Tridimensional structure of the Golgi apparatus in type A ganglion cells of the rat

Role of Nanoparticle-Conjugates and Nanotheranostics in Abrogating Oxidative Stress and Ameliorating Neuroinflammation

Oxidative stress is a deteriorating condition that arises due to an imbalance between the reactive oxygen species and the antioxidant system or defense of the body. The key reasons for the development of such conditions are malfunctioning of various cell organelles, such as mitochondria, endoplasmic reticulum, and Golgi complex, as well as physical and mental disturbances. The nervous system has a relatively high utilization of oxygen, thus making it particularly vulnerable to oxidative stress, which eventually leads to neuronal atrophy and death. This advances the development of neuroinflammation and neurodegeneration-associated disorders such as Alzheimer's disease, Parkinson's disease, epilepsy, dementia, and other memory disorders. It is imperative to treat such conditions as early as possible before they worsen and progress to irreversible damage. Oxidative damage can be negated by two mechanisms: improving the cellular defense system or providing exogenous antioxidants. Natural antioxidants can normally handle such oxidative stress, but they have limited efficacy. The valuable features of nanoparticles and/or nanomaterials, in combination with antioxidant features, offer innovative nanotheranostic tools as potential therapeutic modalities. Hence, this review aims to represent novel therapeutic approaches like utilizing nanoparticles with antioxidant properties and nanotheranostics as delivery systems for potential therapeutic applications in various neuroinflammation- and neurodegeneration-associated disease conditions.

Three-dimensional reconstruction of the Golgi apparatus in osteoclasts by a combination of NADPase cytochemistry and serial section scanning electron microscopy

The three-dimensional morphology of the Golgi apparatus in osteoclasts was investigated by computer-aided reconstruction. Rat femora were treated for nicotinamide adenine dinucleotide phosphatase (NADPase) cytochemistry, and light microscopy was used to select several osteoclasts in serial semi-thin sections to investigate the Golgi apparatus by backscattered electron-mode scanning electron microscopy. Lace-like structures with strong backscattered electron signals were observed around the nuclei. These structures, observed within the Golgi apparatus, were attributed to the reaction products (i.e., lead precipitates) of NADPase cytochemistry. Features on the images corresponding to the Golgi apparatus, nuclei, and ruffled border were manually traced and three-dimensionally reconstructed using ImageJ/Fiji (an open-source image processing package). In the reconstructed model, the Golgi apparatus formed an almost-continuous structure with a basket-like configuration, which surrounded all the nuclei and also partitioned them. This peculiar three-dimensional morphology of the Golgi apparatus was discovered for the first time in this study. On the basis of the location of the cis- and trans-sides of the Golgi apparatus and the reported results of previous studies, we postulated that the nuclear membrane synthesized specific proteins in the osteoclasts and, accordingly, the Golgi apparatus accumulated around the nuclei as a receptacle.

Three-dimensional morphology of the Golgi apparatus in osteoclasts: NADPase and arylsulfatase cytochemistry, and scanning electron microscopy using osmium maceration

This study was designed to observe osteoclasts in the rat femora by light and electron microscopic cytochemistry for nicotinamide adenine dinucleotide phosphatase (NADPase) and arylsulfatase, and scanning electron microscopy using osmium maceration to assess the three-dimensional morphology of the Golgi apparatus in osteoclasts. The Golgi apparatus showed strong NADPase activity and surrounded each nucleus with the cis-side facing the nucleus. The Golgi apparatus could be often traced for a length of 20 μm or longer. Observations of serial semi-thin sections confirmed that a single line of reaction products (=lead precipitates) intervened somewhere between any two neighboring nuclei. The nuclear membrane showed strong arylsulfatase activity as well as rough endoplasmic reticulum and lysosomes. Scanning electron microscopy showed that the Golgi apparatus covered the nucleus in a porous sheet-like configuration. Under magnification, the cis-most saccule showed a sieve-like configuration with fine fenestrations. The saccules decreased fenestration numbers toward the trans-side and displayed a more plate-like appearance. The above findings indicate the following. (1) The Golgi saccules of osteoclasts have a three-dimensional structure comparable with that generally seen in other cell types. (2) The Golgi apparatus forms a porous multi-spherical structure around nuclei. Within the structure, in most cases a Golgi stack partitions the room into several compartments in each of which a nucleus fits. (3) The nuclear membrane synthesizes some kinds of proteins more stably and sufficiently than the rough endoplasmic reticulum. Consequently, the Golgi apparatus accumulates around nuclei with the cis-side facing the nucleus.

Golgi Fragmentation in Neurodegenerative Diseases: Is There a Common Cause?

In most mammalian cells, the Golgi complex forms a continuous ribbon. In neurodegenerative diseases, the Golgi ribbon of a specific group of neurons is typically broken into isolated elements, a very early event which happens before clinical and other pathological symptoms become evident. It is not known whether this phenomenon is caused by mechanisms associated with cell death or if, conversely, it triggers apoptosis. When the phenomenon was studied in diseases such as Parkinson’s and Alzheimer’s or amyotrophic lateral sclerosis, it was attributed to a variety of causes, including the presence of cytoplasmatic protein aggregates, malfunctioning of intracellular traffic and/or alterations in the cytoskeleton. In the present review, we summarize the current findings related to these and other neurodegenerative diseases and try to search for clues on putative common causes.

Actin acting at the Golgi

The organization, assembly and remodeling of the actin cytoskeleton provide force and tracks for a variety of (endo)membrane-associated events such as membrane trafficking. This review illustrates in different cellular models how actin and many of its numerous binding and regulatory proteins (actin and co-workers) participate in the structural organization of the Golgi apparatus and in trafficking-associated processes such as sorting, biogenesis and motion of Golgi-derived transport carriers.

Architecture of the mammalian Golgi

Since its first visualization in 1898, the Golgi has been a topic of intense morphological research. A typical mammalian Golgi consists of a pile of stapled cisternae, the Golgi stack, which is a key station for modification of newly synthesized proteins and lipids. Distinct stacks are interconnected by tubules to form the Golgi ribbon. At the entrance site of the Golgi, the cis-Golgi, vesicular tubular clusters (VTCs) form the intermediate between the endoplasmic reticulum and the Golgi stack. At the exit site of the Golgi, the trans-Golgi, the trans-Golgi network (TGN) is the major site of sorting proteins to distinct cellular locations. Golgi functioning can only be understood in light of its complex architecture, as was revealed by a range of distinct electron microscopy (EM) approaches. In this article, a general concept of mammalian Golgi architecture, including VTCs and the TGN, is described.

Three-dimensional ultrastructure of the Golgi apparatus in different cells: high-resolution scanning electron microscopy of osmium-macerated tissues

The three-dimensional ultrastructure of the Golgi apparatus in different cells of the rat - epithelial principal cells in the epididymal duct, goblet cells in the jejunum, gonadotrophs in the pituitary gland and dorsal root ganglion cells - was studied by scanning electron microscopy (SEM) of osmium-macerated tissues. The Golgi apparatus in the epididymal principal cells took the shape of a candle flame with irregular-shaped cisterns, while those in the goblet cells of the jejunum were cup-shaped or cylindrical with flat cisterns. Gonadotrophs had a large spherical Golgi apparatus; this apparatus was composed of several concentric cisterns with large round windows through which the rough endoplasmic reticulum (rER) and mitochondria extended into the center of the globular Golgi apparatus. Dorsal root ganglion cells had several small Golgi stacks scattered in the cytoplasm. In all Golgi apparatuses of the different cells examined in the present study, the cis-most cistern was generally composed of a flattened sheet with numerous small fenestrations on its wall. On the other hand, the shape of the trans-most cistern varied by cell type; it was generally composed of tubules and/or small sheets which were sometimes connected with each other to form a rather complicated structure. The cis-most cistern and the trans-most cistern were often closely associated with the rER although no direct communication was found between them. These findings indicate that the structure of the Golgi apparatus, especially its overall shape and the ultrastructure of the trans-most cistern, varies by cell type, a point to be considered in relation to the function of the individual cells.

Recycling of the insulin-sensitive glucose transporter GLUT4. Access of surface internalized GLUT4 molecules to the perinuclear storage compartment is mediated by the Phe5-Gln6-Gln7-Ile8 motif

The insulin-sensitive glucose transporter GLUT4 is translocated to the plasma membrane in response to insulin and recycled back to the intracellular store(s) after removal of the hormone. We have used clonal 3T3-L1 fibroblasts and adipocyte-like cells stably expressing wild-type GLUT4 to characterize (a) the intracellular compartment where the bulk of GLUT4 is intracellularly stored and (b) the mechanisms involved in the recycling of endocytosed GLUT4 to the store compartment. Surface internalized GLUT4 is targeted to a large, flat, fenestrated saccular structure resistant to brefeldin A that localized to the vicinity of the Golgi complex is sealed to endocytosed transferrin (GLUT4 storage compartment). Recycling of endocytosed GLUT4 was studied by comparing the cellular distributions of antibody/biotin tagged GLUT4 and GLUT4(Ser(5)), a mutant with the Phe(5)-Gln(6)-Gln(7)-Ile(8) inactivated by the substitution of Ser for Phe(5). Ablation of the Phe(5)-Gln(6)-Gln(7)-Ile(8) inhibits the recycling of endocytosed GLUT4 to the GLUT4 store compartment and results in its transport to late endosomes/lysosomes where it is rapidly degraded.

Three-dimensional visualization of the Golgi apparatus: observation of Brunner's gland cells by a confocal laser scanning microscope

The three-dimensional structure of the Golgi apparatus in cells of the Brunner's gland in the mouse was observed by using a confocal laser scanning microscope. Two lectins, FITC-labeled soybean agglutinin and Texas red-labeled Griffonia simplicifolia agglutinin II, were used to visualize the whole Golgi apparatus. Staining with the former lectin, which has been known to label the cis-stacks, showed a lacy dome-like structure situated in the supranuclear region. Staining with the latter lectin, known to label the intermediate-to-trans-stacks and the secretory granules, showed a dome-like structure consisting of network and cobblestone-like patterns in the same region and also granular stainings near the surface of the cobblestone-like patterns and the apical region of a cell. Double-staining demonstrated that the soybean agglutinin-labeled network always surrounded the G. simplicifolia agglutinin II-stained structure. Based on these observations, we propose a new three-dimensional model of the Golgi apparatus: it forms a dome-like structure over a nucleus, a network of cis-stacks forms its outer boundary, and this outer boundary is lined and paved with successive intermediate and trans-stacks. It is thought that secretory granules are released toward the internal space of the Golgi apparatus and transported to the apical cytoplasm through the holes of the network.

Coordinate assembly of lipids and enzyme proteins into epidermal lamellar bodies

Formation of the epidermal permeability barrier requires delivery of lamellar body (LB) contents to the stratum corneum interstices. LB are enriched in a mixture of polar lipids and a family of hydrolytic enzymes, required for the extracellular processing of the secreted polar lipids into the more hydrophobic products which mediate barrier function. Prior non-quantitative studies show that acute barrier disruption leads to immediate secretion of the contents of performed LB from the outermost layer of granular cells, followed by the synthesis and accelerated secretion of newly-formed (= nascent) organelles over 0.5-4 h. We asked here whether lipids and hydrolytic enzymes are packaged into nascent organelles separately, or in a parallel, linked process. We first quantified the rate of appearance of lipids (by the content of internal lamellae within LB) and enzyme content (by cytochemistry of neutral lipase and acid sphingomyelinase); both are concentrated in LB, and in nascent organelles. Immediately after barrier disruption, the density of LB in the cytosol of the outermost granular cell decreased by > 50% reduction at 30 min, returning to near-normal densities by 4 h. Nascent organelles budded off a trans-Golgi-like reticulum, in the outermost granular cells as early as 30 min. In quantitative studies, LB progressively accumulated lipid and enzyme contents in parallel. However, when lipid/lamellae generation was inhibited with lipid synthesis inhibitors, enzymes did not accumulate in organelles. Likewise, when exogenous physiologic lipids were delivered to sites of LB generation in the face of brefeldin A blockade of organellogenesis, or when lipids were delivered in conjunction with treatment with lipid synthesis inhibitors, enzymes accumulated only in those organelles that displayed lipid content. These studies demonstrate: (a) quantitative changes in the density of LB in the outermost granular cell at various time points after acute barrier disruption; (b) the origin of nascent organelles in a trans-Golgi-like reticulum; (c) co-ordinate packaging of lipid and enzyme contents into nascent organelles; (d) that lipid deposition in nascent organelles is required for enzyme accumulation; and (e) that enzymes can be delivered to nascent organelles, even if the source of lipid is of exogenous rather than endogenous origin.

3D topography of noncompact zone Golgi tubules in rat spermatids: a computer-assisted serial section reconstruction study

BACKGROUND

In the Golgi apparatus, the 3D topography of saccules in the compact zones (CZs) is better understood than that of tubules in the noncompact zones (NCZs). The positioning of NCZ tubules relative to each other and to CZ saccules was studied in rat spermatids by computer-assisted serial section microscopy.

METHODS

Twenty-four (semi) serials (3-6 consecutive sections each) in total were collected from untreated tissues and from tissues treated for glucose-6-phosphatase (G6P) cytochemistry as an alignment tool. The serials proceeded along either the cis-trans or the medial-lateral axes of the Golgi and collectively sampled all portions of this organelle. Selected serials were computer reconstructed and the final models displayed in red-green/red-blue stereo.

RESULTS

In single thin sections, NCZ tubules typically appeared randomly oriented; however, in serial sections a high degree of organization was evident. Most tubules were traceable to the type of tubular networks (TNs) that interconnect equivalent CZ saccules (see review Rambourg and Clermont, 1990) Such TNs were present at consecutive saccular levels through each NCZ, were stacked like the saccules from which they originate, and in many regions were aligned from cis-trans. The cis-most of the TNs projected above the cis-pole of the stacked saccules and were penetrated by coated and uncoated ER buds.

CONCLUSIONS

The function of the extensive NCZ tubular domain, consisting of the stacked and aligned TNs, will have to be addressed in future studies. However, the specific topography of the cis-most TNs make them candidates to serve as acceptor membranes in ER-Golgi transport.

Trans-Golgi network (TGN) of different cell types: three-dimensional structural characteristics and variability

BACKGROUND

The trans-Golgi network (TGN) is generally considered as a distinct and permanent structural compartment of the Golgi apparatus of various cell types. To verify this postulate we examined and compared the three-dimensional characteristics of the TGNs of 14 different mammalian cell types as presented in our various publications since 1979 when we initially described the trans-tubular network of Sertoli cells.

METHODS

In all these studies we used low and high voltage electron microscopes on thin or thick sections of tissues fixed with glutaraldehyde and postfixed with reduced osmium. The sections were stained with uranyl acetate and lead citrate. Stereopairs, prepared from photographs of tilted specimens, permitted a direct observation of the three-dimensional structure of the various elements of the Golgi apparatus.

RESULTS

The TGNs are multilayered and extensive in cells which do not form large typical secretory granules (Sertoli cells, nonciliated cells of ductuli efferentes, spinal ganglion cells) but have an extensive lysosomal system. The TGN is absent in cells forming very large secretory granules (secretory cells of seminal vesicles and lactating mammary glands). The TGNs are small in cells producing small to medium-size secretory granules and/or appear as residual fragments on the trans aspect of the Golgi stacks (e.g., mucous cells of Brunner's gland, pancreatic acinar cells, etc.). In cells with multiple and extensive TGNs, a continuity of these tubular networks with the two or three transmost saccules of the stack is observed but there are seemingly no connections between the TGNs. Whenever the TGNs are present, they do not form a continuous structure along the Golgi ribbon. However, they do present, in all cases, configurations suggestive of desquamation and renewal.

CONCLUSIONS

The structure of the TGN varies considerably from one cell type to another, being extensive in cells not showing typical secretory granules but having an extensive lysosomal system, while in secretory cells showing small or large secretory granules the TGN is either small or even entirely absent.

Changes in the morphology and phosphatase cytochemistry of the Golgi region of hepatocytes during the acute phase response to inflammation

BACKGROUND

During the acute phase response to inflammation, the Golgi apparatus of rat hepatocytes processes an increased quantity of glycoproteins, in the form of acute phase reactants.

METHODS

The compartmental organization of the hepatocyte Golgi of control and 24 hour inflamed rats was studied, using transmission electron microscopic techniques, including cytochemistry, to detect nicotinamide adenine dinucleotide phosphatase (NADPase), thiamine pyrophosphatase (TPPase), and cytidine monophosphatase (CMPase) activity.

RESULTS

In inflamed rats, individual Golgi stacks were enlarged, but retained their organization into four compartments: 1) a phosphatase negative, perforated cis-element, 2) two mid-saccules which sometimes were positive for NADPase, 3) one or occasionally two NADPase and TPPase positive trans-saccules, and 4) a tubulovesicular trans-Golgi network (TGN) which was NADPase reactive and contained a spotty TPPase reaction product. Two of these compartments were noticeably altered in response to inflammation. The two mid-saccules were consistently and uniformly dilated. The TGN was altered to the point of being difficult to recognize and had acquired CMPase reactivity. In control rats the TGN consisted of anastomosing tubules forming cage-like structures; secretory granules containing lipoprotein particles pinched off from these. In inflamed rats, most of the cage-like TGN structures had been replaced with an extensive vesicular syncytium which produced secretory granules with a granulofilamentous content.

CONCLUSIONS

In hepatocytes from inflamed rats an apparent switch had occurred in the type of secretory material processed by the Golgi apparatus. Furthermore, the inflammation-induced increase in the size of individual Golgi stacks apparently was not due to a parallel increase in size of all Golgi saccules. Rather, saccules within given Golgi compartments responded in a characteristic and specific manner to the increase in glycoprotein processing that occurs during inflammation.

Connections between the various elements of the cis- and mid-compartments of the Golgi apparatus of early rat spermatids

BACKGROUND

The exact structural relationships of the saccules, membranous tubules, and vesicles that compose the cis- and mid-compartments of the Golgi cortex of rat spermatids was investigated to determine the relationship of these elements to each other.

METHODS

Tissues fixed with glutaraldehyde and buffered in sodium cacodylate were examined with the electron microscope. Electron micrographs, including stereopairs, were analyzed to determine the three-dimensional organization of the Golgi elements.

RESULTS

The deeper layer of the Golgi cortex was composed of stacks of saccules connected to each other either by saccules or membranous tubules. The peripheral region of the Golgi cortex, located between the cis-side of the stacks and a network of overlying ER cisternae contained numerous membranous tubules and vesicles of two class sizes: 50-100 nm vesicles and microvesicles 5-10 nm in diameter. The tubules formed tight networks, known as cis-elements or cis-Golgi networks (CGN), which were strictly parallel and next to the first or cis-saccule of the stack. The cis-elements were continuous with more loosely arranged peripheral tubules which formed elaborate, intertwined and interconnected networks. These peripheral tubules closely approximated the overlying ER cisternae in areas often showing fuzz-coated finger-like projections. Occasionally such peripheral tubules were continuous with ER cisternae. The saccules forming the stacks were continuous with membranous tubules which not only connected saccules of adjacent stacks, but also saccules of the same stack. These tubules were also connected with the tight tubular networks forming the cis-elements and the broad networks formed by the peripheral membranous tubules. Vesicles (50-100 nm) and microvesicles (5-10 nm) frequently formed aggregates in the peripheral Golgi region next to areas of ER membrane free of fuzz-coated projections. The microvesicles, embedded in a denser cytoplasmic matrix, had a more or less distinct delimiting membrane suggestive of their disintegration in this juxta-ER location. The 50-100 nm vesicles that were seen at the periphery of the vesicular aggregates appeared to form mainly from the membranous tubules of the Golgi cortex.

CONCLUSIONS

Thus the saccules and membranous tubules of the spermatid's Golgi cortex formed a single continuous membraneous system connected to ER cisternae. The vesicles, seemingly arising from the membranous tubules, appear to follow a retrograde pathway and undergo dissolution next to ER cisternae.

Structure of the Golgi apparatus in stimulated and nonstimulated acinar cells of mammary glands of the rat

The structural features of the Golgi apparatus of acinar cells of mammary glands were examined with the electron microscope in 3 groups of rats: (1) in lactating female animals at 8 days postpartum, which served as controls; (2) in female rats sacrificed at various intervals from 2 to 30 hours following separation from their 8-day old pups; and (3) in females separated from their 8-day-old pups for a period of 12 hours and returned to their litters for durations of 1, 2, 4, and 8 hours. In animals of group 2, the Golgi stacks remained identical to that of controls between 2 and 8 hours. At 12 hours and later, the Golgi stacks decreased progressively in size, but the number of elements composing the stacks remained similar to that of lactating females and all contained casein submicelles. At 24 and 30 hours, typical secretory granules containing casein micelles disappeared from the trans aspect of the stacks. The earliest and most striking changes observed in the Golgi apparatus of the rats of group 2 took place at 12 hours. At this time, the prosecretory and secretory granules decreased considerably in volume and lost most of their electron-lucent content. This indicated that the delivery of small molecules, i.e., lactose and H2O, to these structures was soon altered following arrest of the sucking stimulus. In animals of group 3, the size of prosecretory and secretory granules and the amount of their electron-lucent content reverted to normal at 4 hours. Thus the influx of lactose and H2O into these structures appears to be rapidly restored after returning the pups to their mothers. The decrease in size of the Golgi stacks noted at 12, 18, and 24 hours following arrest of lactation (group 2), was accompanied by an increase in number of small vesicles that formed clusters next to the Golgi stacks and in "wells." Thus in these regressing Golgi stacks, many of the associated small vesicles appear to arise by vesiculation of the saccules.

Modulation of the Golgi apparatus in stimulated and nonstimulated prolactin cells of female rats

The three-dimensional structure of the Golgi apparatus and its compartments in prolactin cells has been examined in lactating rats in which secretion of prolactin was suppressed by removing the litter or stimulated by allowing the pups to suckle again. As soon as 2 hr after removal of the litter, large irregular progranules and numerous large pale vesicles accumulated in the trans-Golgi area together with vesicular or tubular fragments. The cis-tubular network was no longer recognizable on the cis-face of the Golgi ribbon; the saccules of the midcompartment were partitioned by narrow fissures and also became perforated in register by numerous fenestrations of various sizes and irregular contours. The concomitant appearance of numerous vesicles in the cavities thus formed as well as in the surrounding cytoplasm indicated that they probably arose by the progressive cavitation and fragmentation of saccules of the mid compartment. Such a process, which reached a maximum between 4 and 6 hr after removal of the litter from the mother, was no longer observed at 8 and 12 hr, at which time intervals the Golgi apparatus was reduced in size with no cis-tubular elements and progranules on its trans-aspect and few vesicles in its surroundings. When mothers, separated from their litters for a period of 12 hr, were returned to their pups for 20 min, the cis-tubular network reappeared on the cis-aspect of the Golgi stacks and presumably formed by fusion of vesicles and anastomosed tubules located next to the cisternae of the rough endoplasmic reticulum. In addition, the structure of the midsaccules returned to the stimulated condition, and early progranules were again segregated within the trans-most saccules of the Golgi stack. Hence, the Golgi apparatus of prolactin cells was rapidly and deeply modified in the presence or absence of stimulation.

Segregation of secretory material in all elements of the Golgi apparatus in principal epithelial cells of the rat seminal vesicle

At the apex of the epithelial principal cells of the seminal vesicle, there appears to be two types of mature secretory granules, i.e., large and small. Both types of secretory granules showed an eccentric electron-dense spherical body with one pole attached to the delimiting membrane. The remainder of the large granule surrounding the eccentric body showed a granulofilamentous texture, whereas that of the small granule was electron lucent. The formation of these two types of granules was traced back to the various elements of the Golgi stacks. In the case of the large granules, the earliest stage of segregation of the precursor of the eccentric dense body was observed in distensions of the cis-element. Within distensions of all subjacent saccules, the dense bodies continued to be present but progressively increased in size while remaining attached to the saccular membrane. Following separation from the trans-face of the stack, the large prosecretory granules continued to increase in size by fusing with each other. The very large prosecretory granules, as they migrated toward the cell apex to become mature secretory granules, reduced in size prior to exocytosis. The small granules formed exclusively on the trans-aspect of the Golgi stacks and did not appear to fuse with each other. Observations on the formation of the large prosecretory granules within the Golgi apparatus and of the eccentric body in particular, which may be taken as a marker of the saccular membrane, were suggestive of a cis-trans migration and renewal of Golgi saccules.

Formation of secretory granules in the Golgi apparatus of prolactin cells in the rat pituitary gland: a stereoscopic study

The mode of secretory granule formation in prolactin cells was analyzed in thin or thick sections of pituitary glands from non-lactating or lactating female as well as from male rats. In all these animals, the Golgi apparatus of prolacting cells consists of a continuous twisted ribbon-like structure that branches and anastomoses to form a hollow sphere located in the juxtanuclear area. The early signs of secretory granule formation are observed along the trans-aspect of the Golgi ribbon where progranules appear as focal distensions simultaneously occurring anywhere in the last trans thiamine pyrophosphatase (TPPase)-containing Golgi element. In the transmost Golgi saccule, such dilatations usually contain several nodular masses of electron opaque material which are separated from each other and from the saccular membrane by a less intensely stained material. While this transmost saccule becomes more fenestrated, its focal polynodular distensions seemingly yield polynodular tubular progranules which are initially closely apposed and usually parallel to the trans face of the Golgi ribbon. Subsequently, these progranules, which frequently show small membranous tubules or tubular networks attached to them, are seen some distance from the Golgi stacks and progressively transform into the more compact polymorphous granules characteristic of prolactin cells. These observations suggest that the polynodular tubular progranules arise by fragmentation of portions of the trans-Golgi elements rather than by fusion of small uninodular granules budding from the edges of a trans-Golgi saccule. Once the progranules have been liberated, the rest of the transmost Golgi element appears to break down into small residual networks, tubules, and vesicles. Thus, in prolactin cells as in other glandular cells, the whole transmost Golgi element would fragment during formation of prosecretory granules.

Three-dimensional structure of cytidine monophosphatase reactive trans-Golgi elements in spinal ganglion cells of the rat

In order to analyse, at the electron microscope level, the three-dimensional configuration of the trans compartment of the Golgi apparatus rat dorsal root ganglia were treated to demonstrate cytidine monophosphatase (CMPase) activity. The localization of enzymatic activity in the Golgi apparatus varied according to cell types. In type A and C cells, CMPase was exclusively located in the transmost sacculotubular element, whereas in type B cells all the saccules of the stacks forming the Golgi ribbon and the trans-Golgi networks were impregnated. Numerous dense bodies seen at proximity were also CMPase positive. In 3 microns thick sections of type A cells examined at low magnification, the impregnated element was scattered throughout the cytoplasm and never formed a continuous structure. In type B cells, the strongly reactive trans-Golgi networks did not follow the entire length of the impregnated Golgi ribbon but were preferentially located in the concavity of its arched portions. At higher magnification and in all cell types some tubular portions of the trans-Golgi networks took the appearance of spheroidal cage-like structures, the CMPase positive anastomotic tubules forming the bars of the cage. Anastomotic tubules separated from the trans-Golgi networks formed fenestrated spheres, while nearby CMPase-reactive dense bodies exhibited a paler hilus. These observations were taken to indicate that in ganglion cells, some CMPase positive dense bodies, presumably lysosomes, formed by fragmentation of the trans-Golgi networks.

Tubular early endosomal networks in AtT20 and other cells

Using horseradish peroxidase (HRP) as a fluid-phase endocytic tracer, we observed through the electron microscope numerous tubular endosomes with a diameter of 30-50 nm and lengths of greater than 2 microns in thick sections (0.2-0.5 microns) of AtT20 cells. These tubular endosomes are multibranching and form local networks but not a single reticulum throughout the cytoplasm. They are sometimes in continuity with vesicular endosomal structures but have not been observed in continuity with AtT20 cell late endosomes. Tubular endosomal networks are not uniformly distributed throughout the cytoplasm, but are particularly abundant in growth cones, in patches below the plasma membrane of the cell body, and surrounding the centrioles and microtubule organizing center (MTOC). Tubular endosomes at all these locations receive HRP within the first 5 min of endocytosis but approximately 30 min of endocytosis are required to load the tubular endosomal networks with HRP so that their full extent can be visualized in the electron microscope. After 10 min of endocytosis, complete unloading occurs within 30 min of chase, but between 30 and 60 min are required to chase out all the tracer from the tubular endosomes loaded to steady state during 60 min endocytosis of 10 mg/ml HRP. In interphase cells, neither the loading nor unloading of tubular endosomes depends on microtubules but in cells blocked in mitosis by depolymerization of the mitotic spindle with nocodazole, HRP does not chase out of tubular endosomes. The thread-like shape of tubular endosomes is not dependent on microtubules. Furthermore, HRP is delivered to AtT20 tubular endosomes at 20 degrees C. All these properties indicate that AtT20 cell tubular endosomes are an early endocytic compartment distinct from late endosomes. Tubular endosomes like those in AtT20 cells have been seen in cells of the following lines: PC12, HeLa, Hep2, Vero, MDCK I and II, CCL64, RK13, and NRK; they are particularly abundant in the first three lines. In contrast, tubular endosomes are sparse in 3T3 and BHK21 cells. The tubular endosomes we have observed appear to be identical to the endosomal reticulum observed in the living Hep2 cells by Hopkins, C. R., A. Gibson, H. Shipman, and K. Miller. 1990.

Behavior of a transitional tubulovesicular compartment at the cis side of the Golgi apparatus in in vivo fusion studies of mammalian cells

We have investigated the behavior in in vivo cell fusion experiments of a transitional compartment lying between the endoplasmic reticulum and Golgi apparatus to determine if the compartment, as recognized by the antibody G1/93, might congregate in a similar manner to Golgi apparatus [W. C. Ho et al. (1990) Eur. J. Cell Biol. 52, 315-327]. The distributions of the transitional tubulovesicular compartment, endoplasmic reticulum, and Golgi apparatus in HeLa cells were assessed by immunofluorescent staining using mouse monoclonal antibody G1/93, mouse monoclonal antibody HP 24, and rabbit anti-galactosyltransferase, respectively. In agreement with previous results [W. C. Ho et al. (1990) Eur. J. Cell Biol. 52, 315-327], the Golgi apparatus was observed to congregate gradually over a 3- to 6-h period, forming a large, extended, central Golgi complex in uv-inactivated Sindbis virus-fused HeLa cells. Concomitant with this was a marked congregation of the transitional tubulovesicular compartment. Congregation of the tubulovesicular compartment was not affected by cycloheximide. The endoplasmic reticulum retained its web-like distribution throughout the syncytoplasm and rimmed the nuclear periphery. Treatment of HeLa cells with nocodazole prior to fusion followed by incubation of the syncytia in drug-containing media blocked congregation of the G1/93-positive compartment. With this long-term nocodazole treatment, Golgi apparatus was dispersed into scattered Golgi elements and the G1/93 distribution was endoplasmic reticulum-like. These results suggest that the transitional tubulovesicular compartment recognized by G1/93 is normally structured on microtubules and microtubule organizing centers and may be considered to be a subcompartment of a greater, perinuclear, Golgi complex.

Golgi apparatus of epithelial principal cells of the epididymal initial segment of the rat: structure, relationship with endoplasmic reticulum, and role in the formation of secretory vesicles

The initial segment of the epididymis of rats, fixed with glutaraldehyde, was postfixed with reduced osmium, a technique that clearly delineates the membranes of cisternae of the endoplasmic reticulum (ER) and the various elements of the Golgi apparatus, or with tannic acid to enhance the coats of vesicles and ribosomes on ER cisternae. The material was also treated to demonstrate various phosphatase activities (NADPase, TPPase, CMPase, G-6-Pase) or impregnated with osmium tetroxide. In osmium-impregnated material, the Golgi apparatus of the epithelial principal cells of the initial segment appeared in the light microscope as a branching, anastomosing ribbon forming a large network in the supranuclear region. In the electron microscope, ER were of two types: the heavily granulated, flattened, rough ER seen in the infranuclear and juxtanuclear regions and the distended, tubular, sparsely granulated ER, showing only few ribosomes, seen interlaced with the Golgi ribbon in the supranuclear region and at the apical pole of the cell. Of particular interest in this cell was the fact that the sparsely granulated ER approximated the Golgi stack on both its cis- and trans-faces. On the cis-face of the Golgi stack, the sparsely granulated ER cisternae showed the usual finger- or bud-like protrusions directed toward the cis element of the Golgi stack and around which numerous small 80 nm vesicles or membranous tubules were clustered. The Golgi stack consisted of the following elements in a cis-trans axis: the cis osmiophilic element, a first saccule slightly dilated, saccules two to four (S2-S4), which were NADPase-positive, and saccules five to seven and the eight Golgi element, which were TPPase-positive. On the trans-aspect of the Golgi stacks, several (up to four) CMPase-positive trans-Golgi networks were observed often in close apposition to the sparsely granulated ER cisternae. One of the trans-Golgi networks showed a "peeling-off" configuration, i.e. part of it was closely apposed to the overlying Golgi element of the stack, whereas the remaining part was separated from the stack by a space occupied by a cisterna of sparsely granulated ER. The other trans-Golgi networks were completely separated from the stack and were often seen sandwiched between sparsely granulated ER cisternae. Thus, ER cisternae showed extensive areas of close apposition but no continuity with the trans-Golgi networks. Although the saccules of the Golgi stacks showed NADPase and/or TPPase activity, the trans-Golgi networks displayed CMPase activity, thus facilitating their identification from the closely associated unreactive sparsely granulated ER cisternae.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Tubulovesicular processes emerge from trans-Golgi cisternae, extend along microtubules, and interlink adjacent trans-golgi elements into a reticulum

Morphological dynamics and membrane transport within the living Golgi apparatus of astrocytes labeled with NBD-ceramide were imaged using both electronically enhanced fluorescence video and laser confocal microscopy. In time-lapse recordings, continuous tubulovesicular processes are observed to emerge from trans-Golgi elements and extend along microtubules at average rates of 0.4 microns/s. In addition, discrete fluorescent particles are observed to emerge from the trans-Golgi and subsequently migrate along microtubules at comparable velocities. Frequently, tubulovesicular processes form stable connections that interlink adjacent trans-Golgi elements into an extensive reticulum. Laser photobleaching-recovery experiments reveal that tubulovesicular processes can provide direct pathways for the diffusion of membrane lipids between joined trans-Golgi elements. These results suggest that microtubule-based transport and membrane fusion can operate to interconnect certain cisternal membranes of adjacent Golgi elements within the cell.

Ultrastructural distribution of NADPase within the Golgi apparatus and lysosomes of mammalian cells

Cytochemical studies with over 40 different mammalian cell types have indicated that NADPase activity is associated with the Golgi apparatus and/or lysosomes of all cells. In the majority of cases, NADPase is restricted to saccular elements comprising the medial region of the Golgi stack and an occasional lysosome. There is often weak NADPase activity in other Golgi compartments such as the trans Golgi saccules and/or elements of the trans Golgi network. In some cells, however, strong NADPase activity is found within these latter compartments, either exclusively in trans Golgi saccules or elements of the trans Golgi network, or in combination with medial Golgi saccules and each other including (1) medial Golgi saccules + trans Golgi saccules, (2) medial Golgi saccules + trans Golgi saccules + trans Golgi network, or (3) trans Golgi saccules + trans Golgi network. In some rare cases, no NADPase activity is detectable in either Golgi saccules or elements of the trans Golgi network, but it is observed in an occasional lysosome or throughout the lysosomal system of these cells. It is unclear at present if these variations in the distribution of NADPase across the Golgi apparatus, and between the Golgi apparatus and lysosomal system, are due to differences in targeting mechanisms or to the existence of "bottlenecks" in the natural flow of NADPase along the biosynthetic pathway toward lysosomes. While no clear pattern in the association of strong NADPase activity with lysosomes was apparent relative to the ultrastructural distribution of NADPase activity in Golgi saccules or elements of the trans Golgi network, the results of this investigation suggested that cells having NADPase localized predominantly toward the trans aspect of the Golgi apparatus (in trans Golgi saccules or elements of the trans Golgi network or both) have few NADPase-positive lysosomes. The only exception is hepatocytes which were classified as predominantly trans but had noticeable NADPase activity within medial Golgi saccules and elements of the trans Golgi network as well, and highly reactive lysosomes. Other cells showing highly reactive lysosomes including (1) Kupffer cells of liver and those forming the proximal convoluted tubules of the kidney, both of which also had strong NADPase activity within medial and trans Golgi saccules and elements of the trans Golgi network, (2) Leydig cells of the testis and interstitial cells of the ovary, which also showed strong NADPase activity within medial Golgi saccules, and (3) macrophages from lung, spleen and testis, and Sertoli cells from the testis all of which showed no Golgi associated NADPase activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Granule formation and polarity of the Golgi apparatus in neutrophil granulocytes of the rat

The formation of granules in neutrophil (heterophil) progenitor cells was examined with the electron microscope in sections of rat bone marrow fixed in 2% glutaraldehyde and postfixed with reduced osmium (Karnovsky: Proceedings of the 11th Meeting, American Society of Cell Biologists, Abstr. 284, p. 146, 1971). The cells were also osmicated in 2% osmium tetroxide for 36 hours at 37 degrees C to outline the osmiophilic element usually observed on the cis-face of the stacks of saccules of the Golgi apparatus of various cell types. In myeloblasts, which do not produce granules, the cis-osmiophilic element (CE) was found on the concave face of the C-shaped Golgi stacks. In promyelocytes the CE was present on the convex aspect of the C-shaped stacks, while the primary (azurophilic) granules formed in relation to elements on the concave aspects of the stacks. In myelocytes, the situation was reversed: the CE was found on the concave face of the Golgi stacks, while the secondary (specific) granules were seen forming in relation to elements on the convex aspect of the stacks. Finally, in metamyelocytes and mature neutrophils in which no granule formation took place, the appearance on Golgi stacks varied: they were either flat or C-shaped. The CE was indiscriminately found on one face or the other of the flat Golgi stacks of metamyetocytes and on the convex or concave faces of the C-shaped Golgi stacks of mature neutrophils. Using the cis-osmiophilic-element as a marker of the cis-face of the stacked Golgi elements, it thus appeared that despite marked changes in the configuration and orientation of the stacks of the cis-trans polarity of the stacked elements was maintained throughout granulopoiesis. In addition the primary and secondary granules that appeared sequentially in promyelocytes and myelocytes were both seen to form in relation to trans-elements of the Golgi apparatus.

The dynamic nature of the Golgi complex

The intracellular transport of newly synthesized G protein of vesicular stomatitis virus is blocked at 20 degrees C and this spanning membrane glycoprotein accumulates in the last Golgi compartment, the trans Golgi-network (TGN). Previous morphological evidence suggested that the TGN enlarged significantly under this condition. In the present study we have used stereological procedures to estimate the volume and surface area of the Golgi stack and the TGN of baby hamster kidney cells under different conditions. The results indicate that the increase in the size of the TGN at 20 degrees C is accompanied by a significant decrease in the surface area and volume of the preceding Golgi compartments. A similar effect is also seen in uninfected cells at 20 degrees C, as well as during normal (37 degrees C) infection with Semliki Forest virus. In the latter case, however, the decrease in the size of the Golgi stack and the increase in that of the TGN is not accompanied by inhibition of transport from the Golgi complex to the cell surface. The results indicate that the Golgi stack and the TGN are dynamic and interrelated structures that are capable of rapid alteration in total surface area in response to changes in the rates of membrane transport.

Formation of secretion granules in the Golgi apparatus of plasma cells in the rat

The three-dimensional structure of the components of the Golgi apparatus was analyzed in plasma cells of rat duodenum. The spheroidal juxtanuclear Golgi apparatus was formed by a continuous ribbonlike structure composed of the following stacked elements. On the cis-face of the Golgi stack, there was a tubular membranous network referred to as the cis-element and/or a slightly dilated saccule perforated with small pores. The two or three subjacent saccules, which showed few pores, were slightly dilated and contained a fluffy granulofilamentous material. They were also perforated in register by cavities or wells containing 80-nm vesicles. The next one or two underlying elements were fenestrated saccules showing flattened portions as well as distended portions containing a homogeneous material denser than that seen in the overlying saccules. The last two or three elements of the stack showed a partially separated or "peeling off" configuration. These last elements consisted of prosecretory granules attached to flattened, empty-looking saccules showing buds at their surface; detached, more-or-less fenestrated, flattened saccules; and shrivelled residual trans-tubular networks. In the trans-region of the stack, in addition to numerous small vesicles, short membranous tubules, detached prosecretory granules, and denser fully formed secretion granules were also seen. These images were interpreted to indicate that secretory material present in the trans-saccules flows toward the dilated portions which become prosecretory granules. The trans-most elements seemingly peel off the stack to yield prosecretory granules and fragmenting trans-tubular networks.

Formation of secretion granules in the Golgi apparatus of pancreatic acinar cells of the rat

The three-dimensional structure of the Golgi apparatus and its components has been analyzed in sections of pancreatic acinar cells by using stereopairs of electron microscope photographs. Pancreatic tissue fixed in glutaraldehyde was postfixed in reduced osmium, and the sections were stained with lead citrate. Tissues were also treated to demonstrate phosphatase activity (i.e., nicotinamide adenine dinucleotide phosphatase, NADPase; thiamine pyrophosphatase, TPPase; cytidine monophosphatase, CMPase). The following stacked components were observed along the branching, anastomotic, continuous, ribbonlike Golgi apparatus. 1) On the cis-face of the Golgi stack there was a tubular membranous network known to be osmiophilic and referred to as the cis-osmiophilic tubular network or cis-element. 2) A first, poorly fenestrated saccule, unreactive for the phosphatases tested, was slightly distended in places and contained a fluffy granulofilamentous material. 3) The subjacent three or four saccules, reactive for NADPase and/or TPPase, showed dilated portions containing a granulofilamentous secretory material similar to that filling the rest of the saccule. They also showed nondilated portions perforated with large fenestrations, some of which were in register and formed wells containing 80-nm vesicles. The dilated portions of these saccules were present at random along the length of the saccules and were not located exclusively at their edges. 4) The remaining one or two elements of the stack, CMPase positive, showed dilated spheroidal portions or prosecretory granules containing a homogeneous secretory material and flattened fenestrated regions free of secretory material and having the appearance of networks of narrow membranous tubules. 5) Lastly on the trans-aspect of the stack there were detached prosecretory granules reactive for CMPase and surrounded by a corona of small vesicles, and smooth-surfaced spherical CMPase-negative granules having a denser content that were identified as fully formed secretion granules; there were also occasional free trans-tubular networks strongly reactive for CMPase that appeared to undergo fragmentation and numerous small vesicles free from acid-phosphatase activity. These various images were interpreted as indicating that prosecretory granules formed in relation to two or three fenestrated saccules on the trans-side of the stack. Such granules, following their detachment from the trans-face of the stack, their separation from trans-tubular networks, and condensation of their content, yielded mature secretion granules.

Tridimensional architecture of the Golgi apparatus and its components in mucous cells of Brunner's glands of the mouse

The three-dimensional structure of the Golgi apparatus and its components has been analyzed in thin and thick sections of mucous cells of mouse Brunner's glands by using low- and high-voltage electron microscopes and a stereoscopic approach. In thick sections of glands impregnated with osmium or treated to detect nicotinamide adenine dinucleotide phosphatase (NADPase) or thiamine pyrophosphatase (TPPase) activity, the Golgi apparatus appeared, at low magnification, as a continuous network located in the supranuclear region. At higher magnifications and in thin sections of tissue postfixed with reduced osmium and stained with lead citrate or treated to demonstrate phosphatase activity, the following components were observed: on the cis-face of the Golgi stacks, an osmiophilic tubular network referred to as the cis-element; a cis-saccular-compartment composed of a distended porous saccule slightly reactive for NADPase and three or four underlying NADPase-positive, flattened, poorly fenestrated saccules; a trans-saccular-compartment consisting of four to six TPPase-positive saccules or sacculo-tubular elements, prosecretory granules, and "peeling off" trans-tubular networks. The saccules of the cis-compartment were often perforated by large pores in register. The cavities thus formed in the stacks were called wells and were pan-shaped with a mouth directed toward the cis-face of the stacks and a bottom closed by TPPase-positive saccules. The wells always contained 80-nm vesicles. The saccules of the trans-compartment were involved in the formation of secretory granules according to the following proposed sequence of transformation. The secretion product appeared initially as a granular material evenly distributed throughout a slightly distended, poorly fenestrated saccule. These saccules appeared to transform into fenestrated elements with irregular pores and with parts of them taking on the appearance of a tubular network; they were thus referred to as sacculotubular elements. The secretory material initially distributed throughout these elements accumulated in nodular dilatations randomly distributed along the tubular portions of the elements. The dilatations, considered as prosecretory granules, increased in size as they drained the secretory material from the rest of the sacculotubular elements. Such prosecretory granules, large and irregular in shape, "peeled off" from the stacks of saccules with residual saccular or tubular structures still attached to them, some of the latter forming trans-tubular networks. The prosecretory granules detached from such membranous residues, condensed, and finally transformed into spherical secretion granules.

Ultrastructural localization of concanavalin A-binding sites in the Golgi apparatus of various types of neurons in rat dorsal root ganglia: functional implications

The localization of concanavalin A (con A) binding sites has been determined at the electron-microscopic level in the six types of neurons (A1, A2, A3, B1, B2, C) of rat dorsal root ganglia. In all ganglion cells, con A stained the plasma membrane, the nuclear envelope, the cisternae of the rough endoplasmic reticulum, and the matrix of some multivesicular bodies. In contrast, the con A reactivity of the Golgi apparatus varied according to cell type. In type B1 and B2 cells and possibly in type A3 cells, the lectin was exclusively located in three or four saccules on the cis side of the Golgi stacks, whereas the TPPase-positive saccules and the trans sacculotubular elements were unstained with con A. In type A1, A2, and C neurons, all Golgi saccules as well as the trans sacculotubular elements were stained with the lectin. These results suggest that different types of glycoproteins were produced in these two groups of neurons. In the type A1, A2, and C cells, the persistence of the lectin reactivity in the TTPase-positive saccules or sacculotubular elements on the trans side of the Golgi stacks suggests the presence of glycoproteins with oligosaccharide side chains rich in alpha-D-mannosyl residues in terminal positions. In contrast, the disappearance of the con A reactivity in equivalent elements of the Golgi stacks in type B1, B2, and A3 cells suggests the addition at this level of other sugar residues characteristic of complex oligosaccharide side chains. The majority of the vesicular elements associated with the Golgi apparatus, as well as lysosomes, were unstained with con A.