The mystery of the unstained Golgi complex cisternae

Identification and ultrastructural characterization of the Wolbachia symbiont in Litomosoides chagasfilhoi

BACKGROUND

Filarial nematodes are arthropod-transmitted parasites of vertebrates that affect more than 150 million people around the world and remain a major public health problem throughout tropical and subtropical regions. Despite the importance of these nematodes, the current treatment strategies are not efficient in eliminating the parasite. The main strategy of control is based on chemotherapy with diethylcarbamazine, albendazole and ivermectin. In the 1970s, it was found that some filarids possess endosymbiotic bacteria that are important for the development, survival and infectivity of the nematodes. These bacteria belong to the genus Wolbachia, which is a widespread and abundant intracellular symbiont in worms. Knowledge about the structure of the bacteria and their relationship with their nematode hosts may allow new perspectives for the control of filarial nematodes.

METHODS

In this study, we used transmission electron microscopy combined with three-dimensional approaches to observe the structure of the endosymbiont of the filarial nematode Litomosoides chagasfilhoi, an experimental model for the study of lymphatic filariasis. In addition, the bacterium was classified based on PCR analyses.

RESULTS

The bacterium was mainly found in the hypodermis and in the female reproductive system in close association with host cell structures, such as the nucleus and endoplasmic reticulum. Our ultrastructural data also showed that the symbiont envelope is composed of two membrane units and is enclosed in a cytoplasmic vacuole, the symbiosome. Molecular data revealed that the bacterium of L. chagasfilhoi shares 100% identity with the Wolbachia endosymbiont of Litomosoides galizai.

CONCLUSIONS

Here we described ultrastructural aspects of the relationship of the Wolbachia with the filarial nematode Litomosoides chagasfilhoi and the findings lead us to consider this relationship as a mutualistic symbiosis.

Toxoplasma gondii-skeletal muscle cells interaction increases lipid droplet biogenesis and positively modulates the production of IL-12, IFN-g and PGE2

Background

The interest in the mechanisms involved in Toxoplasma gondii lipid acquisition has steadily increased during the past few decades, but it remains not completely understood. Here, we investigated the biogenesis and the fate of lipid droplets (LD) of skeletal muscle cells (SkMC) during their interaction with T. gondii by confocal and electron microscopy. We also evaluated whether infected SkMC modulates the production of prostaglandin E₂ (PGE₂), cytokines interleukin-12 (IL-12) and interferon-gamma (INF-g), and also the cyclooxygenase-2 (COX-2) gene induction.

Methods

Primary culture of skeletal muscle cells were infected with tachyzoites of T. gondii and analysed by confocal microscopy for observation of LD. Ultrastructural cytochemistry was also used for lipid and sarcoplasmatic reticulum (SR) detection. Dosage of cytokines (IL-12 and INF-g) by ELISA technique and enzyme-linked immunoassay (EIA) for PGE₂ measurement were employed. The COX-2 gene expression analysis was performed by real time reverse transcriptase polymerase chain reaction (qRT-PCR).

Results

We demonstrated that T. gondii infection of SkMC leads to increase in LD number and area in a time course dependent manner. Moreover, the ultrastructural analysis demonstrated that SR and LD are in direct contact with parasitophorous vacuole membrane (PVM), within the vacuolar matrix, around it and interacting directly with the membrane of parasite, indicating that LD are recruited and deliver their content inside the parasitophorous vacuole (PV) in T. gondii-infected SkMC. We also observed a positive modulation of the production of IL-12 and IFN-g, increase of COX-2 mRNA levels in the first hour of T. gondii-SkMC interaction and an increase of prostaglandin E₂ (PGE₂) synthesis from 6 h up to 48 h of infection.

Conclusions

Taken together, the close association between SR and LD with PV could represent a source of lipids as well as other nutrients for the parasite survival, and together with the increased levels of IL-12, INF-g and inflammatory indicators PGE₂ and COX-2 might contribute to the establishment and maintenance of chronic phase of the T. gondii infection in muscle cell.

Cytochemical characterization of the endomembranous system during the oocyte primary growth in Serrasalmus spilopleura (Teleostei, Characiformes, Characidae)

The morphophysiological changes that occur during oocyte primary growth in Serrasalmus spilopleura were studied using ultrastructural cytochemical techniques. In the previtellogenic oocytes endoplasmic reticulum components, Golgi complex cisternae and vesicles, lysosomes, multivesicular bodies and some electron-dense vesicles react to acid phosphatase (AcPase) detection. The endoplasmic reticulum components, Golgi complex cisternae and vesicles also react to osmium tetroxide and potassium iodide impregnation (KI). These structures, except for the Golgi complex cisternae, are strongly contrasted by osmium tetroxide and zinc iodide impregnation (ZIO). Some electron-dense vesicles are ZIO-stained, while microvesicles in the multivesicular bodies and other large isolated cytoplasmic vesicles are contrasted by KI. At primary oocyte growth, the activity of the endomembranous system and the proliferation of membranous organelles are intense. The biosynthetic pathway of the lysosomal proteins such as acid phosphatase, involves the endoplasmic reticulum, Golgi complex, vesicles with inactive hydrolytic enzymes and, finally, the lysosomes. The oocyte endomembranous system have reduction capacity and are involved in the metabolism of rich in SH groups.

Ultrastructural cytochemistry of the sex pheromone glands of Lutzomyia cruzi male sand flies (Diptera: Psychodidae: Phlebotominae)

The sex pheromone glands of Lutzomyia cruzi male sand flies (Diptera: Psychodidae) were analyzed by cytochemical techniques. In adult males, the epithelium at the fourth abdominal tergite is modified into a glandular epithelium, with large columnar gland cells located side by side. The gland cell cytoplasm contains a large number of mitochondria and peroxisomes, the latter with positive (electron-dense) reaction for catalase, a typical peroxisomal enzyme marker. The gland cell cytoplasm also contains a central vacuolated area, with a large number of electron-lucent vacuoles, not limited by a unit membrane. In well-preserved preparations such vacuoles present a homogenous and slightly electron-dense content, typical of lipid droplets. Indeed, incubation of the tergites with imidazole-buffered osmium tetroxide (to detect lipids) resulted in positive reaction in these vacuoles, as well as in between the microvilli of the gland cells. Use of the osmium-potassium iodide (Os-KI) technique allowed to demonstrate the presence of several endoplasmic reticulum (ER) profiles, as expected in secretory cells. Our data suggest that ER, lipid droplets and peroxisomes are involved in the sand fly pheromone biosynthesis.

Fine structure of the salivary glands of Triatoma infestans (Hemiptera: Reduviidae)

The fine structure of the salivary glands of adult Triatoma infestans (Hemiptera: Reduviidae) bugs has been analyzed. Stereomicroscopy and scanning electron microscopy showed that each insect presents a pair of salivary glands, each pair containing three distinct units (main, supplementary, and accessory) with different sizes and colors. Transmission electron microscopy demonstrated that all gland units consist of a monolayer of epithelial cells surrounding a large central lumen. The gland units are enveloped by a thick basal lamina containing bundles of muscle cells. Microvilli are present at the apical plasma membrane domain of the gland cells, thus enlarging the available membrane area for saliva secretion towards the large gland lumen, although occasionally budding vesicles could be observed among the microvilli. Cytochemical analysis showed that the salivary gland cells of T. infestans present abundant endoplasmic reticulum profiles and several lipid droplets.

Surface membranes, Golgi complexes, and vacuolar systems

In the absence of fossils, the cells of vertebrates are often described in lieu of a general animal eukaryote model, neglecting work on insects. However, a common ancestor is nearly a billion years in the past, making some vertebrate generalizations inappropriate for insects. For example, insect cells are adept at the cell remodeling needed for molting and metamorphosis, they have plasma membrane reticular systems and vacuolar ferritin, and their Golgi complexes continue to work during mitosis. This review stresses the ways that insect cells differ from those of vertebrates, summarizing the structure of surface membranes and vacuolar systems, especially of the epidermis and fat body, as a prerequisite for the molecular studies needed to understand cell function. The objective is to provide a structural base from which molecular biology can emerge from biochemical description into a useful analysis of function.

Selective translocation of different markers in the ante- and retrograde pathways between the Golgi apparatus and the rough endoplasmic reticulum in a hybridoma cell line

We examined the effects of brefeldin A (BFA, 10 micrograms/ml), an inhibitor of protein transport, on the redistribution of different markers of the Golgi apparatus (GA) in hybridoma H35 cells to examine selective transport of marker molecules between the rough endoplasmic reticulum (RER) and the GA. In H35 cells, the GAs had several cisternae with cis and trans faces as deduced by morphology such as relationship with RER and secretory granules. Thiamin pyrophosphatase (TPPase) was distributed in the trans elements, mannosidase II (man II) was in the cis-medial elements, and deposits of Zinc-Iodide-Osmium (ZIO) staining were localized in the cis/intermediate compartment. Upon BFA treatment for 5 min, man II and TPPase were redistributed in all cisternae. After 10 min of BFA treatment, TPPase activity was observed only in the RER, while the cis/intermediate compartment as evidenced by ZIO staining and man II remained. Upon clearance of BFA from the medium, cisternal structures with man II and ZIO staining reappeared at 30 min. TPPase activity was detected in the GA only after 120 min. Thus, in the retrograde pathway, the trans marker, TPPase moves earlier than the cismedial markers, man II and ZIO staining, whereas in the antegrade pathway, the cis-medial markers move earlier than the trans marker. These results suggest that BFA first alters the characteristic enzyme localization before the GA vanishes into the RER, and that selective transport mechanisms may exist for components of different stacks of the GA.

The relationship between synthesis of secretory products and reducing capacity in pancreas and parotid acinar cells

The secretory products in exocrine pancreas acinar cells in utero were found to reduce osmium tetroxide. This reducing capacity was also exhibited by adult pancreas and parotid glands in different phases of synchronized secretion, and after single or chronic administration of a secretagogue, pilocarpine or isoprenaline. In utero, the reducing capacity appeared in the pancreas concomitantly with the synthesis of secretory products, and was limited to the transitional vesicles on the cis Golgi side. After birth, osmium staining occurred in the cis Golgi vesicles and cisternae of both glands. In the chronically-treated parotid gland, where the occupational programme for secretory proteins had been altered, the reducing capacity was diminished, resembling that in embryonic exocrine pancreas.

Influence of calcium and amino acids on the osmium impregnation of the endoplasmic reticulum

The aim of this study was to define further the interaction between osmium and organelle content in cells prefixed with glutaraldehyde. We have studied the reaction of osmium with divalent or trivalent cations (calcium, barium, zinc, aluminum, and iron) and various amino acids in the same conditions prevalent in histological techniques, in particular with Thiéry's technique of metal impregnation. Experiments were carried out in vitro in test tubes, on cellulose acetate discs, or with an immunodiffusion apparatus. Some experiments were also carried out with tissue extracts (kidney and intestine). Our studies suggest that calcium is in general essential for the formation of osmium black, but also that lysine is reactive even in the absence of calcium and that a few amino acids--such as tryptophan, ornithine, cysteine, and aspartic acid--are only slightly reactive in the absence of calcium. Other amino acids do not seem to participate in the endoplasmic reticulum osmium impregnation even in the presence of calcium ions. Our studies also suggest that osmium reactivity reflects calcium binding sites and not only calcium content.

Secretory pathways in animal cells: with emphasis on pancreatic acinar cells

Studies over the past three decades have clearly established the existence of at least two distinct pathways for the intracellular transport and release of secretory proteins by animal cells. These have been identified as the regulated and constitutive pathways. Many observations have indicated that in certain cells, such as those of the exocrine pancreas and parotid glands at least, these pathways coexist in the same cells. Although the general scheme of protein transport within these pathways is well established, many fundamental aspects of intracellular transport remain to be unraveled. How are proteins transported through the endoplasmic reticulum? How are the transitional vesicles formed and what are the underlying mechanisms involved in their fusion with the cis-Golgi cisterna? Even the general mode of transfer through the Golgi stack is debated: Is there a diffusion through the stack by flow through intercisternal tubules and openings or is there a vesicle transfer system where membrane quanta hop from one cisterna to the other? What is the fate of secretory proteins in the trans-Golgi area and by what mechanisms is a fraction of newly synthesized molecules of a given secretory protein released spontaneously while the majority of such nascent molecules are diverted into a secretory granule compartment? In this review, we have examined these and other aspects of intracellular transport of secretory proteins using pancreatic acinar cells as our reference model and we present some evidence to support the existence of a paragranular pathway of secretion associated with secretory granule maturation.

Golgi complex beads and the transition region

Secretory proteins and membranes move in transfer vesicles from the rough endoplasmic reticulum through the transition region to the outer saccule of the Golgi complex. In both arthropod and vertebrate cells, the GC beads are a characteristic structural component of the transitional region. The beads are particles about half the size of ribosomes arranged equidistantly from one another and the smooth face of the ER. In an active GC, the beads are in rings through which the ER membrane emerges to form transfer vesicles. The beads may be part of the energy-dependent step required for the movement of proteins along eht secretory pathway, since they lose their ring arrangement under conditions that lower cellular ATP. The beads are organizers for Golgi complexes in the sense that they are the first recognizable components of new GCs as they arise from ER. Arthropod GC beads, but not those of vertebrates, can be visualized through their reaction with bismuth in vivo and in fixed tissue. Useful paradigms for traffic between the ER and the GC need to combine structural and biochemical information. Insect fat body, with its readily resolvable bismuth-strained beads and easily fractionated cell components may have particular value for this problem.

Prolonged osmification of stomach epithelium

Osmium impregnation was used upon the mice stomach epithelium to show possible differences in staining during differentiation. In the cells of the stratified gastric epithelium of 14-day-old mice embryos Os black was completely lacking in the Golgi complex. In some but not all cells the staining appears in the perinuclear space and in the endoplasmic reticulum. In the mucoid cells 1 and 8 days after the birth the osmiophility is not uniformly distributed throughout the endomembrane segments, except the cis face of the Golgi complex which is heavily stained. Our results indicate on the variability of the reduction capacity of particular endomembrane segments during differentiation and among the cells at the definite developmental stage.

Reduction capacity of untreated and of repeatedly isoproterenol treated parotid gland of the mouse

Osmium impregnation was used to show possible differences of reduction capacity of perinuclear space, rough endoplasmic reticulum and the Golgi apparatus of unstimulated mouse parotid gland and in the gland after repeated pharmacological doses of isoproterenol. There were some significant differences between the staining of acinar and duct cells. In all intercalated and striated duct cells the staining is dense in the perinuclear space and in the rough endoplasmic reticulum. Osmiophility was not detected in the Golgi complex of intercalated duct cells. The staining was also lacking in the perinuclear space and endoplasmic reticulum of the acinar cells. The cis face of the Golgi complex and numerous transitional vesicles in the acinar cells showed variability of the reduction capacity of their membrane segments. In chronically treated acinar cells Os black was lacking in the Golgi cisternae, except that the numerous transitional vesicles were heavily stained. These results reveal characteristic differences of reduction capacity of endomembrane compartments in different parotid glandular cells, as well as between untreated and treated acinar cells.

Fragmentation and partitioning of the Golgi apparatus during mitosis in HeLa cells

Osmium impregnation was used to determine the number of Golgi apparatus in both interphase and mitotic HeLa cells. The number was found to increase substantially during mitosis to the point where random partitioning alone would explain the nearly equal numbers found in each daughter cell.

Lead-dependent deposits in diverse synaptic vesicles: suggestive evidence for the presence of anionic binding sites

We have observed electron dense deposits dependent on incubation of aldehyde-fixed tissues with lead ions within synaptic vesicles of several types of neurons that differ in the neurotransmitters utilized and in the secretory granules of the adrenal medulla. Evidently, vesicle components that can interact with lead ions are widespread. A plausible explanation for the occurrence of the deposits is the presence of anionic binding sites within the vesicles. This would agree well with other biochemical, cytochemical, and immunocytochemical evidence, such as that indicating the presence of sulfated macromolecules in certain synaptic vesicles. Anionic binding sites could play significant roles by participating in processes such as Ca2+ storage, stabilization of pH gradients, or the control of osmotic phenomena.

Intramural nerves and interstitial cells revealed by the Champy-Maillet stain in the opossum esophagus

The 3 layers of smooth muscle of the opossum esophagus exhibit distinctly different and characteristic functions in response to nerve stimulation. These behaviors might be related to differences in patterns of innervation. Serial sections, stained with osmic acid and zinc iodide, were examined from all parts of the esophagus to describe in full the innervation of opossum esophageal smooth muscle. Linear beaded structures identified as terminal nerves were abundant in all 3 layers of smooth muscle. They were aligned with muscle bundles in bundles of 1-5 in mucosal muscle and up to about 10 in the longitudinal layer of muscularis propria. In the circular layer of muscularis propria they were less dense and more arborized and they crossed the muscle obliquely to also innervate bipolar interstitial cells; these cells resembled type III interstitial cells of Cajal, were specific for the circular muscle layer and were uniformly distributed throughout the thickness of that layer. Their distribution density in the circular muscle was slightly greater, 8777/cm2 in the most caudad 1.5 cm of the esophagus (which encompasses the sphincter) than in the 6 cm above that level. Terminal nerves also innervated submucosal glands, vessels and the epithelium. Ganglion cells and nerve bundles in the submucous and myenteric plexuses were variably stained. Ganglia of the latter plexus contained intraganglionic laminar endings as described previously in other species. In the striated muscle there were nerves terminating in motor end-plates. Other leafy stellate cells resembling interstitial cells of Cajal of other types were stained, as were oval interstitial cells.

The relationship between the morphology of cell organelles and kinetics of the secretory process in male sex accessory glands of mice

Two male sex accessory glands of the mouse, seminal vesicle and coagulating gland, were compared with the aim of relating differences in the morphology of organelles to the kinetics of the secretory process. The epithelial cells of the two glands were assessed by morphometric analysis, cytochemical staining, and electron-microscopic autoradiography after administration of a labeled amino acid. The rough endoplasmic reticulum of the seminal vesicle comprised narrow parallel cisternae, while that of the coagulating gland was greatly distended and occupied a much larger percentage of the cytoplasmic volume. Radioactively labeled products were secreted much more rapidly in the seminal vesicle than in the coagulating gland. The primary point of difference in kinetics of intracellular transport between the two glands was in exit of material from the rough endoplasmic reticulum. The more rapid drainage of the rough endoplasmic reticulum may be related to its relatively greater membrane surface density and lesser internal volume. In contrast, similarities in size and cytochemical staining in the Golgi apparatus of the two glands were accompanied by similar kinetics of intracellular transport of secretory protein through this organelle.

Early and late sarcoplasmic reticulum changes in doxorubicin cardiomyopathy. An ultrastructural investigation with the zinc iodide-osmium tetroxide (ZIO) technique

The sequence of myocardial changes in the mouse induced by doxorubicin (Dx) treatment (10 mg/kg i.v.) has been investigated by electron microscopy with the help of the zinc iodide-osmium tetroxide (ZIO) technique. Accumulation of ZIO-reactive material, possibly oxidized glutathione and other disulfides, in the sarcoplasmic reticulum (S.R.) is among the earliest (1 h after Dx injection), more prominent and persistent findings (up to 100 days). It may have a pathogenic relationship with a number of functional and morphologic changes occurring in myocardial cells, including impairment of calcium transport and contractility, S.R. dilation up to extensive vacuolization, as well as inhibition of DNA, RNA and protein synthesis leading to atrophy and disruption of sarcomeres. The latter finding, first appearing in a few cells 4 to 7 days after Dx and progressively increasing in severity and extension during the next 3 months, may represent a key factor in the evolution of chronic cardiomyopathy to cardiac insufficiency. In most cells, only a minority of mitochondria showed obvious ultrastructural lesions, which were first observed 24 h after treatment and disappeared by the end of the first month, when no more mitochondrial damage was found outside degenerating cells. The myocardium of mice receiving multiple Dx injections (4 mg/Kg, 10 times, or 9 mg/Kg, 5 times) showed the same changes observed in animals treated with a single dose, though they were more severe and extensive.

A clathrin-coated, Golgi-related compartment of the insulin secreting cell accumulates proinsulin in the presence of monensin

When the intracellular transit of 3H-labeled (pro)-insulin polypeptides is perturbed by monensin in the pancreatic B-cell, proinsulin conversion is impaired and the radioactive peptides accumulate in a clathrin-coated membrane compartment related to the Golgi apparatus. Clathrin was demonstrated by immunocytochemistry using the postembedding protein A-gold technique. The coated compartment, which is dilated by monensin, comprises Golgi cisternae with condensing secretory material and newly formed secretory granules; under monensin block, the noncoated (storage) secretory granules do not become significantly labeled. These data suggest that an unperturbed passage through a Golgi-related, clathrin-coated membrane compartment which subsequently matures into noncoated secretory granules is needed for the normal processing of (pro)insulin polypeptides.

The induction and distribution of an insect ferritin--a new function for the endoplasmic reticulum

Three insect tissues have particular roles as filters to maintain the fluid composition of the hemolymph. Water and ions enter and leave through the midgut. The pericardial cells filter circulating hemolymph. Malpighian tubules, often with the rectum, allow resorption from a hemolymph filtrate that passes to the hindgut. All three tissues have plasma membrane infolds making a reticulum on their hemolymph surfaces, and all three have RER leading to SER extensions into their reticula. SER is a catch-all description for membranes lacking ribosomes in the pre-Golgi complex set of compartments of the vacuolar system. Some kinds of SER are well known for their role in housing enzymes for steroid metabolism and for detoxification. The SER ramifying within the plasma membrane reticular systems of tissues concerned with hemolymph filtration contains ferritin, suggesting that this SER has another, different function. In contrast to vertebrate cells, where ferritin is confined to the cytosol and lysosomes, we have found that in Calpodes and perhaps in most insects, ferritin occurs in the vacuolar system and not in the cytosol. Ferritin occurs naturally in the RER and SER of cells at the hind end of the midgut, in pericardial cells and in the yellow region of the Malpighian tubules. Additional ferritin is induced by loading the gut or hemolymph with iron. Overloading with iron causes ferritin secretion to the gut lumen. We propose that the SER in these cells functions in iron homeostasis by holding ferritin for loading and unloading as it moves to and from the reticulum at the cell surface where it can be maximally exposed to extracellular fluid flow.