing various secretory products, some of which appeared to be in the process of being released extracellularly into the surrounding dentin matrix.     

Fine structure of the corpuscles of stannius in the toadfish.

The micro-anatomy of the corpuscles of Stannius of the toadfish, Opsanus tau, an aglomerular marine teleost, has been studied by light and electron microscopy. The corpuscles are composed of extensively anastomosed cords of epithelial cells which maintain intimate contact with blood capillaries. Most of the epithelial cells contain acidophilic granules which also show a positive reaction with the periodic acid-Schiff technique and aldehyde fuchsin. On the basis of fine structural criteria, three cell types can be recognized. The granular cells contain abundant quantities of granular endoplasmic reticulum, ribosomes, Golgi apparatus with prosecretory granules, coated vesicles, polymorphic mitochondria with lamellar cristae, filaments, microtubules, a cilium, a variety of lysosome-like dense bodies, glycogen particles, lipid droplets, secretory granules and intranuclear lipid-like inclusions. One variety of agranular cell (type I) is characterized by the total absence of secretory granules, but it contains large amounts of granular endoplasmic reticulum and ribosomes, conspicuous profiles of Golgi apparatus, coated vesicles and sometimes an abundance of glycogen. Another variety of agranular cell (type II) has poorly developed cytoplasmic organelles. The perivascular space between the capillary and parenchyma contains connective tissue cells and abundant nerve fibers. The different types of epithelial cells observed in the corpuscles of Stannius of this fish may represent functional stages of the secretory cycle in a single cell type.     

Internal defenses of the snail Biomphalaria glabrata.

We describe three distinct types of cells among Biomphalaria glabrata hemocytes: large cells with a tubulo-vesicular compartment, a component of the endocytic system, and with numerous mitochondria and large aggregates of glycogen particles; medium-size cells poor in organelles and glycogen; and small cells with organelles and few secretory granules. Other small hemocytes can be interpreted as juvenile cells. B. glabrata hemocytes contain few enzymes and do not show specific secretory granules, except for a subpopulation of large cells richer in acid phosphatase vesicles. Hemocytes have different aspects corresponding to different physiological states and their transitions: in quiescent hemocytes, the cell cortex is narrow and organelles are scattered in the cytoplasm, both in circulating cells characterized by thin-folded filopods and large macropinocytic vacuoles and in sedentary cells in which extended filopods connect to the extracellular matrix. In stress-activated hemocytes, the cortical region is thickened by polymerization of actin, and organelles are gathered around the nucleus. Fixed phagocytes are components of the connective tissue; the presence of numerous lysosomes and residual bodies and of acid phosphatase and peroxidase activities suggests a high phagocytic activity.     

Light, fluorescence and electron microscopic studies of rabbit subclavian glomera.

The subclavian glomera (aortic bodies) of young New Zealand white rabbits were studied with the light, fluorescence, and electron microscopes. Two cell types were identified: type I, granule-containing (chief) cells, and type II, agranular (sustentacular) cells. The type I cells possessed large nuclei, the normal complement of cytoplasmic organelles and numerous electron-opaque cytoplasmic granules. The type II cells were agranular with attenuated cytoplasmic processes which partially or completely ensheathed the type I cells. The glomera were well vascularized. Capillary endothelial cells contained numerous pinocytotic vesicles, but few fenestrae. Two profiles of nerve terminals were observed. One, apposing the type I cells, contained numerous electron-lucent vesicles, several dense-cored vesicles, mitochondria and possessed membrane specializations resembling those usually observed in synaptic zones. The other profile contained abundant mitochondria and a few electron-lucent and dense-cored vesicles. Structural specializations were not observed on the apposed membranes of these terminals or adjacent to type II cells. Fluorescence histochemistry revealed an intense yellow-green fluorescence in the glomera, which indicated the presence of biogenic amines, possibly primary catecholamines or an indolamine. The electron-opaque granules observed in the type I cells were believed to be the storage sites for these amines. The subclavian glomera were found to be morphologically similar to the carotid body which is a known chemoreceptor.     

Glycogen accumulation in the parathyroid gland of the rat after fluoride ingestion

Summary The parathyroid glands of young male rats given 150 ppm fluoride in their drinking water for 10 weeks were examined by transmission electron microscopy. As a result of fluoride ingestion, the parathyroid chief cells of the experimental animals accumulated glycogen in excess of that seen in control animals given distilled drinking water for the same time period. In the majority of active chief cells, glycogen granules were diffusely spread throughout the cytoplasm as single granules or in small deposits. Large aggregations of glycogen granules were also seen within intercellular spaces. Accompanying the increase in glycogen was a rise in the number and development of the organelles associated with protein synthesis and secretion. The accumulation of glycogen is similar to that in hyperparathyroidism caused by chronic stimulation and prolonged secretory activity of the parathyroid gland. The results of this study suggest that increased amounts of glycogen occur in hyperactive chief cells of the parathyroid in response to the ingestion of large doses of fluoride.     

Morphological and ultrastructural changes in vegetative cells and heterocysts of Anabaena variabilis grown with fructose.

The morphology and ultrastructure of Anabaena variabilis grown in medium with and without 40 mM fructose were compared. Vegetative cells and young heterocysts in fructose-supplemented medium were significantly larger, were filled with glycogen granules, and had fewer thylakoids. Developing heterocysts contained large numbers of glycogen granules well into mature stages, and envelope formation was precocious. As heterocysts enlarged in fructose medium, their shape became more broadly oblong compared with the more rectangular heterocysts in fructose-free medium.     

Salivary gland of the tick vector of east coast fever. IV. Cell type selectivity and host cell responses to Theileria parva

Responses of cells in the tick salivary gland to parasitism by Theileria parva were studied by electron microscopy. The gland is composed of three distinct types of acini (I, II, III) which together include ten or more different cell types. Of some 30 infected cells observed in the present study, all were E-cells of acinus III. The parasite thus exhibits a high degree of selectivity for acinus and cell type. The glandular cell invaded undergoes massive hypertrophy and accumulates glycogen deposits in its cytoplasm which may serve as an energy source for the growing intracellular parasite. As synthesis of its secretory material declines the product is packaged in progressively smaller secretory granules. The extensive arrays of endoplasmic reticulum are dismantled and eliminated in autophagic vacuoles. Excess secretory granules are also broken down by crinophagy. After 4 days, sporogony is completed and the host cell contains 30,000–50,000 sporozoites in an electron-lucent cytoplasm largely devoid of cytomembranes and secretory granules. Mitochondria are still present and normal in appearance. The loss of basophilia and secretory granules observed heretofore by light microscopy have been attributed to ingestion and destruction of host organelles by the parasite. The pallid appearance of the cytoplasm has been interpreted as a sign of impending degeneration of the host cell. In electron micrographs no ingestion of organelles by the parasite or degenerative changes were found. The host cell clearly remains viable and metabolically active throughout sporogony. The striking changes in its ultrastructure result from active elimination of organelles and inclusions by the host cell itself in response to parasitism.     

Fine structure of melanocytes and macrophages in the Harderian gland of the mouse

The presence of dendritic cells containing melanin granules has been demonstrated employing silver impregnation and electron microscopy in the interstitial tissue of the Harderian gland of the mouse. Two types of melanocytes, either with or without the various developmental stages of melanin granules, were found in the gland. Cells with developing granules were more dendritic and contained a large number of cytoplasmic organelles. The other cells were ellipsoidal or slender in shape and contained few cytoplasmic organelles and a large number of fully melanized granules, but no developing granules. In general, the granules of the Harderian gland melanocytes resembled granules from other organs (particularly the skin of the eyelids). The general size range of the granules was 0.2-0.9 micron. Each granule was enclosed by a membrane. The Harderian gland macrophages contained fully pigmented melanin granules of various sizes. The granules were enclosed by a membrane either singly or in groups. Some of the melanin granules within the phagosomes showed signs of degradation, revealing the underlying matrix.     

The expression and distribution of dense granule proteins in the enteric (Coccidian) forms of Toxoplasma gondii in the small intestine of the cat

The expression and distribution of dense granule proteins in the enteric (coccidian) forms of Toxoplasma gondii in the small intestine of the cat. Experimental Parasitology 91, 203-211. The expression and location of the dense granule proteins (GRA1-6 and NTPase) in the merozoite and during asexual and sexual development of Toxoplasma gondii in the small intestine of the cat (definitive host) was examined by immuno-light and electron microscopy. This was compared with that of tachyzoites and bradyzoites present in the intermediate host. It was found that the merozoite contained the characteristic apical organelles plus a few large dense granules. By immunocytochemistry, dense granules in merozoites were negative for GRA proteins 1 to 6 in contrast to both tachyzoites and bradyzoites in which dense granules were positive for all six proteins. The GRA proteins were associated with the parasitophorous vacuole (PV) during tachyzoite and bradyzoite development but were absent from the PV of the enteric stages. However, the merozoite dense granules were positive for NTPase, which was similar to the tachyzoite while this antigen was down regulated in the bradyzoite. The apparent release of the NTPases into the PV formed by merozoites was also similar to that described for the tachyzoite, possibly reflecting the relative metabolic activity of the various stages. This study shows that the majority of GRA proteins have a similar stage-specific expression, which is independent of NTPases expression. These observations are consistent with T. gondii having a different host parasite relationship in the enteric forms, which does not involve the GRA proteins 1-6.     

Liver ultrastructure and a new cell type in the Japanese newt, Cynops pyrrhogaster.

The liver of the Japanese newt, Cynops pyrrhogaster, has been investigated using light, scanning, and transmission electron microscopy. Hepatic parenchyma was composed of clusters and cords or tubules of polyhedral cells separated by a sinusoidal net. Hepatocytes had spherical, euchromatic nuclei with one or more nucleoli and stacked mitochondria with sparse cristae and dense bodies. Rough endoplasmic reticula formed peribiliary stacks and diffusely scattered vesicles and tubules. Smooth endoplasmic reticula were more pronounced in glycogen-rich hepatocytes. Most hepatocytes contained peroxisomes, Golgi complexes and large numbers of fat droplets within the cytoplasm along with glycogen. Some cells were mainly glycogen-storing and contained few or no fat droplets. A special feature of the newt liver was biliary atresia. Bile canaliculi had short, stout microvilli which were entirely atretic in some canaliculi. Canaliculi were sealed off by junctional complexes including zonulae occludentes and maculae adherentes. The latter showed extraordinary wider desmosomal gaps in the vicinity of the atretic bile canaliculi. The sinusoid wall was non-distinctive and contained fenestrated endothelial cells connected to Kupffer cells by zonulae occludentes. A distinctive new cell type (OG cell) was observed in the newt liver. These cells were found individually or in small clusters in proximity with the sinusoidal surfaces. They had small nuclei, a paucity of cytoplasmic organelles, but numerous, unique, osmiophilic granules of two distinct types. Less numerous Type I granules contained homogeneous electron-dense material, and a predominant Type II granule contained circumferentially arranged subparticulation. Granules of both types were detected within the cytoplasm of endothelial cells and within sinusoids together with blood elements. The function of this secretory type cell remains obscure, though it may represent a stage of melanophore.     

Light and electron microscopy on the sporulation of the oocysts of Eimeria brunetti. I. Development of the zygote and formation of the sporoblasts

The initial stages of sporulation in oocysts of Eimeria brunetti were examined in samples sporulated at 27 degrees C for 0, 12 and 24 hours. The initial zygote was found to be roughly spherical and to contain a number of polysaccharide granules which were congregated in one region of the organism. The cytoplasm also contained some strands of rough endoplasmic reticulum together with a number of mitochondria, some Golgi bodies, and some electron translucent vacuoles. The nucleus was large, with amorphous nucleoplasm and a nucleous. The cytoplasmic mass of the zygote was limited by a single unit membrane which possessed some micropores. After initiation of the sporulation, the metabolic activity of the organism appeared to increase as evidenced by the augmentation in the cytoplasm of the amounts of rough endoplasmic reticulum, number of Golgi bodies, and the appearance of polyribosomes. However, at this stage, the presence of large spherical bodies (anlagen of the refractile bodies of the sporozoites) constituted the most obvious change in the cytoplasm of the organism. After nuclear division the daughter nuclei were situated well separated in the cytoplasm and the polysaccharide granules were evenly distributed throughout the cytoplasm of the zygote. Eventually four sporoblasts were formed by invaginations of the limiting membrane. Each sporoblast was limited by a unit membrane and contained a nucleus, and the same cytoplasmic organelles as found in the zygote. The development of the sporoblast was initially accompanied by the appearance of a second limiting membrane.     

Ultrastructure of developing Ascaris larvae undergoing lipid to carbohydrate interconversion.

Triglyceride utilization is correlated with glycogen resynthesis in developing Ascaris suum larvae. Glycogen content, determined by amyloglucosidase hydrolysis at 2-day intervals, decreases sharply during embryonation from 15% (per mg dry weight) at day 4 to 2% at day 12. Thereafter glycogen increases 3-fold through day 20, marking the resynthesis period. Triglyceride lipid droplets are confirmed primarily to the posterior half of the larvae and mark the site of the interconversion. Although they serve as precursors to glycogen, only a small diminution was observed ultrastructurally. Glycogen accumulation, on the other hand, correlates well with increases determined biochemically. alpha-glycogen builds up among lipid droplets, while beta-glycogen concentrates in the cytoplasm of somatic muscle cells paralleling myofibril development. Dense granules, restricted to the lipid body region, are considered as the possible subcellular site for the enzymatic conversion.     

The influence of buffers during fixation on the appearance of smooth endoplasmic reticulum and glycogen in hepatocytes of normal and glycogen-depleted rats.

Liver tissue of normal and glycogen depleted rats was prepared for transmission electron microscopy by perfusion fixation and subsequent osmication in the presence of various buffers, dehydration in aethanol and embedding in epon. The use of Na/K-phosphate or Na-cacodylate to buffer glutaraldehyde led to similar appearance and distribution of SER. When Na-cacodylate was used during osmication, more SER membranes were retained but less accumulations of glycogen were found than after osmication in the presence of Na/K-phosphate. Fixation with s-collidine buffered osmium led to an easily recognisable network of SER comprising wide tubules whereas glycogen was hindered to be stained. Veronal acetate or Na-cacodylate supplemented with sucrose resulted in marked dilation and disintegration of SER. A similar effect was obtained when Na/K-phosphate or Na-cacodylate was used in hyposmolar concentration as buffer for glutaraldehyde. Liver of fasted rats or glucagon-treated rats after perfusion with Na/K-phosphate buffered glutaraldehyde and osmication in the presence of Na/K-phosphate or Na-cacodylate comprised glycogen-depleted hepatocytes which contained abundant SER membranes occupying the entire space between other organelles even in samples harvested 3 h after glucagon administration. The diversity in appearance and distribution of SER and glycogen granules, which depends to a large extend on the buffer used, suggests that SER membranes may not be sufficiently stabilized during aldehyde fixation and osmication. We thus consider it likely that large accumulations of glycogen granules are the consequence of disintegration of SER membranes during processing rather than they represent the morphologic substrate of physiological degradation of SER membranes in the course of glycogen synthesis and deposition.     

Secretion of multilamellar whorls by Eimeria tenella zoites.

Multilamellar whorls were demonstrated by transmission electron microscopy to be associated with sporozoites and all generations of merozoites of Eimeria tenella, in chicken cecal tissue fixed without tannic acid or ruthenium red at room temperature. Whorls were found within the parasitophorous vacuoles of recently invaded cells at all stages of development, suggesting a role in the formation of the host parasite interface. Whorls were also associated with intraluminal third-generation merozoites prior to host cell invasion and appeared to be secreted directly through the pellicle. Membranous sheaths, shown by serial sectioning to be derived from intracellular whorl material, were observed enveloping some intraluminal merozoites. In many third-generation merozoites, whorl material was located within discrete novel organelles (here termed lamellosomes) located in the apical region. These densely staining spherical organelles were morphologically distinct from micronemes and rhoptries and were one-third the size of dense granules. These findings confirm that whorls are nonartifactual secretions whose lamellar organization is lost during normal fixation on ice without tannic acid. It is hypothesized that whorls secreted prior to invasion are involved in protection of the motile zoite, immune evasion, or some aspect of gliding motility.     

Fasciola hepatica: Stereological analysis of vitelline cell development

Cytomorphosis of vitelline cells in Fasciola hepatica has been studied quantitatively by means of a Kontron Videoplan computerized image analyser. The process of vitelline cell development was subdivided into four characteristic phases: the stem cell, the intermediate type 1 cell, the intermediate type 2 cell, and the mature cell. The whole cell and the following constituent organelles, the nucleus, nucleolus, mitochondria, granular endoplasmic reticulum (GER), secretory granules, glycogen, heterophagosomes, and lipid, were analysed at each phase. Results indicated that there was a significant increase in nuclear size between the two intermediate cell stages, and a significant increase in nucleolar size between the stem cell and intermediate type 1 cell; the changes were related to possible gene activation, ribosome production, and cell synthesis required for both cell growth and secretory production. Mitochondria increased in number and showed changes in volume and surface area of whole organelles and their cristae such that these correlated with the energy demands of growth and synthesis. The GER increased its average total volume some 16 times and its average total surface area some 25 times between the stem cell and mature cell stages. Even this increase masked the true extent of membrane production by this system, since membrane was transferred to secretory granules; in reality the GER or GER-derived membranes increased more than 42 times between the stem cell and mature cell stages. Shell globules and glycogen eventually contributed 21 and 20%, respectively, to cytoplasmic volume, while heterophagosomes contributed 14% and lipid only 3%. Residual cytoplasm was shown to be an important component in cytomorphosis, comprising never less than 40% of the total cytoplasmic volume and it was shown to increase prior to or parallel with the development and expansion of other systems.