Nuage material and the origin of dense-core vesicles in oocytes of Nassarius reticulatus (Mollusca,Gastropoda)

Summary

In late previtellogenic oocytes nuage material accumulates in the vicinity of the nucleus and is often seen to be intimately associated with cisternae of endoplasmic reticulum (ER). A similar association observed in Ilyanassa has given rise to the proposition that nuage granules become completely enclosed in an envelope of ER and that this structure is transformed into so-called double-membrane vesicles, organelles which have only been found in eggs of Ilyanassa and Nassarius. This study provides evidence that, in Nassarius, the association of nuage material with ER has a temporary character. At later stages the nuage granules dissociate from the ER, move away from the nucleus, and become surrounded by mitochondria. Eventually they disintegrate. Evidence is presented that double-membrane vesicles originate from cisternae of ER by the accumulation and transformation of material within the lumen of the cisternae. Since only a single membrane is present in these vesicles, and a dense core is consistently found if the appropriate fixation is employed, I suggest that these vesicles be called dense-core vesicles instead of double-membrane vesicles.     

Prochlorococcus extracellular vesicles: molecular composition and adsorption to diverse microbes

Extracellular vesicles are small (~50–200 nm diameter) membrane-bound structures released by cells from all domains of life. While vesicles are abundant in the oceans, their functions, both for cells themselves and the emergent ecosystem, remain a mystery. To better characterize these particles – a prerequisite for determining function – we analysed the lipid, protein, and metabolite content of vesicles produced by the marine cyanobacterium Prochlorococcus. We show that Prochlorococcus exports a diverse array of cellular compounds into the surrounding seawater enclosed within discrete vesicles. Vesicles produced by two different strains contain some materials in common, but also display numerous strain-specific differences, reflecting functional complexity within vesicle populations. The vesicles contain active enzymes, indicating that they can mediate extracellular biogeochemical reactions in the ocean. We further demonstrate that vesicles from Prochlorococcus and other bacteria associate with diverse microbes including the most abundant marine bacterium, Pelagibacter. Together, our data point toward hypotheses concerning the functional roles of vesicles in marine ecosystems including, but not limited to, possibly mediating energy and nutrient transfers, catalysing extracellular biochemical reactions, and mitigating toxicity of reactive oxygen species.     

The recognition, distribution and ultrastructure of hydrozoan nerve elements

Silver stained Cordylophora were examined by light and electron microscopy, which provided a general picture of nerve cell forms and distribution for comparison with electron micrographs of osmium-fixed tissues from the same hydroid. Muscle, nerve and neurosensory components were studied in the nectophore of Nanomia (O. Siphonophora) and in the hydromedusae Sarsia and Euphysa by means of vital staining and optical and electron microscopy of epon sections; particular attention was given to relationships and interconnections between the cellular elements of the two marginal nerve rings. Mitochondrial size, numbers and types of vesicles and the occurrence of neurotubules and of parts of sensory cilia may provide useful ultrastructural clues for recognizing nerve elements, but serial sections are often needed to make identification conclusive. In Cordylophora and Nanomia, some neurites contain massed A vesicles (membrane-bounded dense granules) suggestive of neurosecretion (cf. reports on Hydra). However, a small type of A vesicle also occurs at synapses in Sarsia, indicating a probable role here in junctional transmission. Vesicles occur on both sides of some synapses (as previously reported for Cyanea) but on one side only in others, these being the first examples of polarized junctional ultrastructure in coelenterates.     

Nonclathrin Vesicle Coats and Filament Networks in the Transition Zone and trans-Golgi Region of the Golgi Complex of Paramecium

Understanding vesicle trafficking to and through the Golgi stack has been greatly elucidated recently, but the question of what holds the endoplasmic reticulum (ER) and Golgi stack together in many cell types and an explanation of anterograde trafficking in the ER-Golgi transitional zone have not yet been adequately explained. We have studied these problems using both the thin sectioning and the quick-freeze deep-etch (QF-DE) technique on Paramecium cells harvested at different culture ages. Although the Golgi apparatus of Paramecium is made up of many sets of more reduced stacks of cisternae than those of many mammalian cells, the stacks in Paramecium always bear a close relationship to a transitional element of the ER from which non-clathrin-coated transition vesicles arise. In QF-DE replicas two networks of filaments are clearly shown; one is in this ER-Golgi transition zone and the other is on the trans side of the Golgi stack. The network associated with the trans-Golgi region links a number of vesicular elements. The network in the transition zone spans the distance between the ER and the cis-cisterna of the Golgi stack and has branches extending to the coats of the enmeshed nonclathrin-coated transition vesicles. These coats consist of a layer of 11-nm globular elements (the same size as coatomer complexes) which surround the 40-nm-diameter transition vesicles. We conclude that the filamentous network holds the ER and Golgi stack together and prevents the dispersal of the transition vesicles away from this zone. This network may also delineate and stabilize the transitional element within the ER and, finally, help organize anterograde transition vesicle trafficking in this ER-Golgi transition zone.     

ULTRASTRUCTURE OF DEVELOPING SIEVE ELEMENTS IN THLASPI ARVENSE L. I. THE IMMATURE STATE

Immature sieve elements of pennycress (Thlaspi arvense, Brassicaceae) were studied with the electron microscope in connection with studies on virus-infected plants. Immature sieve elements contained cytoplasm rich in organelles and other components: endoplasmic reticulum, dictyosomes and associated smooth and coated vesicles, mitochondria, plastids, ribosomes, microtubules, microfilaments, vacuoles, and nuclei that were sometimes lobed. Tubular P-protein (phloem protein) and one to three granular P-protein bodies also were present in the cytoplasm. Coated vesicles may be involved in formation of the granular P-protein body and in some aspect of cell wall development, for in the latter case, they were often seen united with the plasmalemma. The association of coated vesicles with the P-protein body is discussed with reference to proposed concepts of the origin and function of these vesicles.     

Ultrastructure and a possible function of the intercisternal elements in dictyosomes

The slime-producing dictyosomes in the placentary papillae of Aptenia cordifolia (L.f.) Schwant. show some structural peculiarities: (1) the number of their cisternae is conspicuously large in comparison with those of other cormophyta; (2) the spaces between the extremely flat vesicle-producing cisternae of the maturing face are considerably higher than those between the other cisternae; (3) the intercisternal elements show a pearl-string form rather than a fibrillar form-especially on tangential sections. Based on personal and on cited findings, the following hypothesis is developed: The intercisternal elements effect the compression of the central region of the secretory cisternae. This causes the production of vesicles to remain restricted to the marginal region of the cisternae, even if these cisternae contain hypertonic or soaking substances.     

New Strategies of LIBS-Based Validation of Glycemic Elements for Diabetes Management

Antidiabetic efficacy of medicinal plant cannot be ignored in order to develop drugs without toxicity and side effects. Trace elements present in plant material is responsible for their medicinal nature and hence it is necessary to know the major and minor constituents of the plant material. Laser-induced breakdown spectroscopy (LIBS) is a very efficient and powerful analytical tool to monitor the elements present in sample. The present study deals with the LIBS-based validation of glycemic elements present in Withania coagulans and Cajanus cajan medicinal herbs. The decreasing blood glucose level and improving glucose tolerance test significantly showed that the higher content of Mg and Ca in W. coagulans in comparison to C. cajan is responsible for its significant role in diabetes management, whereas the concentration of other elements are nearly the same in both extracts.     

Transport of rosettes from the golgi apparatus to the plasma membrane in isolated mesophyll cells ofZinnia elegans during differentiation to tracheary elements in suspension culture

Summary Rosettes of six particles have been visualized by freeze-fracture in the protoplasmic fracture (PF) faces of: a) the plasma membrane, b) Golgi cisternae, and c) Golgi-derived vesicles in mesophyll cells ofZinnia elegans that had been induced to differentiate synchronously into tracheary elements in suspension culture. These rosettes have been observed previously in the PF face of the plasma membranes of a variety of cellulose-synthesizing cells and are thought to be important in cellulose synthesis. InZinnia tracheary elements, the rosettes are localized in the membrane over regions of secondary wall thickening and are absent between thickenings. The observation of rosettes in the Golgi cisternae and vesicles suggests that the Golgi apparatus is responsible for the selective transport and exocytosis of rosettes in higher plants, as has been previously indicated in the algaMicrasterias (Giddings et al. 1980). The data presented indicate that the Golgi apparatus has a critical role in the control of cell wall deposition because it is involved not only in the synthesis and export of matrix components but also in the export of an important component of the cellulose synthesizing apparatus. The rosettes are present in the plasma membrane and Golgi vesicles throughout the enlargement of the secondary thickening, suggesting that new rosettes must be continually inserted into the membrane to achieve complete cell wall thickening.Abbreviations EF Golgi vesicles, exoplasmic fracture; the plasma membrane, extracellular fracture - PF protoplasmic fracture     

Intracellular traffic of the lysine and glutamic acid rich protein KERP1 reveals features of endomembrane organization in Entamoeba histolytica

The development of amoebiasis is influenced by the expression of the lysine and glutamic acid rich protein 1 (KERP1), a virulence factor involved in Entamoeba histolytica adherence to human cells. Up to date, it is unknown how the protein transits the parasite cytoplasm towards the plasma membrane, specially because this organism lacks a well‐defined endoplasmic reticulum (ER) and Golgi apparatus. In this work we demonstrate that KERP1 is present at the cell surface and in intracellular vesicles which traffic in a pathway that is independent of the ER–Golgi anterograde transport. The intracellular displacement of vesicles enriched in KERP1 relies on the actin‐rich cytoskeleton activities. KERP1 is also present in externalized vesicles deposited on the surface of human cells. We further report the interactome of KERP1 with its association to endomembrane components and lipids. The model for KERP1 traffic here proposed hints for the first time elements of the endocytic and exocytic paths of E. histolytica.     

Glucose transport in thymocyte plasma-membrane vesicles

Calf-thymocyte membrane vesicles, prepared by hypotonic lysis and homogenization, were isolated by standard centrifugal techniques designed for enrichment of plasma membrane. At 20°C, these vesicles equilibrated with d-glucose and 3-O-methyl-d-glucose more rapidly than with l-glucose. About 25% of the equilibrium d-sugar space (6 μl/mg protein) was very slowly penetrated by l-glucose ( ). The time course of d-sugar accumulation in excess of l-glucose accumulation indicated that this space equilibrated with d-glucose and 3-O-methyl-d-glucose with half-times of approximately 0.2–0.4 min. The remainder of the equilibrium d-sugar space (about 75%) appeared equally accessible to both glucose isomers ( to 5 min). This was confirmed in studies of efflux from preloaded vesicles, where the d-glucose space fell with a short half-time (0.2 min) to the l-glucose space, after which the two isomers exited with the same half-time. Addition of sucrose to increase osmolarity reduced both spaces (specific and non-specific) in a manner which indicated that little if any of the vesicle sugar was bound. This was confirmed by the fact that equilibrium glucose space was independent of glucose concentration and by the fact that vesicles immediately lost their sugar when diluted with water at 0°C. These data indicate the presence of two vesicle types, discriminant and indiscriminant as regards transport of the glucose isomers. Entry of d-glucose into the discriminant (stereospecific) vesicles was temperature sensitive (Q₁₀ > 2), saturable (K_m 2 mM), and was inhibited by phloretin (K_i < 200 μM), N-ethylmaleimide (K_i < 10 mM) and cytochalasin B (K_i < 2 μM), suggesting that these vesicles contain the plasma-membrane glucose carrier. Entry of l- and d-glucose into the indiscriminant vesicles showed none of these properties. The equilibrium-exchange K_m and V were about five times the entry K_m and V, indicating the substrate loading greatly facilitates carrier translocation, at least in the outward direction.     

Calcium‐ and polyphosphate‐containing acidocalcisomes in chicken egg yolk

Background information. Poly P (inorganic polyphosphate) is a polymer formed by P_i residues linked by high‐energy phosphoanhydride bonds. The presence of poly P in bacteria, fungi, algae and protists has been widely recognized, but the distribution of poly P in more complex eukaryotes has been poorly studied. Poly P accumulates, together with calcium, in acidic vesicles or acidocalcisomes in a number of organisms and possesses a diverse array of functions, including roles in stress response, blood clotting, inflammation, calcification, cell proliferation and apoptosis. Results. We report here that a considerable amount of phosphorus in the yolk of chicken eggs is in the form of poly P. DAPI (4′,6‐diamidino‐2‐phenylindole) staining showed that poly P is localized mainly in electron‐dense vesicles located inside larger vacuoles (compound organelles) that are randomly distributed in the yolk. These internal vesicles were shown to contain calcium, potassium, sodium, magnesium, phosphorus, chlorine, iron and zinc, as detected by X‐ray microanalysis and elemental mapping. These vesicles stain with the acidophilic dye Acridine Orange. The presence of poly P in organellar fractions of the egg yolk was evident in agarose gels stained with Toluidine Blue and DAPI. Of the total phosphate (P_i) of yolk organelles, 16% is present in the form of poly P. Total poly P content was not altered during the first 4 days of embryogenesis, but poly P chain length decreased after 1 day of development. Conclusions. The results of the present study identify a novel organelle in chicken egg yolk comprising acidic vesicles with a morphology, physiology and composition similar to those of acidocalcisomes, within larger acidic vacuoles. The elemental composition of these acidocalcisomes is proportionally similar to the elemental composition of the yolk, suggesting that most of these elements are located in these organelles, which might be an important storage compartment in eggs.     

Characterization of the size distribution of unilamellar vesicles by gel filtration, quasi-elastic light scattering and electron microscopy

The size and size distribution of unilamellar phospholipid vesicles present in unsonicated phosphatidic acid and mixed phosphatidic acid/phosphatidylcholine dispersions were determined by gel filtration, quasi-elastic light scattering and freeze-fracture electron microscopy. The vesiculation in these dispersions was induced by a transient increase in pH as described previously (Hauser, H. and Gains, N. (1982) Proc. Natl. Acad. Sci. USA 79, 1683–1687). The resulting phospholipid dispersions are heterogeneous consisting of small unilamellar vesicles (average radius r < 50 nm) and large unilamellar vesicles (average r ranging from about 50 to 500 nm). The smallest vesicles with r = 11 ± 2 nm are observed with dispersions of pure phosphatidic acid, the population of these vesicles amounting to about 80% of the total lipid. With increasing phosphatidylcholine content the radius of the small unilamellar vesicles increases and at the same time the population of small unilamellar vesicles decreases. The average radius of small unilamellar vesicles present in phosphatidic acid/phosphatidylcholine dispersions (mole ratio, 1:1) is 17.5 ± 2 nm, the population of these vesicles amounting to about 70% of the total lipid. By a combination of gel filtration, quasi-elastic light scattering and freeze-fracture electron microscopy it was possible to characterize the large unilamellar vesicles. This population is heterogeneous with its mean radius also increasing with increasing phosphatidylcholine content. After separating the large unilamellar vesicles from small unilamellar vesicles on Sepharose 4B it can be shown by quasi-elastic light scattering that in pure phosphatidic acid dispersions 80–90% of the large unilamellar vesicle population consist of vesicles with a mean radius of 170 nm. In mixed phosphatidic acid/phosphatidylcholine dispersions this radius increases to about 265 nm as the phosphatidylcholine content is raised to 90 mol%.     

Ultrastructure of Elasmobranch and Teleost Erythrocytes

The ultrastructure of circulating erythrocytes of Raja clavata and Torpedo marmorata (Elasmobranchs) and Rutilus rutilus and Gobio gobio (Teleosts) was comparatively described in relation to their function. The existence of intranuclear hemoglobin and the degradation of cytoplasmic organelles are related to hemoglobin storage. Lysosome-like vesicles and microtubular marginal bands are also common elements of these cells. Thus, the presence of numerous cytoplasmic organelles in circulating erythrocytes suggests a certain immaturity, in relation to those in mammals.     

Transposable elements as activators of cryptic genes in E. coli

The concept of transposable elements (TEs) as purely selfish elements is being challenged as we have begun to appreciate the extent to which TEs contribute to allelic diversity, genome building, etc. Despite these long-term evolutionary contributions, there are few examples of TEs that make a direct, positive contribution to adaptive fitness. In E.coli cryptic (silent) catabolic operons can be activated by small TEs called insertion sequences (IS elements). Not only do IS elements make a direct contribution to fitness by activating cryptic operons, they do so in a regulated manner, transposing at a higher rate in starving cells than in growing cells. In at least one case, IS elements activate an operon during starvation only if the substrate for that operon is present in the environment. It appears that E. coli has managed to take advantage of ISelements for its own benefit. This revised version was published online in July 2006 with corrections to the Cover Date.     

Speciation of trace element compounds in samples of biota from marine ecosystems

Abstract

The toxicity, mobility, bioavailability and bioaccumulation of metals are dependent on the particular physico-chemical form in which the element occurs in the environment. Special attention has been paid to metals which are essential for the proper functioning of organisms if present in appropriate amounts but are toxic if in excess (i.e. Se, Cr), and also to non-essential elements (i.e. Hg, Pb, Cd, Sn and As). To assess the potential hazard to the health of marine organisms, qualitative and quantitative analyses of metal species accumulating along the food chain needs to be carried out. This paper reviews the available information on the speciation of trace elements in the food chain in marine ecosystems and the analytical tools used for acquiring reliable information in this field. Advantages and limitations of commonly used techniques indicate that all metal species in different samples need diverse extraction, separation and detection conditions. Although not recommending which procedure is the most suitable to determine a given compound, speciation analysis has the potential to be a powerful tool for the identification of trace element species in biological samples.     

The structure of the Golgi apparatus: a sperm’s eye view in principal epithelial cells of the rat epididymis

 The Golgi apparatus of epididymal principal cells shares many structural features with other cell types. Saccular regions are arranged in a cis-Golgi network, eight flattened saccules, and several trans-Golgi networks (TGNs). Dilated tubules form intersaccular connecting regions which joint together saccules at the same or different levels between adjacent stacks. Wells exist as large perforations in register with the four cis-most saccules and serve as areas of vesicular interactions. TGNs are variable and can appear to peel off the stack or to be detached from it in the form of an anastomotic tubular network with pale dilated areas corresponding to prosecretory granules connected by short narrow bridges. Elongated or discoid dilated cisternae of endoplasmic reticulum (ER) (sparsely granulated) lie over the cis face of the stack, from which they are separated by an intermediate compartment filled with vesicles and tubules. The ER is also closely juxtaposed to the TGNs and the eighth saccule but interconnections are never seen between them. Vesicles of the COP variety reside at all levels of the stack and appear to bud off the cis-located ER and the edges of the saccules, while clathrin-coated vesicles appear mainly on the trans face of the stack and next to lysosomes. In the supranuclear cytoplasm, clusters of vesicles and tubules, at times budding off enveloping ER, appear to radiate toward the Golgi stacks where they fuse with cis Golgi elements. Taken together, these observations suggest dynamic functions and interactions for the various Golgi elements, associated vesicles, ER, and vesicular tubular clusters. Accepted: 29 January 1998     

Arbuscular mycorrhizal structure and fungi associated with mosses

We investigated the colonization and diversity of arbuscular mycorrhizal (AM) fungi associated with 24 moss species belonging to 16 families in China. AM fungal structures, i.e. spores, vesicles, hyphal coils (including intracellular hyphae), or intercellular nonseptate hyphae, were found in 21 moss species. AM fungal structures (vesicles, hyphal coils, and intercellular nonseptate hyphae) were present in tissues of 14 moss species, and spores and nonseptate hyphae on the surface of gametophytes occurred in 15 species. AM fungal structures were present in 11 of the 12 saxicolous moss species and in six of the ten terricolous moss species, but absent in two epixylous moss species. AM fungal structures were only observed in moss stem and leaf tissues, but not in rhizoids. A total of 15 AM fungal taxa were isolated based on trap culture with clover, using 13 moss species as inocula. Of these AM fungi, 11 belonged to Glomus, two to Acaulospora, one to Gigaspora, and one to Paraglomus. Our results suggest that AM fungal structures commonly occur in most mosses and that diverse AM fungi, particularly Glomus species, are associated with mosses.     

On the presence of inside-out plasma membrane vesicles and vanadate-inhibited K+,Mg2+-ATPase in microsomal fractions from wheat and maize roots

We have estimated the amount of inside-out plasma membrane (PM) vesicles in microsomal fractions from wheat (Triticum aestivum L. cv. Drabant) and maize (Zea mays L.) roots; non-latent activities of the PM markers vanadate-inhibited K⁺, Mg²⁺-ATPase (ΔVO₄-ATPase) and glucan synthase II (GS II, EC 2.4.1.34) were used as markers for inside-out PM vesicles, latent activities as markers for right-side-out PM vesicles, and specific staining with silicotungstic acid (STA) as a general marker for the PM. Separation of presumptive inside-out PM vesicles from right-side-out ones was achieved by counter-current-distribution (CCD) in an aqueous polymer two-phase system. Most of the GS II activity was latent and was found in material partitioning into the upper phase; a distribution which correlated well with that of STA-stained vesicles. Thus, most of the PM vesicles had a right-side-out orientation. ΔVO₄-ATPase, on the other hand, had a dual distribution (particularly pronounced in wheat) and was recovered both in material partitioning into the lower phase and into the upper phase. This indicates that ΔVO₄-ATPase activity was present also in membranes other than the PM. Additional evidence for this interpretation came from sucrose gradient centrifugation of wheat root material. This produced two peaks of ΔVO₄-ATPase activity with the membranes partitioning into the lower phase, none of which coincided with the peak obtained with right-side-out PM vesicles. Taken together, these results indicate that only very few inside-out PM vesicles are present in the microsomal fraction, and that ΔVO₄-ATPase as a marker for the PM, in contrast to GS II, may give quite misleading results with some plant materials. This stresses the need to use well-defined preparations of scaled, inside-out PM vesicles in solute uptake studies. The distribution of Ca²⁺-inhibited ATPase, on the other hand, agreed well with those of GS II and STA-stained vesicles both after CCD and sucrose gradient centrifugation, which suggests that Ca²⁺ inhibition may be a more specific property of the PM H⁺-ATPase than vanadate inhibition.     

Different nematocytes have different synapses in the sea anemone Aiptasia pallida (Cnidaria,Anthozoa)

Sea anemones feed by discharging nematocysts into their prey, but the pathway for control of nematocyst discharge is unknown. The purpose of this study was to investigate the ultrastructural evidence of neuro-nematocyte synapses and to determine the types of synaptic vesicles present at different kinds of nematocyst-containing cells. The tip and middle of tentacles from small specimens of Aiptasia pallida were prepared for electron microscopy and serial micrographs were examined. We found clear vesicles in synapses on mastigophore-containing nematocytes and dense-cored vesicles in synapses on basitrich-containing nematocytes and on one cnidoblast with a developing nematocyst. In addition, we found reciprocal neuro-neuronal and sequential neuro-neuro-nematocyte synapses in which dense-cored vesicles were present. It was concluded that : (1) neuro-nematocyte synapses are present in sea anemones, (2) different kinds of synaptic vesicles are present at cells containing different types of nematocysts, (3) synapses are present on cnidoblasts before the developing nematocyst can be identified and these synapses may have a trophic influence on nematocyst differentiation, and (4) both reciprocal and sequential synapses are present at the nematocyte, suggesting a complex pathway for neural control of nematocyst discharge. J. Morphol. 238:53–62, 1998. © 1998 Wiley-Liss, Inc.