Flattened Sacs Research Articles

MoSey1 regulates the unfolded protein response, appressorium development, and pathogenicity of Magnaporthe oryzae

Endoplasmic reticulum (ER) is an enclosed three-dimensional eukaryotic membrane network composed of flattened sacs. Fusion of homologous membranes to the ER membrane is essential for the maintenance of this network structure. In yeast, ER membrane fusion is mediated by Sey1p, whose paralogues function distinctly in different species. In this study, we investigated the biological functions of MoSEY1 in the devastating rice blast fungus Magnaporthe oryzae by functional genomic approach. Compared to wild type, deletion of MoSEY1 considerably decreased the growth and conidia production of M. oryzae. Additionally, the absence of MoSEY1 delayed appressorium formation and invasive hyphae growth. The appressorium function was also impaired in ΔMosey1 mutant. Subcellular localization analysis revealed that MoSey1 is localized at the ER. The ΔMosey1 mutant showed augmented sensitivity to ER stress. Additionally, we found that MoSey1 regulated the unfolded protein response, autophagy, and protein secretion in M. oryzae. In conclusion, our study unveiled the involvement of MoSey1 in the development, pathogenesis, and ER functions in M. oryzae.

Ultrastructural Studies on the Thyroid Gland of Dromedary Camel (Camelus dromedarius)

Background: The previously reported information on the ultrastructure of the thyroid gland of the camel is meager as compared to other domestic animals; thus, the present study was designed to provide the ultrastructural features of the thyroid gland in the camel. Methods: The thyroid glands were collected from naturally died sixteen camels (n=16) of both sexes from Veterinary Clinical Complex, RAJUVAS, Bikaner, Rajasthan. The transmission electron microscopy (TEM) of the thyroid gland was done at Sophisticated Analytical Instrumental Facility (SAIF), Department of Anatomy, All India Institute of Medical Sciences, New Delhi. The standard protocol of AIIMS, New Delhi, was followed for electron microscopy. Result: The thyroid gland of the camel consisted of thyroid follicles comprised of cuboidal thyroid follicular cells. The follicular cells contained a nucleus with heterochromatin concentrated marginally on the nuclear membrane and the euchromatin was well dispersed in the nucleus with well-marked nucleoli. The nucleus of the follicular cell was rounded. The apical regions of the plasma membrane in follicular cells consisted of microvilli, which were numerous, thinner and finger-like in outline. The mitochondria appeared as round, oval, rod-shaped and dumbbell-shaped. The rough endoplasmic reticulum was visible as elongated, irregular, elliptical cisterns. The Golgi complex was well marked and consisted of flattened sacs, vacuoles and small vesicles. The parafollicular cells were found in small numbers and positioned basally between two follicular cells, close to the basement membrane. It can be concluded that the ultrastructure of the thyroid gland of the camel does not differ from that of other mammalian species.

Vacuole Biogenesis in Plants: How Many Vacuoles, How Many Models?

Vacuoles are the largest membrane-bounded organelles and have essential roles in plant growth and development, but several important questions on the biogenesis and dynamics of lytic vacuoles (LVs) remain. Here, we summarize and discuss recent research and models of vacuole formation, and propose, with testable hypotheses, that besides inherited vacuoles, plant cells can also synthesize LVs de novo from multiple organelles and routes in response to growth and development or external factors. Therefore, LVs may be further classified into different subgroups and/or populations with different pH, cargos, and functions, among which multivesicular body (MVB)-derived small vacuoles are the main source for central vacuole formation in arabidopsis root cortical cells.

Cell type-specific responses to wingless, hedgehog and decapentaplegic are essential for patterning early eye-antenna disc in Drosophila.

The Drosophila eye-antenna imaginal disc (ead) is a flattened sac of two-layered epithelia, from which most head structures are derived. Secreted morphogens like Wingless (Wg), Hedgehog (Hh), and Decapentaplegic (Dpp) are important for early patterning of ead, but the underlying mechanisms are still largely unknown. To understand how these morphogens function in the ead of early larval stages, we used wg-LacZ and dpp-Gal4 markers for the examination of wild-type and mutant eads. We found that the ead immediately after hatching was crescent-shaped with the Bolwig’s nerve at the ventral edge, suggesting that it consists of dorsal domain. In a subsequent step, transcriptional induction of dpp in the cells along the Bolwig’s nerve was followed by rapid growth of the ventral domain. Both Wg and Hh were required for the formation of the ventral domain. Wg was crucial for the growth of the entire ead, but Hh was essential for cell division only in the dorsal domain. In the ventral domain, Hh regulated dpp transcription. Based on these data, we propose that signaling among distinct groups of cells expressing Wg, Dpp, or Hh in the ead of the first-instar larvae are critical for coordinated growth and patterning of ead.

Tracking Single Serotonin Transporter Molecules at the Endoplasmic Reticulum and Plasma Membrane

Transmembrane proteins are synthesized and folded in the endoplasmic reticulum (ER), an interconnected network of flattened sacs or tubes. Up to now, this organelle has eluded a detailed analysis of the dynamics of its constituents, mainly due to the complex three-dimensional morphology within the cellular cytosol, which precluded high-resolution, single-molecule microscopy approaches. Recent evidences, however, pointed out that there are multiple interaction sites between ER and the plasma membrane, rendering total internal reflection microscopy of plasma membrane proximal ER regions feasible. Here we used single-molecule fluorescence microscopy to study the diffusion of the human serotonin transporter at the ER and the plasma membrane. We exploited the single-molecule trajectories to map out the structure of the ER close to the plasma membrane at subdiffractive resolution. Furthermore, our study provides a comparative picture of the diffusional behavior in both environments. Under unperturbed conditions, the majority of proteins showed similar mobility in the two compartments; at the ER, however, we found an additional 15% fraction of molecules moving with 25-fold faster mobility. Upon degradation of the actin skeleton, the diffusional behavior in the plasma membrane was strongly influenced, whereas it remained unchanged in the ER.

Differentiation of the epipod chloride cells in the limb of Artemia

Summary The epipod forms at instar V as a sac of epidermal cells extending from the dorsal edge of the thoracopod. Pillar processes from the basal surface of the cells connect opposing epithelia across the hemocoel of the flattened sac. Differentiation started in late premolt of instar VIII and by instar IX all the cells had increased in height, greatly enhanced the surface area of the plasma membrane, and increased the number of mitochondria. Chloride transport (silver staining) followed the same temporal pattern demonstrating that differentiation of chloride cell morphology and transport function was attained during a period of one instar. The presence of mitotic figures revealed that the chloride cells retained the ability to replicate after differentiation.

Cytoskeleton Structure and Composition in Choanoflagellates

The structure and composition of the cytoskeleton has been studied in Monosiga ovata (Protozoa: Order Choanofiagellida Kent 1880) using a combination of methods in association with light and electron microscopy. Supplementary observations are included for Desmarella moniliformis. The basal body of the single anterior flagellum is subtended proximally and at right angles by a second, non‐flagellar basal body. The edges of the two basal bodies are connected by a fibrillar bridge. A long, narrow, striated, fibrillar rootlet extends posteriorly from the lower edge of the non‐flagellar basal body towards the Golgi apparatus. It is associated throughout most of its length with the surface of a flattened sac. Rootlet microtubules pass radially from a ring of electron dense material which encircles the distal end of the flagellar basal body. These microtubules extend outwards for about one‐third of the length of the cell. Within each collar tentacle is a longitudinal bundle of microfilaments composed of actin as illustrated by rhodamine‐phalloidin staining for fluorescence microscopy. The base of each microfilament bundle is associated with one or more rootlet microtubules by fine fibrillar bridges. The attachment between microtubules and tentacle microfilaments is further demonstrated by their coordinated displacement when the cytoskeleton becomes dislodged. The role of the cytoskeleton in maintaining the position of the collar tentacles during interphase and cell division is discussed.

Epidermal derivatives as xylem elements and transfer cells: a study of the host-parasite interface in two species of Triphysaria (Scrophulariaceae)

Haustoria ofTriphysaria pusilla andT. versicolor subsp.faucibarbata from a natural habitat were analysed by light and electron microscopy. The keel-shaped edge of the secondary haustorium generally splits the epidermis and cortex of the host root parallel to the root axis, and penetrates to the host vascular tissue. Anticlinally elongated epidermal cells of the haustorium constitute most of the host/parasite interface. Some of these epidermal cells are divided by oblique cell walls. Some of their oblique daughter cells as well as some undivided epidermal cells differentiate into xylem elements. Single epidermal cells occasionally intrude into the vascular tissue of the host and individual host cells can be invaded. The surface area of the plasmalemma in parasitic parenchymatous interface cells is increased by the differentiation of wall labyrinths characteristic of transfer cells and by the development of membrane-lined cytoplasmic tubules or flattened sacs which become embedded in the partly lignified interface cell-wall. Mycorrhizal fungal hyphae enter the xylem bridge in some haustoria. Implications of these observations for the function of the haustorium are discussed.

Architecture of butterfly scales: Pattern formation by single cells

Scales, the fine “dust” that covers the wings and bodies of butterflies and moths, are extremely complex in form. Like the wings and the rest of the exoskeleton they are made of non-living cuticle. Each is the product of a single cell and as such represents pattern formation on a microscopic level, all the more remarkable in view of the great variety in forms that scales may take.On the wing, the scales are usually arranged in rows of alternating long cover scales and shorter ground scales (Figure 1). The ground scales are usually unspecialized and show typical scale architecture: each is essentially a flattened sac whose lower lamina (the surface hidden from view) is smooth and featureless, while the visible upper lamina is elaborated into a gridwork of parallel longitudinal ridges joined at intervals by transverse crossribs (Figure 2). Ridges and ribs together frame rows of windows that open into the interior of the scale. The interior is usually empty except for pillar-like trabeculae which join the upper and lower laminae.

Molecular aspects of plastid envelope biochemistry

One of the most characteristic features of a plant cell is the existence of plastids representing a whole family of interrelated organelles [1, 2]. Meristematic cells contain small undifferentiated plastids or proplastids, which have little internal structure apart from a few flattened sacs which occasionally have continuity with the inner envelope. They ensure the continuance of plastids within a species from generation to generation and are capable of considerable structural and metabolic transformations which give rise to more mature plastids. During root cell differentiation, proplastids develop mostly into amyloplasts, which are storage plastids containing large starch grains. During leaf cell differentiation in the presence of light, proplastids develop into chloroplasts, which are the site of photosynthesis, but in the absence of light, they develop into etioplasts, containing a crystal-like structure called the prolamellar body. Etioplasts can then be transformed into chloroplasts upon illumination. Carotenoid-rich plastids, or chromoplasts, can develop from proplastids or chloroplasts during flower development, fruit ripening or senescence. Therefore, plastid differentiation within plant cells is both light- and tissue-specific, and mechanisms should exist that control nuclear and plastid gene expression.

Three-dimensional electron microscopy of the sarcoplasmic reticulum and T-system in embryonic chick skeletal muscle cells in vitro

The formation of the sarcoplasmic reticulum (SR) and the transverse tubular system (T-system) in embryonic chick skeletal muscle cells in vitro was studied by either the critical point drying-physical rupturing or physical rupturing-freeze drying together with rotary shadowing. In these cells, two membranous systems were observed. One was composed of flattened sacs which were either isolated or were connected to each other with slender processes to form mostly longitudinally oriented strands. Initially, these sacs had small granules at their surface and were found mainly under the sarcolemma. Later, they became smooth at their surface, extending throughout the cytoplasm to form irregular and dense networks. At later phases, the networks tended to be disposed at right angle to nascent myofibrils, exhibiting a characteristic honeycomb appearance. From the similarities in thin section images, they were identified as developing SR.

CYTOCHEMICAL STUDY OF ELECTRON MICROSCOPY ON FRUCTOSE 1,6-DIPHOSPHATASE AND URIDINE DIPHOS PHOGLUCOSE PYROPHOSPHORYLASE IN THE MESO PHYLL CELLS OF Stevia rebaudiana BERTONI

The subcellular localizations of fructose 1,6-diphosphatase (FDPase, EC 3.1.3.11) and uridine diphos- phoglucose pyrophosphorylase (UDPG PPlase, UTP:α-D-glucose-I-phosphate uridylytransferase, EC 2.7. 7.9) in the mesophyll cells of a new sweetener plant (Stevia rebaudiana Bertoni), both of which are critical in carbohydrate metabolism, were determined and the activities of both enzymes in the leaves of different ages were compared in this study. This experiment reveals: FDPase is a membrane-bound enzyme and is specifically localized on the thylakoid membranes of chloroplasts and the plasmic membranes. FDPase is only found on the thylakoid membranes of chloroplasts in the young mesophyll cells, while it is found on both the thylakoid membranes of chloroplasts and the plasmic membranes in the mature meso- phyll cells. UDPG PPlase is distributed in the cytoplasmic matrix freely, and is localized on Golgi flat- tened sacs and Colgi vesicles in a membrane-bound form. In this study, it is suggested that the chloroplasts, the cytoplasmic matrix and Golgi complex are important in the synthesis of stevioside.

Fine-structural and morphometrical studies on the segmental septa of the giant fibers in the earthworm, Eisenia foetida

The fine structure of junctional specializations on the segmental septa in the median and lateral giant fibers of the earthworm (Eisenia foetida) was examined. Eight morphologically different septal domains were identified; a gap junction, a junction with hemispherical hollow structures, a chemical synapse-like junction, intermediate type and punctum adherens type junctions, a junction with adjoining vesicular layers, an area flanked by flattened membranous sacs, a non specialized area, and an area consisting of widely separated membranes with interposed glial processes. The area of each domain was measured by a cytometrical technique using quasi-serial sections. The gap junction occupied 3% and 0.2% of the septal area of the median and lateral giant fibers, respectively. Junctions with hemisperical hollow structures, characteristic of the earthworm giant fibers, occupied 2.5% and 13.9% of the median and lateral giant fibers, respectively. Various membrane domains except the gap junction, the junction with hemispherical hollow structures, and the chemical synapse-like junction accounted for similar proportional areas in both median and lateral giant fibers. The functional implications of these junctional specializations, especially the gap junction, are discussed.

Genèse des différents organites de la spore uninucléée d’ Amblyospora culicis (Protozoa, Microspora)

The elaboration of the uninucleate spore of Amblyospora culicis (Protozoa, Microspora) is described by transmission electron microscopy. The first event of this sporogenesis is the formation of the spore wall. Some metabolic granules elaborated in the pansporoblastic vacuole fuse and set as a wall on the outside of the sporont plasma membrane. This wall appeared as two electron dense layers separated by a transparent one. During sporogenesis this wall thickens and becomes complex. In the mature spore, it is composed of an inner electron transparent endospore and an outer exospore exhibiting 5 structurally different layers. The polar filament is elaborated in the sporoblast. It is firstly a coil in the posterior half of the sporoblast; then its anterior end moves to reach a granular body which appeared in the anterior part of the sporoblast. This granular body elaborates the polar cap and becomes the polar sac. The last organelle differentiated is the polaroblast. It is elaborated from an amorphous structure which appeared under the polar sac of the young spore. In this structure numerous membranous cisternae appear. The first become parallel and flattened sacs, while the last stay swollen vesicles. When the sporogenesis is over, the spore possesses a thick wall, an abruptly constricted polar filament and a large polaroplast consisting of membranous flattened sacs and swollen vesicles.

Phototransduction in vertebrate rods.

Rods elaborate a special organelle for converting light into an electrical signal. Their outer segment contains a long stack of flattened sacs, or discs, covered by the plasmalemma. Embedded in the disc membrane are rhodopsin mole­ cules; within the plasmalemma are channels that allow the entry of Na ions during darkness. The absorption of light by rhodopsin initiates a series of events that cross the cytoplasm and stop the plasmalemmal current. Recent studies have revealed the first biochemical steps initiated by light, properties of the plasmalemmal current, and tantalizing bits concerning how the early steps are connected to the subsequent closure of membrane channels. Accord­ ingly, I have divided this review into four parts: (a) properties of the plas­ malemmal current, (b) the early events produced by light, (c) observations that place restrictions on how light controls the current, and (d) a speculative synthesis. Both Ca and cGMp· have been suggested to have an important role in transduction. In one scheme, Ca is stored within discs and is released by light to diffuse across the cytoplasmic space and to block channels (Hagins 1972). In another scheme, cGMP keeps channels open and light activates a phospho­ diesterase that reduces cGMP concentration (see review by Hubbell & Bownds 1979). These two ideas dominate the transduction landscape. Their shadow is seen in every part of the discussion.

Activation of the contractile system in crustacean muscle: Ultrastructural evidence for the role of the T system

Freeze-fracture and thin sections of lobster abdominal fast flexor muscle were used to study the morphology of the sarcoplasmic reticulum (SR) and T system of crustacean muscle. Tannic acid mordanting, which can result in a dense black deposit in the T system lumen, was used to distinguish T system from SR membranes. Ferritin was also used as an extracellular tracer to confirm the tannic acid method. The T system consists of an extensive network of flattened sacs which fills most of the space between the mycfibrils and is in close contact with them. The SR also appears as flattened sacs, sometimes with fenestrations. There is extensive junctional contact between the SR and T system. Quantitative estimates of the volume and surface area of the membranes show that the T system has about 50 % more surface area than the SR. The intramembrane particle (IMP) density of the PF face of the T system is about 1100/ μm 2 membrane, while the IMP density of the PF face of the SR is about 4800/ μm 2 membrane. In morphology, extent, and IMP density, the T system of lobster abdominal fast flexor muscle appears (AFF) adapted to provide at least part of the Ca 2+ for muscle activation and the transport system for relaxation.

Effect of cell density and senescence of WI-38 cells on cytochemically demonstrable phosphatases

Exponentially growing and stationary phase young and old cultures of the human cell line WI-38 were studied using cytochemistry at the ultrastructural level. 5′-Nucleotidase activity was present in the plasma membrane of all cells examined; in exponentially growing cultures the reaction was more intense in mitotic cells than in interphase cells. An increase in the amount of the reaction product was observed at confluency, especially in older cells. The reaction for Mg 2+-activated adenosine 5′-triphosphatase was absent or very weak in exponentially growing cells and increased at confluency, especially in older cells. Alkaline phosphatase was detectable only in the cell membranes and intercellular spaces of young cells at confluency. Acid phosphatase activity was increased in old cells, especially at confluency. In these old cells, positive reactions appeared in numerous small lysosomes, autophagic vacuoles and in some flattened sacs of the Golgi apparatus. The obtained results confirm and extend previous biochemical observations and indicate that changes in phosphatase activity are associated with proliferative activity and senescence of cells growing in vitro.

Adenylate cyclase system of human skeletal muscle: Subcellular distribution and general properties

The subcellular localization of adenylate cyclase was examined in human skeletal muscle. Three major subcellular membrane fractions, plasmalemma, sarcoplasmic reticulum and mitochondria, were characterized by membrane-marker biochemical studies, by dodecyl sulfate polycrylamide gel electrophoresis and by electron microscopy. About 60% of the adenylate cyclase of the homogenate was found in the plasmalemmal fraction and 10–14% in the sarcoplasmic reticulum and mitochondria. When the plasmalemmal preparation was subjected to discontinuous sucrose gradients, the distribution of adenylate cyclase in different subfractions closely paralleled that of (Na + + K +)-ATPase. The highest specific activity was found in a fraction which setteled at the 0.6–0.8 M sucrose interface. The electron microscopic study of this fraction revealed the presence of flattened sacs of variable sizes and was devoid of mitochondrial and myofibrillar material. The electron microscopy of each fraction supported the biochemical studies with enzyme markers. The three major membrane fractions also contained a low K m phosphodiesterase activity, the highest specific activity being associated with sarcoplasmic reticulum. The plasmalemmal adenylate cyclase was more sensitive to catecholamine stimulation than that associated with sarcoplasmic reticulum or mitochondria. The catecholamine-sensitive, but not the basal, enzyme was further stimulated by GTP. The plasmalemmal adenylate cyclase had typical Michaelis-Menten kinetics with respect to ATP and the apparent K m for ATP was approx. 0.3. mM. The pH optimum for that enzyme was 7.5. The enzyme required Mg 2+, and the concentration to achieve half-maximal stimulation was approx. 3 mM. Higher concentrations of Mg 2+ (about 10 mM) were inhibitory. Solubilization of the plasmalemmal membrane fraction with Lubrol-PX resulted in preferential extraction of 106 000- and 40 000-dalton protein components. The solubilized adenylate cyclase lost its sensitivity for catecholamine stimulation, and the extent of fluoride stimulation was reduced to one-sixth of that of the intact membranes. It is concluded that the catalytically active and hormone-sensitive adenylate cyclase is predominantly localized in the surface membranes of the cells within skeletal muscle. (That “plasmalemmal” fraction is considered likely to contain, in addition to plasmalemma of muscle cells, plasmalemma of bloodvessel cells (endothelium, and perhaps smooth muscle) which may be responsible for a certain amount of the adenylate cyclase activity and other propertiesobserved in that fraction.) The method of preparation used in this study provides a convenient material for evaluating the catecholamine-adenylate cyclase interactions in human skeletal muscle.

Cell wall structure and deposition in Glaucocystis.

Events leading to cell wall formation in the ellipsoidal unicellular alga Glaucocystis are described. The wall is deposited in three phases: (a) a thin nonfibrillar layer, (b) cellulosic microfibrils arranged in helically crossed polylamellate fashion, and (c) matrix substances. At poles of cells, microfibrils do not terminate but pass around three equilaterally arranged points, resulting in microfibril continuity between the twelve helically wound wall layers. These findings were demonstrated in walls of both mother cells and freeze-fractured growing cells, and models of the wall structure are presented. Cellular extension results in spreading apart, and in rupture, of microfibrils. On freeze-fractured plasma membranes, there were 35 nm X 550 nm structures associated with the ends of microfibrils. These are interpreted as representing microfibril-synthesizing centers (terminal complexes) in transit upon the membrane. These terminal complexes are localized in a zone, or zones. The plasma membrane is subtended by flattened sacs, termed shields, which become cross-linked to the plasma membrane after completion of wall deposition. During wall deposition, microtubules lie beneath the shields, and polarized filaments lie between shields and plasma membrane. The significance of these findings in relation to understanding the process of cellulose deposition is discussed, and comparisons are made with the alga Oocystis.

Myocardial couplings: Their structural variations in the mouse

In mouse myocardial cells, the sarcoplasmic reticulum (SR) forms specialized complexes (“couplings”) with both the sarcolemma and its extension, the system of transverse (T) and axial (Ax) tubules. As well as contributing to conventional “diads” and “triads,” the junctional region of the SR (J-SR) often forms complexes having special configurations, the latter including: (1) couplings in which J-SR is wrapped partially or completely around T-Ax tubules; (2) “reversed triads” in which a single J-SR saccule is flanked by two T-Ax tubules; (3) “pentad” and “sextad” couplings with multiple J-SR and T-Ax elements; and (4) “bidirectional peripheral couplings” in which J-SR is sandwiched between closely apposed folds of the sarcolemma, a condition frequently observed in the region of the intercalated disc. In the last three configurations, electron-opaque junctional processes are formed on both sides of the flattened sac of J-SR, rather than on a single side as in conventional couplings.