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At least 289 records · Page 16Linked to original sources
PubMed1995

BCMAp: an integral membrane protein in the Golgi apparatus of human mature B lymphocytes.

BCMA is a human gene expressed preferentially in mature B lymphocytes as a 1.2 kb mRNA, which encodes a 184 amino acid peptide (BCMAp). The study of BCMA mRNA expression, using human malignant B cell lines characteristic of different stages of B lymphocyte differentiation, demonstrated that the BCMA mRNA is absent in the pro-B lymphocyte stage. It is expressed faintly at the pre-B cell stage and its expression increases with B lymphocyte maturation. Polyclonal antibodies were used to show, by cellular fractionation and immunoprecipitation, that BCMAp is a non-glycosylated integral membrane protein. Furthermore, BCMAp inserts, in vitro, into canine microsomes, as a type I integral membrane protein. Cell surface labeling showed that BCMAp is not expressed in the plasma membrane of mature B lymphocytes. Immunofluorescence studies revealed that BCMAp lies in a cap-like structure near the nucleus, that was identified as the Golgi apparatus by co-localization of BCMAp with CTR433, a marker of the medial cisternae of the Golgi apparatus. Confocal scanning laser microscopy of U266 plasma cells labeled with markers of various Golgi apparatus subcompartments strongly suggests that BCMAp is located in the cis part of the Golgi apparatus. Thus, BCMAp is the first Golgi resident protein with a tissue specificity and whose expression is linked to the stage of differentiation of B lymphocytes. The location of BCMAp in the Golgi apparatus and its high expression in plasmocytes (secreting large amounts of Ig) suggest that BCMAp is implicated in the intracellular traffic of Ig.

B-Cell Maturation Antigen↗
PubMed2004

Use of taxol and collagenase for better three-dimensional visualization of microtubules in the enterocyte and Brunner's gland cell, with special reference to their relation to the Golgi apparatus.

Cytoskeletal microtubules were visualized in the mouse duodenal mucosa by an improved immunofluorescence method using a microtubule-stabilizing reagent, Taxol, and collagenase as an enzymatic epitope retriever. The improvement in immunostaining was shown morphologically and statistically by comparing fluorescence intensities of specimens prepared with or without Taxol and collagenase treatment. In free cells in the epithelium and in the lamina propria, microtubules radiated from the gamma-tubulin-immunostained organizing center. Enterocytes and Brunner's gland cells double-stained with an anti-alpha-tubulin antibody and a lectin (Helix pomatia agglutinin, soybean agglutinin or Ulex europaeus agglutinin-I) showed that microtubules ran along the cell axis and were abundant between the Golgi apparatus and the apical surface. The microtubules appeared to provide a structural support to hold the Golgi apparatus in position and to act as railways for secretory granules, which are transported towards the apical surface. In addition, gamma-tubulin-like immunoreactivity was associated with the Golgi apparatus in the enterocytes. These results show that the method using Taxol and collagenase is effective for visualizing microtubules in epithelial cells, and that microtubules may play important roles in both positioning of the Golgi apparatus and transport of secretory granules. Our results also support the idea that the Golgi apparatus may act as an organizing center for microtubules.

Animals↗
PubMed1987

Polypeptides of the Golgi apparatus of neurons from rat brain.

An antiserum was raised against fractions of the Golgi apparatus of neurons from rat brain. Immunoblots of these fractions with the antiserum showed two principal bands of 185 and 150 kilodaltons (kd) in apparent molecular mass. The antiserum reacted with five or six bands of 200, 150, 130, 100-110, 64, and 40 kd in apparent molecular mass in immunoblots of several crude brain membrane fractions. Affinity-purified antibodies from the different gel bands transferred to nitrocellulose paper were used in immunoblot and immunocytochemical studies. Antibodies eluted from the 200-, 150-, 100-110-, and 64-kd bands reacted not only with the corresponding band but also with the other three bands. Antibodies eluted from the 40-kd band stained only the corresponding band. On light and/or electron microscopic immunocytochemistry, the antiserum stained the Golgi apparatus of rat neurons, glia, liver, and kidney tubule cells. Weaker, segmented, and less consistent staining was observed in nuclear envelopes, rough endoplasmic reticulum, and plasma membranes of neurons. Antibodies eluted from the bands at 200, 150, 100-110, and 64 kd stained intermediate cisterns of the Golgi apparatus of neurons. These findings suggest that a group of related polypeptides of brain membranes is preferentially expressed or enriched in the Golgi apparatus of neurons. Polypeptides with apparent molecular masses of 185 and 150 kd probably represent moieties endogenous to membranes of the neuronal Golgi apparatus.

Animals↗
PubMed1992

Chronic ethanol consumption induces accumulation of proteins in the liver Golgi apparatus and decreases galactosyltransferase activity.

The effect of chronic ethanol consumption on labeled glycoprotein secretion and galactosyltransferase activity has been analyzed in cis- and trans-Golgi apparatus fractions isolated from rat liver. Rats were injected intraperitoneally with 3H-leucine, after different chase periods (30, 60, 180 min), and the radioactivity of the different subcellular fractions as well as of the isolated Golgi apparatus was measured. Chronic alcohol treatment induces an increase in liver weight as well as an enhancement of total liver protein. Ethanol treatment produces a significant accumulation of labeled proteins in isolated Golgi apparatus fractions after a 60- and 180-min chase. An accumulation of labeled proteins in the cytosolic fraction was observed only after 180 min. The alcohol treatment also induces a significant decrease in the activity of galactosyltransferase in both liver homogenate and Golgi apparatus fractions. These results suggest that an impairment of Golgi apparatus functions, including glycosylation and glycoprotein trafficking, could be one of the mechanisms involved in the accumulation of hepatic protein and thus in the pathogenesis of alcohol-induced injury in the liver of chronic ethanol-consuming animals.

Alcoholism↗
PubMed1995

Redistribution of microtubules and Golgi apparatus in herpes simplex virus-infected cells and their role in viral exocytosis.

Earlier studies have shown that the Golgi apparatus was fragmented and dispersed in herpes simplex virus 1-infected Vero and HEp-2 cells but not in human 143TK- cells, that the fragmentation and dispersal required viral functions expressed concurrently with or after the onset of DNA synthesis (G. Campadelli-Fiume, R. Brandimarti, C. Di Lazzaro, P. L. Ward, B. Roizman, and M. R. Torrisi, Proc. Natl. Acad. Sci. USA 90:2798-2802, 1993), and that in 143TK- cells, but not Vero or HEp-2 cells, infected with viral mutants lacking the UL20 gene virions were glycosylated and transported to extracellular space (J. D. Baines, P. L. Ward, G. Campadelli-Fiume, and B. Roizman, J. Virol. 65:6414-6424, 1991; E. Avitabile, P. L. Ward, C. Di Lazzaro, M. R. Torrisi, B. Roizman, and G. Campadelli-Fiume, J. Virol. 68:7397-7405, 1994). Experiments designed to elucidate the role of the microtubules and of intact or fragmented Golgi apparatus in the exocytosis of virions showed the following. (i) In all cell lines tested (Vero, 143TK-, BHK, and Hep-2) microtubules underwent fragmentation particularly evident at the cell periphery and then reorganized into bundles which circumvent the nucleus. This event was not affected by inhibitors of viral DNA synthesis. We conclude that redistribution of microtubules may be required but is not sufficient for the fragmentation and dispersal of the Golgi apparatus. (ii) In all infected cell lines tested, nocodazole caused fragmentation and dispersal of the Golgi and a far more extensive depolymerization of the microtubules than was seen in untreated, infected Vero or HEp-2 cells. Taxol precluded the depolymerization of the microtubules and fragmentation of the Golgi in both infected cell lines. Neither nocodazole nor taxol affected the exocytosis of infectious virus from Vero, HEp-2, or 143TK- cells infected with wild-type virus. We conclude that the effects of nocodazole or of taxol are dominant over the effects of viral infection in the cell lines tested and that viral exocytosis is independent of the organization of microtubules or of the integrity of the Golgi apparatus. Lastly, the data suggest that herpes simplex viruses have evolved an exocytic pathway for which the UL20 protein is a component required in some cells but not others and in which this protein does not merely compensate for the fragmentation and dispersal of the Golgi apparatus.

Animals↗
PubMed1995

MG-160, a membrane sialoglycoprotein of the medial cisternae of the rat Golgi apparatus, binds basic fibroblast growth factor and exhibits a high level of sequence identity to a chicken fibroblast growth factor receptor.

We report the primary structure of MG-160, a 160 kDa membrane sialoglycoprotein residing in the medial cisternae of the Golgi apparatus of rat neurons, pheochromocytoma (PC-12), and several other cells. The cDNA encodes a polypeptide of 1,171 amino acids with an M(r) of 133,403. An intralumenal cleavable signal peptide is followed by a Pro-Gln-rich segment and 16 contiguous, approx. 60-residue-long, regularly spaced cysteine-rich segments showing sequence identities ranging from 15 to 35%. The lumenal domain is followed by a single membrane spanning domain and a short carboxy-terminal cytoplasmic tail. The protein contains 5 potential NXT glycosylation sites. The sequence of MG-160 shows no homologies with enzymes and other membrane proteins of the Golgi apparatus. MG-160 displays a so far unique feature for a membrane protein of the Golgi apparatus: namely, an upstream, open reading frame (uORF), encoding 58 amino acids, located in front of the major open reading frame (ORF). Most vertebrate mRNAs containing uORF or AUG codons in front of the major ORF encode growth factors and cell surface receptors (Geballe and Morris 1994). In that regard a 90% identity between the primary structure of MG-160 and a receptor for acidic and basic fibroblast growth factors (CFR), isolated from chicken embryos (Burrus et. al., 1992), may be relevant. Immunoreactivity for MG-160 has been detected in the Golgi apparatus of neural and other cells of 2-day-old chicken embryos and adult chicken; furthermore, recombinant human basic fibroblast growth factor (bFGF) binds MG-160 purified from rat brain. MG-160 shows no sequence similarity with members of the family of fibroblast growth factor receptors (FGFR) involved in signal transduction. These findings are consistent with the hypothesis that MG-160 is involved in the traffic and processing of endogenous or autocrine FGFs. This is the first example of an intrinsic membrane protein of the Golgi apparatus which binds a growth factor and may be involved in its regulation.

Amino Acid Sequence↗
PubMed1999

Dynamic association of cytoplasmic dynein heavy chain 1a with the Golgi apparatus and intermediate compartment.

Microtubule motors, such as the minus end-directed motor, cytoplasmic dynein, play an important role in maintaining the integrity, intracellular location, and function of the Golgi apparatus, as well as in the translocation of membrane between the endoplasmic reticulum and Golgi apparatus. We have immunolocalised conventional cytoplasmic dynein heavy chain to the Golgi apparatus in cultured vertebrate cells. In addition, we present evidence that cytoplasmic dynein heavy chain cycles constitutively between the endoplasmic reticulum and Golgi apparatus: it colocalises partially with the intermediate compartment, it is found on nocodazole-induced peripheral Golgi elements and, most strikingly, on Brefeldin A-induced tubules that are moving towards microtubule plus ends. The direction of movement of membrane between the endoplasmic reticulum and Golgi apparatus is therefore unlikely to be regulated by controlling motor-membrane interactions: rather, the motors probably remain bound throughout the whole cycle, with their activity being modulated instead. We also report that the overexpression of p50/dynamitin results in the loss of cytoplasmic dynein heavy chain from the membrane of peripheral Golgi elements. These results explain how dynamitin overexpression causes the inhibition of endoplasmic reticulum-to-Golgi transport complex movement towards the centrosomal region, and support the general model that an intact dynactin complex is required for cytoplasmic dynein binding to all cargoes.

Amino Acid Sequence↗
PubMed1976

Similarities of the Golgi apparatus membrane and the plasma membrane in rat liver cells.

A Golgi apparatus-rich fraction and a plasma membrane-rich fraction were isolated from a common homogenate of rat liver. Their respective buovant densities, appearances in the electron microscope and 5'-nucleotidase and UDP-galactose ovalbumin galactosyltransferase activities were in accord with published data on separately isolated Golgi apparatus-rich and plasma membrane-rich fractions. Contamination by endoplasmic reticulum and mitochondria was low. Gel electrophoresis of the membrane proteins of the Golgi apparatus-rich and plasma membrane-rich fractions (separately and mixed) showed a close similarity. After Neville's demonstration that electrophoretic patterns of membrane protein subunits from different subcellular fractions are easily distinguishable, the present work demonstrates an unusually close relationship between the Golgi apparatus membrane and the cell membrane. It is possible that membrane similarity may be mediated by the transfer of membrane-bound vesicles from the Golgi apparatus to the cell membrane.

Animals↗
PubMed1978

The ATP-dependent concentration of calcium by a Golgi apparatus-rich fraction isolated from rat liver.

Fractions rich in Golgi apparatus were isolated from female rat liver and incubated with different concentrations of MgATP and calcium. Calcium was sequestered by the fraction in the presence but not in the absence of ATP. The kinetics of the uptake process showed an exponential type accumulation to a maximum value which could be explained by a 'pumpleak' mechanism where Vmax was estimated at 6.7 nmol calcium/mg protein/min. Apparent Km for ATP was 1 mM and for calcium was 85 micron. The uptake is not inhibited in 5 mM azide, nor is it enhanced in 5 mM oxalate, suggesting that the sequestration is not caused by contamination from mitochondria or microsomes. Parallel experiments on a fraction rich in plasma membrane show at least a 10-fold reduction of activity over the Golgi apparatus-rich fraction, which is interpreted as evidence that plasma membrane contamination in the Golgi apparatus-rich fraction is not primarily responsible for the calcium sequestration activity. Morphometric analysis showed that about 85% of the recognizable membrane profiles in the fraction was associated with elements of the Golgi apparatus. Further evidence is given which suggests that at least 90% of the fraction was uniform in its ability to sequester calcium. In preliminary experiments it was not found possible to separate galactosyltransferase activity (a secific enzyme associated with the Golgi apparatus) from the calcium-sequestration mechanism. The stoichiometry of the hydrolysis of ATP associated with the uptake of calcium is the same as that shown by other isolated membrane systems.

Adenosine Triphosphate↗
PubMedDate not supplied

Development and congenital abnormalities of the nasolacrimal apparatus.

The development of the nasolacrimal apparatus was reassessed based on the examination of serial sections done in 27 (54 orbits) embryos and fetuses ranging in size from 13.6 mm to term. In addition two adult specimens were examined. The entire nasolacrimal apparatus viz. canaliculi, lacrimal sac, and nasolacrimal duct develop contemporaneously. Canalization thereafter occurs throughout its length at the same time. The epithelium which lines the nasolacrimal apparatus abuts against the conjunctival epithelium superiorly in relationship to the puncta and the nasal mucosa at the opening of the nasolacrimal duct. These gossamer-like membranes perforate at term or soon thereafter. With the development of the face, the maxillary process grows medially to abut against, and then to override, the paraxial mesoderm of the nasolacrimal process. The nasooptic fissure is thus formed between these two mesodermal complexes. The surface ectoderm within the fissure thickens in a cord-like fashion and this is the analaga of the nasolacrimal apparatus. There is divergence of opinion as to the subsequent development of tear drainage system. A cord of epithelial cells forms from the nasal cavity and grows cephalad to become continuous with the main cord of buried surface ectoderm (Figure 1). It has been contended by Duke-Elder that the main epithelial cord then sends extensions laterally to form the superior and the inferior canaliculi. The inferior canaliculus extends more laterally than the superior canaliculus. At 3 months' development, canalization of the nasolacrimal apparatus is purported to occur in a segmental manner. These cavities then coalesce in a haphazard manner, finally forming a continuous tube. It is also suggested that the main core of buried epithelium canalizes from cephal caudalwards and that the epithelium arising from the nasal cavity canalizes in a reverse direction. The lacrimal sac then expands: the canaliculi canalize and the final section of the nasolacrimal duct to become patent is the opening into the inferior meatus of the nose below the inferior meatus of the nose below the inferior turbinate.U

Humans↗
PubMed1991

A part of glucosylceramide formed from exogenous lactosylceramide is not degraded to ceramide but re-cycled and glycosylated in the Golgi apparatus.

The subcellular fate of glucosylceramide (GlcCer) formed from exogenous lactosylceramide (LacCer) in rat liver is investigated. LacCer radiolabeled on different positions of the molecule was intravenously administered to rats as a liposomal dispersion. A Golgi apparatus fraction 140-fold enriched in specific markers and constituted by intact cisternal stacks, as well as the lysosomal and plasma membrane fractions concurrently prepared from the same homogenate, were then studied in order to determine the time course of radioactive glycosphingolipids. LacCer quickly decreased with time in the plasma membrane, whereas in the lysosomes it increased up to 4 h and decreased thereafter. In both fractions results were regardless of the labeling position. In the Golgi apparatus, LacCer increased up to 12 h and then decreased. In this fraction, the radioactivity values of [Glc-3H]LacCer were over twice those of [Gal-3H]LacCer. GlcCer was found only after [Glc-3H]LacCer administration. In the lysosomes, its time course provided a peak similar in shape but delayed in timing with respect to that of LacCer. Conversely, in the Golgi apparatus GlcCer was earlier formed, but earlier consumed, than LacCer. Gangliosides increased in the Golgi apparatus until 4 h and then decreased after 12 h, whereas in the plasma membrane they were progressively accumulated. In both fractions the amount of [Glc-3H]gangliosides was over twice that of [Gal-3H]gangliosides was over twice that of [Gal-3H]gangliosides. Since we demonstrated that the sugars released in the course of LacCer degradation (LacCer----galactose + GlcCer----glucose + ceramide) are not incorporated into glycoconjugates, we conclude that a part of GlcCer formed during the lysosomal degradation of LacCer actually reaches the Golgi apparatus where it undergoes successive glycosylation.

Animals↗
PubMed1991

Accumulation of glycoprotein in the Golgi apparatus of hepatocytes in alcoholic liver injuries.

To clarify the role of the hepatocytic Golgi apparatus in the accumulation of proteins in the hepatocytes of alcoholic liver disease, changes in the Golgi apparatus in human and experimental alcoholic liver injuries were analyzed. Immunoelectron microscopically, transferrin, one of the secretory glycoproteins from the liver, was retained in the smooth endoplasmic reticulum and Golgi apparatus of the hepatocytes in both human and rat alcoholic liver injuries. Biochemically, transferrin content in the Golgi fraction was clearly high in the rats with alcoholic liver injury. Desialo-glycoproteins were found in the serum of rats with alcoholic liver injuries. These results suggested that the glycosylation and secretion of hepatic glycoproteins in the Golgi apparatus were impaired in alcoholic liver injury. These abnormalities in the Golgi apparatus function may be important for the development of alcoholic liver injury.

Analysis of Variance↗
PubMed1990

The occurrence of the Golgi apparatus in mouse oocytes. Demonstration of thiamine pyrophosphatase activity.

Location of thiamine pyrophosphatase activity as a marker of the Golgi apparatus was studied ultracytochemically in mouse oocytes with germinal vesicle (OGV), oocytes at metaphase I (OMI) and oocytes at metaphase II (OMII), and further in cells of the respective cumulus oophorus serving as comparative objects. TPPase activity in cumulus oophorus cells and in OGV was found exclusively in the Golgi apparatus. In OMI the reaction product of TPPase activity was observed in isolated smooth vesicles, and in only one case in structures identifiable as the Golgi apparatus. In OMII the occurrence of TPPase activity was also recorded in isolated smooth vesicles in cortical cytoplasm and further, exceptionally, in smooth concentrically arranged vesicles or tubules. The TPPase activity was not present in vesicular complexes. The results have shown that after the resumption of meiosis the occurrence of the reaction product of TPPase activity drops abruptly due to the reduction of the Golgi apparatus. Changes affecting the Golgi apparatus after the resumption of meiosis are related to the loss of the nucleus after the germinal vesicle breakdown.

Animals↗
PubMed1988

Post-Golgi apparatus localization and regional expression of rat intestinal sialyltransferase detected by immunoelectron microscopy with polypeptide epitope-purified antibody.

During studies on the Golgi apparatus immunolocalization of beta-galactoside alpha 2,6-sialyltransferase in intestinal cells, immunostaining of a number of post-Golgi apparatus structures including mucus droplets and plasma membrane were observed. In order to determine if this labeling was in fact due to sialyltransferase and not carbohydrate-specific antibodies in the polyclonal antiserum preparation, fusion protein to sialyltransferase was used to epitope purify polypeptide-specific antibodies. The affinity purification was performed on a column containing a beta-galactosidase-sialyltransferase fusion protein expressed in Escherichia coli. Using such antibodies we present evidence that in intestinal cells sialyltransferase is not only present in the Golgi apparatus cisternal stack but also its transtubular network and various post-Golgi apparatus structures. In absorptive enterocytes, post-Golgi apparatus vesicles, the brush border and basolateral plasma membrane, multivesicular bodies, and lysosome-like structures were labeled. In goblet cells the limiting membrane and lumen of forming and mature mucus droplets as well as the plasma membrane exhibited label for sialyltransferase. The results provide evidence for "ecto-sialyltransferase" in the plasma membranes of these cells, and suggest that most of the sialyltransferase is released from the Golgi membranes and becomes secreted with the goblet cell mucus. In addition, the polypeptide epitope-purified antibody was also used to examine regional expression of sialyltransferase in the rat intestinal epithelium. Immunolabel was restricted to the large intestine and not found in duodenum, jejunum, and ileum. Direct measurement of the enzyme activity was found to correlate with the immunoelectron microscopic data. This observation suggests that there is regional specific expression of the beta-galactoside alpha 2,6-sialyltransferase.

Animals↗
PubMed1986

Involvement of cis and trans Golgi apparatus elements in the intracellular sorting and targeting of acid hydrolases to lysosomes.

To delineate the traffic route through the Golgi apparatus followed by newly synthesized lysosomal enzymes, we subfractionated the Golgi apparatus of rat liver by preparative free-flow electrophoresis into cisternae fractions of increasing content of trans face markers and decreasing contents of markers for the cis face. NADPase was used to mark median cisternae. Beta-Hexosaminidase, the high mannose oligosaccharide processing enzyme, alpha-mannosidase II, the two enzymes involved in the biosynthesis of the phosphomannosyl recognition marker, and the phosphomannosyl receptor itself decreased in specific activity or amount from cis to trans. Additionally, these activities were observed in a fraction consisting predominantly of cisternae, vesicles and tubules derived from trans-most Golgi apparatus elements. These results, along with preliminary pulse-labeling kinetic data for the phosphomannosyl receptor, suggest that lysosomal enzymes enter the Golgi apparatus at the cis face, are phosphorylated, and appear in trans face vesicles by a route whereby the phosphomannosyl receptor bypasses at least some median and/or trans Golgi apparatus cisternae.

Acid Phosphatase↗
PubMed1988

An anti-organelle antibody in pathology. The chromatolytic reaction studied with a monoclonal antibody against the Golgi apparatus.

To evaluate the use of an anti-organelle antibody in a pathologic reaction the chromatolytic reaction was chosen for study. Qualitative analysis was made of rat hypoglossal nuclei stained with a cresyl violet method for Nissl substance and a monoclonal antibody against rat Golgi apparatus (10A8) 0 and 3 days, and 1, 2, 3, 4, 5, and 6 weeks after section of the right hypoglossal nerve. Marked dispersion of Nissl substance was noted at 2 weeks and of Golgi apparatus at 4 weeks. Reaggregation of staining had occurred for both organelles by 6 weeks. A quantitative light microscopic analysis was carried out for both stains on randomly selected hypoglossal sections from 0, 2, 4, and 6 weeks. The analysis confirmed the qualitative observations and showed them to be highly significant. In addition, it revealed an increase in nuclear area from 0 to 2 weeks, an increase in cytoplasmic area at 4 weeks, decrease in the total area of Nissl substance from 0 to 2 and 4 to 6 weeks, decrease in the percent cytoplasmic areas occupied by Nissl from 0 to 2 weeks and decreases in both the total and percent cytoplasmic area occupied by Golgi apparatus maximal at 4 weeks. Both qualitative and quantitative analyses confirmed the use of this monoclonal antibody to study morphologic changes of the Golgi apparatus secondary to an experimental pathologic lesion. In addition, a previously unrecognized temporal dissociation between the changes of Nissl substance and Golgi apparatus was described.

Animals↗
PubMed1985

The neuronal endomembrane system. I. Direct links between rough endoplasmic reticulum and the cis element of the Golgi apparatus.

This is the first of three papers describing new components and structural relationships within the neuronal endomembrane system. This system includes: the nuclear envelope, rough endoplasmic reticulum, the Golgi apparatus, lysosomes, axoplasmic reticulum, and discrete cytoplasmic compartments such as vesicles, multivesicular bodies, and so on. Previous high voltage electron microscope studies of osmium-impregnated Golgi apparatus have shown that small varicose tubules often arise from the cis element. In bullfrog spinal ganglia, these tubules have been seen to extend into cytoplasmic domains occupied by rough endoplasmic reticulum (RER). This study was undertaken to determine whether varicose tubules form direct connections with RER and to measure cytoplasmic density of varicose tubules. Spinal ganglia from Rana catesbeiana were fixed by osmium impregnation and, in some cases, were then stained en bloc with lead aspartate. Sixty- to 3000-nm-thick sections of this tissue, as well as of ganglia prepared by conventional protocol, were studied using standard and high voltage electron microscopy. Quantitative analysis revealed that 9% of the varicose tubules connected with the Golgi cis element. To determine whether continuities existed between RER and any of these tubules, more than 50 tubules were fully reconstructed from images of serial sections. The "ends" of these reconstructed tubules were then studied by high magnification stereoscopy. This was facilitated by the en bloc lead staining which allowed visualization of unimpregnated RER elements along with the impregnated tubules. Small varicose tubules as well as larger smooth tubules were found to have formed confluent bridges between the cis element and RER. In addition, the varicose tubules were found to bridge widely separated elements of RER. Finally, numerous examples of varicose and smooth tubules were seen to extend from RER and from cis elements to eventually form blind endings. These findings raise the possibility that the tubules form highly dynamic transitory connections between RER and the Golgi apparatus as well as between separated elements of RER. Those between RER and Golgi apparatus are ideally positioned to play a major role in the transfer of protein or lipid components first assembled in RER to the Golgi apparatus for terminal synthetic modification.

Animals↗
PubMed1985

Kinetics of monensin-induced swelling of Golgi apparatus cisternae of H-2 hepatoma cells.

In H-2 hepatoma cells grown in culture, a pattern of response to the sodium-selective ionophore, monensin, was observed in which cisternal swelling commenced at one pole of the Golgi apparatus and was accompanied by the accumulation of swollen vacuoles in the cytoplasm in the absence of a decrease in the number of cisternae per stack. The results suggest that the swollen vacuoles are formed from Golgi apparatus cisternae that are replaced by formation of new cisternae. Depending on monensin concentration, between 2 and 4 such vacuoles accumulated per Golgi apparatus stack within 12.5 min after monensin addition. The rate of vacuole formation was greatest at 10(-6) M monensin and least at 10(-8) M monensin over the range 10(-5) to 10(-8) M monensin. The general pattern of early response to the ionophore is that formation of normal secretory vesicles is blocked, after which the Golgi apparatus continues to function for a time to release membrane as swollen cisternal units that accumulate in the cytoplasm at or near the trans Golgi apparatus face. These phenomena all precede the general swelling response normally observed in glutaraldehyde-fixed animal material and illustrate that the early dynamic responses to monensin are not confined to plant cells.

Animals↗