Golgi 58K-like protein in pollens and pollen tubes of Lilium davidii

In animal cells, Golgi apparatus is located near the microtubule organizing center (MTOC) and its position is determined partly by 58K protein. By sodium dodecyl-sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immuno-blotting methods, a 58K-like protein has been found in pollen grains and pollen tubes of Lilium davidii. Its molecular weight is very similar to that of the 58K protein of animal cells. By immunofluorescence labeling, under a confocal laser scanning microscope (CLSM), the animal 58K antibody revealed a punctate staining in pollen grains and pollen tubes, which is consistent with the distribution of Golgi apparatus in plant cells. In addition, immuno-gold labeling and transmission electron microscopy showed that the 58K-like protein bound mainly to the membrane of vesicles-like structure near Golgi apparatus. This is the first demonstration of the 58K-like protein in plant cells.     

Plant Golgi-associated vesicles contain a novel alpha-actinin-like protein

By using Western blotting, immunofluorescence and immunogold labeling, a novel alpha-actinin-like protein was found in pollen and pollen tubes of Lilium davidii, a model system for cytoskeleton and Golgi apparatus study of plant. As measured by Western blotting, the molecular mass of the a-actinin-like protein was about 80 kDa. Under confocal laser scanning microscopy after immunofluorescence labeling, the distribution of the alpha-actinin-like protein appeared punctated in the cytoplasm of the pollen and pollen tubes. When double labeled, the protein was co-localized with Golgi 58K protein. In addition, some fraction of the alpha-actinin-like protein was found to co-distribute with F-actin bundles in the pollen tubes. Additional studies with immuno-gold labeling and transmission electron microscopy revealed that the alpha-actinin-like protein bound mainly to the membranes of Golgi-associated vesicles. When the pollen tubes were treated with Brefeldin A (BFA), the a-actinin-like proteins were dispersed into the cytoplasm, and the growth of pollen tubes was inhibited. After BFA was removed, the protein was reversibly recovered on the Golgi apparatus. These results suggest that the novel alpha-actinin-like protein is a BFA-sensitive protein on the membranes of Golgi-associated vesicles, and may participate in Golgi-associated vesicles budding and/or sorting, together with actin microfilaments.     

Localization and secretory pathways of a 58K-like protein in multi-vesicular bodies in callus of Arabidopsis thaliana

Multi-vesicular bodies in endocytosis and protoplasts are special cellular structures that are consid-ered to be originated from invagination of plasma membranes. However, the genesis and function of multi-vesicular bodies, the relationship with Golgi bodies and cell walls, and their secretory pathways remain controversial and ambiguous. Using a monoclonal antibody against an animal 58K protein, we have detected, by Western blotting and confocal microscopy, that a 58K-like protein is present in the calli of Arabidopsis thaliana and Hypericum perforatum. The results of immuno-electron microscopy showed that the 58K-like protein was located in the cisternae of Golgi bodies, secretory vesicles, multi-vesicular bodies, cell walls and vacuoles in callus of Arabidopsis thaliana, suggesting that the multi-vesicular bodies may be originated from Golgi bodies and function as a transporter carrying substances synthesized in Golgi bodies to cell walls and vacuoles. It seems that multi-vesicular bodies have a close relationship with the development of the cell wall and vacuole. The possible secretory pathways of multi-vesicular bodies might be in exocytosis, in which multi-vesicular bodies carry sub-stances to the cell wall for its construction, and in endocytosis, in which multi-vesicular bodies carry substances to the vacuole for its development, depending on what they carry and where the materials are transported. We hence propose that there is more than one pathway for the secretion of multi-vesicular bodies. In addition, our results provided a paradigm that a plant molecule, such as the 58k-like protein in callus of Arabidopsis thaliana, can be detected using a cross-reactive monoclonal antibody induced by an animal protein, and illustrate the existence of analog molecules in both animal and plant kingdoms.     

Polo-like kinase 3 is Golgi localized and involved in regulating Golgi fragmentation during the cell cycle

The Golgi apparatus undergoes extensive fragmentation during mitosis in animal cells. Protein kinases play a critical role during fragmentation of the Golgi apparatus. We reported here that Polo-like kinase 3 (Plk3) may be an important mediator during Golgi breakdown. Specifically, Plk3 was concentrated at the Golgi apparatus in HeLa and A549 cells during interphase. At the onset of mitosis, Plk3 signals disintegrated and redistributed in a manner similar to those of Golgi stacks. Nocodazole activated Plk3 kinase activity, correlating with redistribution of Plk3 signals and Golgi fragmentation. In addition, treatment with brefeldin A (BFA), a Golgi-specific poison, also resulted in disappearance of concentrated Plk3 signals. Plk3 interacted with giantin, a Golgi-specific protein. Expression of Plk3, but not the kinase-defective Plk3 (Plk3(K52R)), resulted in significant Golgi breakdown. Given its role in cell cycle progression, Plk3 may be a protein kinase involved in regulation of Golgi fragmentation during the cell cycle.     

Localization of Golgi 58K protein (formiminotransferase cyclodeaminase) to the centrosome

In vertebrate cells, the centrosome consists of a pair of centrioles and surrounding pericentriolar material. Using anti-Golgi 58K protein antibodies that recognize formiminotransferase cyclodeaminase (FTCD), we investigated its localization to the centrosome in various cultured cells and human oviductal secretory cells by immunohistochemistry. In addition to the Golgi apparatus, FTCD was localized to the centrosome, more abundantly around the mother centriole. The centrosome localization of FTCD continued throughout the cell cycle and was not disrupted after Golgi fragmentation, which was induced by colcemid and brefeldin A. Centriole microtubules are polyglutamylated and stable against tubulin depolymerizing drugs. FTCD in the centrosome may be associated with polyglutamylated residues of centriole microtubules and may play a role in providing centrioles with glutamate produced by cyclodeaminase domains of FTCD.     

Identification and characterization of AtCASP,a plant transmembrane Golgi matrix protein

Golgins are a family of coiled-coil proteins that are associated with the Golgi apparatus. They are necessary for tethering events in membrane fusion and may act as structural support for Golgi cisternae. Here we report on the identification of an Arabidopsis golgin which is a homologue of CASP, a known transmembrane mammalian and yeast golgin. Similar to its homologues, the plant CASP contains a long N-terminal coiled-coil region protruding into the cytosol and a C-terminal transmembrane domain with amino acid residues which are highly conserved across species. Through fluorescent protein tagging experiments, we show that plant CASP localizes at the plant Golgi apparatus and that the C-terminus of this protein is sufficient for its localization, as has been shown for its mammalian counterpart. In addition, we demonstrate that the plant CASP is able to localize at the mammalian Golgi apparatus. However, mutagenesis of a conserved tyrosine in the transmembrane domain revealed that it is necessary for ER export and Golgi localization of the Arabidopsis CASP in mammalian cells, but is not required for its correct localization in plant cells. These data suggest that mammalian and plant cells have different mechanisms for concentrating CASP in the Golgi apparatus.†These authors have contributed equally to the work     

Immunohistochemical localization of collagen type XI alpha1 and alpha2 chains in human colon tissue.

In previous studies, collagen XI mRNA has been detected in colon cancer, but its location in human colon tissue has not been determined. The heterotrimeric collagen XI consists of three alpha chains. While it is known that collagen XI plays a regulatory role in collagen fibril formation, its function in the colon is unknown. The characterization of normal human colon tissue will allow a better understanding of the variance of collagen XI in abnormal tissues. Grossly normal and malignant human colon tissue was obtained from pathology archives. Immunohistochemical staining with a 58K Golgi marker and alpha1(XI) and alpha2(XI) antisera was used to specifically locate their presence in normal colon tissue. A comparative bright field microscopic analysis showed the presence of collagen XI in human colon. The juxtanuclear, dot-like collagen XI staining in the Golgi apparatus of goblet cells in normal tissue paralleled the staining of the 58K Golgi marker. Ultra light microscopy verified these results. Staining was also confirmed in malignant colon tissue. This study is the first to show that collagen XI is present in the Golgi apparatus of normal human colon goblet cells and localizes collagen XI in both normal and malignant tissue. Although the function of collagen XI in the colon is unknown, our immunohistochemical characterization provides the foundation for future immunohistopathology studies of the colon.     

Reversible dissociation of the plant golgi apparatus by brefeldin A

Summary— The effects of the drug Brefeldin A, shown to block the translocation of proteins between the endoplasmic reticulum and the Golgi apparatus in animal cells, were studied on different plant cell systems. In suspension culture cells and root tissues, the Golgi aparatus was affected by Brefeldin A treatments resulting in distortion and dissociation of the Golgi stacks, coupled with appearance of numerous vesicles in the cytoplasm. This process was reversible. Therefore, Brefeldin A provides a powerful tool with which to study Golgi dynamics and function in plant as well as in animal cells.     

Detection and localization of pectin methylesterase isoforms in pollen tubes of Nicotiana tabacum L.

Pectin methylesterases (PMEs) were detected in tobacco ( Nicotiana tabacum) pollen tubes grown in vitro. Seven PME isoforms exhibiting a wide isoelectric-point (pI) range (5.3-9.1) were found in crude extracts of pollen tubes. These isoforms were mainly retrieved in supernatants after low- and high-speed separation of the crude extract. Two isoforms, with pIs 5.5 and 7.3 and molecular weight about 158 kDa, were detected by immunoblotting with anti-flax PME antiserum. Localization of pectins and PME isoforms in pollen tubes was investigated by immunogold labelling with JIM5 monoclonal antibodies and anti-flax PME antiserum, respectively. In germinated pollen grains, two PME isoforms were mainly detected in the exine, Golgi apparatus and secretory vesicles. In pollen tubes the same two PME isoforms were distributed along the outer face of the plasma membrane in the vicinity of the inner layer of the cell wall, in the Golgi and around secretory vesicles. In pollen grains, PME isoforms were, in some cases, mixed with acidic pectins in proximity to the outer surface of the plasma membrane. In pollen tubes the presence of PMEs inside secretory vesicles carrying esterified pectins supports the hypothesis that, during pollen tube growth, PMEs could be transferred by secretory vesicles in a precursor form and be activated at the tip where exocytosis takes place.     

Arf1 GTPase plays roles in the protein traffic between the endoplasmic reticulum and the Golgi apparatus in tobacco and Arabidopsis cultured cells

Arf GTPases are known to be key regulators of vesicle budding in various steps of membrane traffic in yeast and animal cells. We cloned the Arabidopsis Arf1 homologue, AtArf1, and examined its function. AtArf1 complements yeast arf1 arf2 mutants and its GFP-fusion is localized to the Golgi apparatus in plant cells like its animal counterpart. The expression of dominant negative mutants of AtArf1 in tobacco and Arabidopsis cultured cells affected the localization of co-expressed GFP-tagged proteins in a variety of ways. AtArf1 Q71L and AtArf1 T31N, GTP- and GDP-fixed mutants, respectively, changed the localization of a cis-Golgi marker, AtErd2-GFP, from the Golgi apparatus to the endoplasmic reticulum but not that of GFP-AtRer1B or GFP-AtSed5. GFP-AtRer1B and GFP-AtSed5 were accumulated in aberrant structures of the Golgi by AtArf1 Q71L. A soluble vacuolar protein, sporamin-GFP, was also located to the ER by AtArf1 Q71L. These results indicate that AtArf1 play roles in the vesicular transport between the ER and the Golgi and in the maintenance of the normal Golgi organization in plant cells.     

MALE GAMETOPHYTE DEFECTIVE 2, Encoding a Sialyltransferase-like Protein, is Required for Normal Pollen Germination and Pollen Tube Growth in Arabidopsis

Sialyltransferases (SiaTs) exist widely in vertebrates and play important roles in a variety of biological processes. In plants, several genes have also been identified to encode the proteins that share homology with the vertebrate SiaTs. However, very little is known about their functions in plants. Here we report the identification and characterization of a novel Arabidopsis gene, MALE GAMETOPHYTE DEFECTIVE 2 [MGP2) that encodes a sialyltransferase-like protein. MGP2 was expressed in all tissues including pollen grains and pollen tubes. The MGP2 protein was targeted to Golgi apparatus. Knockout of MGP2 significantly inhibited the pollen germination and retarded pollen tube growth in vitro and in vivo, but did not affect female gametophytic functions. These results suggest that the sialyltransferase-like protein MGP2 is important for normal pollen germination and pollen tube growth, giving a novel insight into the biological roles of the sialyltransferase-like proteins in plants.     

Membrane flow in plants: Fractionation of growing pollen tubes of tobacco by preparative free-flow electrophoresis and kinetics of labeling of endoplasmic reticulum and golgi apparatus with [3H]leucine

Summary Tobacco (Nicotiana tabacum L.) pollen, germinated 4 hours in suspension culture, was labeled with radioactive leucine and fractionated into constituent membranes by the technique of preparative free-flow electrophoresis. Tubes were ruptured by sonication directly into the electrophoresis buffer. Unfortunately, the Golgi apparatus of the rapidly elongating pollen tubes did not survive the sonication step. However, it was possible to obtain useful fractions of endoplasmic reticulum and mitochondria. To obtain Golgi apparatus, glutaraldehyde was added to the homogenization buffer during sonication. Plasma membrane, which accounted for only about 3% of the total membrane of the homogenates as determined by staining with phosphotungstate at low pH, was obtained in insufficient quantity and fraction purity to permit analysis. Results show rapid incorporation of [³H]leucine into endoplasmic reticulum followed by rapid chase out. The half-time for loss of radioactivity from the pollen tube endoplasmic reticulum was about 10 minutes. Concomitant with the loss of radioactivity from endoplasmic reticulum, the Golgi apparatus fraction was labeled reaching a maximum 20 minutes post chase. The findings suggest flow of membranes from endoplasmic reticulum to the Golgi apparatus during pollen tube growth.     

Chondroptosis: An immunohistochemical study of apoptosis and Golgi complex in chondrocytes from human osteoarthritic cartilage

The Golgi complex is thought to play an important role in the apoptotic process of osteoarthritic (OA) chondrocytes. However, the exact relationship between modifications of the Golgi complex and apoptosis in human OA cartilage requires to be established. We compared the patterns and immunolabeling intensities for anti-Golgi 58 K protein with apoptosis markers such as TUNEL and caspase-2L in OA cartilage removed from patients during knee total replacement surgery. We observed important modifications in labeling of the Golgi 58 K protein in OA chondrocytes compared with normal cell. Immunohistochemical analysis revealed co-localization between 58 K protein and caspase-2L, suggesting that this enzyme was localized in Golgi complex of OA chondrocytes. In addition, these cells labeled positive with the TUNEL technique, but in different proportions to caspase-2L. Our results support the concept, previously reported, that apoptosis in OA cartilage (chondroptosis) might be a variant of the classical apoptosis.     

BFA‐induced compartments from the Golgi apparatus and trans‐Golgi network/early endosome are distinct in plant cells

Brefeldin A (BFA) is a useful tool for studying protein trafficking and identifying organelles in the plant secretory and endocytic pathways. At low concentrations (5–10 μg ml^?1), BFA caused both the Golgi apparatus and trans‐Golgi network (TGN), an early endosome (EE) equivalent in plant cells, to form visible aggregates in transgenic tobacco BY‐2 cells. Here we show that these BFA‐induced aggregates from the Golgi apparatus and TGN are morphologically and functionally distinct in plant cells. Confocal immunofluorescent and immunogold electron microscope (EM) studies demonstrated that BFA‐induced Golgi‐ and TGN‐derived aggregates are physically distinct from each other. In addition, the internalized endosomal marker FM4‐64 co‐localized with the TGN‐derived aggregates but not with the Golgi aggregates. In the presence of the endocytosis inhibitor tyrphostin A23, which acts in a dose‐ and time‐dependent manner, SCAMP1 (secretory carrier membrane protein 1) and FM4‐64 are mostly excluded from the SYP61‐positive BFA‐induced TGN aggregates, indicating that homotypic fusion of the TGN rather than de novo endocytic trafficking is important for the formation of TGN/EE‐derived BFA‐induced aggregates. As the TGN also serves as an EE, continuously receiving materials from the plasma membrane, our data support the notion that the secretory Golgi organelle is distinct from the endocytic TGN/EE in terms of its response to BFA treatment in plant cells. Thus, the Golgi and TGN are probably functionally distinct organelles in plants.     

Immunocytochemical evidence for the involvement of golgi apparatus in the deposition of seed lectin ofBauhinia purpurea (Leguminosae)

Summary The seed lectin of the tree legume,Bauhinia purpurea alba, was localized by electron microscopic immunocytochemistry. The pattern of lectin deposition and site of intracellular localization was examined in mid- to late-maturation seeds. The seed tissue was embedded in Lowicryl K4M, the use of which with seed tissues is discussed. Immunocytochemical labeling was accomplished with colloidal gold coupled to a second antibody. The immunocytochemical reaction was specific and sensitive. Protein bodies, Golgi apparatus and Golgi secretion vesicles were densely labeled. Golgi apparatus was oriented such that Golgi secretion vesicles were in close proximity to the protein bodies. The entire Golgi apparatus was labeled with no concentration gradient across the Golgi stack. These observations indicate that the final site of lectin deposition is the protein body, and that the Golgi apparatus plays an essential role in the deposition process.     

Effect of brefeldin A on the structure of the Golgi apparatus and on the synthesis and secretion of proteins and polysaccharides in sycamore maple (Acer pseudoplatanus) suspension-cultured cells.

Brefeldin A (BFA), a specific inhibitor of Golgi-mediated secretion in animal cells, has been used to study the organization of the secretory pathway and the function of the Golgi apparatus in plant cells. To this end, we have employed a combination of electron microscopical, immunocytochemical, and biochemical techniques to investigate the effects of this drug on the architecture of the Golgi apparatus as well as on the secretion of proteins and complex cell wall polysaccharides in sycamore maple (Acer pseudoplatanus) suspension-cultured cells. We have used 2.5 and 7.5 micrograms/mL of BFA, which is comparable to the 1 to 10 micrograms/mL used in experiments with animal cells. Electron micrographs of high-pressure frozen and freeze-substituted cells show that although BFA causes swelling of the endoplasmic reticulum cisternae, unlike in animal cells, it does not induce the disassembly of sycamore maple Golgi stacks. Instead, BFA induces the formation of large clusters of Golgi stacks, an increase in the number of trans-like Golgi cisternae, and the accumulation in the cytoplasm of very dense vesicles that appear to be derived from trans Golgi cisternae. These vesicles contain large amounts of xyloglucan (XG), the major hemicellulosic cell wall polysaccharide, as shown by immunocytochemical labeling with anti-XG antibodies. All of these structural changes disappear within 120 min after removal of the drug. In vivo labeling experiments using [3H]leucine demonstrate that protein secretion into the culture medium, but not protein synthesis, is inhibited by approximately 80% in the presence of BFA. In contrast, the incorporation of [3H]fucose into N-linked glycoproteins, which occurs in trans-Golgi cisternae, appears to be affected to a greater extent than the incorporation of [3H]xylose, which has been localized to medial Golgi cisternae. BFA also affects secretion of complex polysaccharides as evidenced by the approximate 50% drop in incorporation of [3H]xylose and [3H]fucose into cell wall hemicelluloses. Taken together, these findings suggest that at concentrations of 2.5 to 7.5 mu g/mL BFA causes the following major changes in the secretory pathway of sycamore maple cells: (a) it inhibits the transport of secretory proteins to the cell surface by about 80% and of hemicelluloses by about 50%; (b) it changes the patterns of glycosylation of N-linked glycoproteins and hemicelluloses; (c) it reduces traffic between trans Golgi cisternae and secretory vesicles; (d) it produces a major block in the transport of XG-containing, dense secretory vesicles to the cell surface; and (e) it induces the formation of large aggregates of Golgi apparatus of plant and animal cels share many functional and structural characteristics, the plant Golgi apparatus possesses properties that make its response to BFA unique.     

ARL1 Plays a Role in the Binding of the GRIP Domain of a Peripheral Matrix Protein to the Golgi Apparatus in Plant Cells

ARF GTPases play a central role in regulating membrane dynamics and protein transport in eukaryotic cells. ARF-like (ARL) proteins are close relatives of the ARF regulators of vesicular transport, but their function in plant cells is poorly characterized. Here, by means of live cell imaging and site-directed mutagenesis, we have investigated the cellular function of the plant GTPase ARL1. We provide direct evidence for a role of this ARL family member in the association of a plant golgin with the plant Golgi apparatus. Our data reveal the existence of key residues within the conserved GRIP-domain of the golgin and within the GTPase ARL1 that are central to ARL1–GRIP interaction. Mutations of these residues abolish the interaction of GRIP with the GTP-bound ARL1 and induce a redistribution of GRIP into the cytosol. This indicates that the localization of GRIP to the Golgi apparatus is strongly influenced by the interaction of GRIP with Golgi-localized ARL1. Our results assign a cellular role to a member of the Arabidopsis ARL family in the plant secretory pathway and propose mechanisms for localization of peripheral golgins to the plant Golgi apparatus. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Role of Xklp3, a Subunit of the Xenopus Kinesin II Heterotrimeric Complex,in Membrane Transport between the Endoplasmic Reticulum and the Golgi Apparatus

The function of the Golgi apparatus is to modify proteins and lipids synthesized in the ER and sort them to their final destination. The steady-state size and function of the Golgi apparatus is maintained through the recycling of some components back to the ER. Several lines of evidence indicate that the spatial segregation between the ER and the Golgi apparatus as well as trafficking between these two compartments require both microtubules and motors. We have cloned and characterized a new Xenopus kinesin like protein, Xklp3, a subunit of the heterotrimeric Kinesin II. By immunofluorescence it is found in the Golgi region. A more detailed analysis by EM shows that it is associated with a subset of membranes that contain the KDEL receptor and are localized between the ER and Golgi apparatus. An association of Xklp3 with the recycling compartment is further supported by a biochemical analysis and the behavior of Xklp3 in BFA-treated cells. The function of Xklp3 was analyzed by transfecting cells with a dominant-negative form lacking the motor domain. In these cells, the normal delivery of newly synthesized proteins to the Golgi apparatus is blocked. Taken together, these results indicate that Xklp3 is involved in the transport of tubular-vesicular elements between the ER and the Golgi apparatus.     

Golgi apparatus immunolocalization of endomannosidase suggests post-endoplasmic reticulum glucose trimming: implications for quality control

Trimming of N-linked oligosaccharides by endoplasmic reticulum (ER) glucosidase II is implicated in quality control of protein folding. An alternate glucosidase II-independent deglucosylation pathway exists, in which endo-alpha-mannosidase cleaves internally the glucose-substituted mannose residue of oligosaccharides. By immunogold labeling, we detected most endomannosidase in cis/medial Golgi cisternae (83.8% of immunogold labeling) and less in the intermediate compartment (15.1%), but none in the trans-Golgi apparatus and ER, including its transitional elements. This dual localization became more pronounced under 15 degrees C conditions indicative of two endomannosidase locations. Under experimental conditions when the intermediate compartment marker p58 was retained in peripheral sites, endomannosidase was redistributed to the Golgi apparatus. Double immunogold labeling established a mutually exclusive distribution of endomannosidase and glucosidase II, whereas calreticulin was observed in endomannosidase-reactive sites (17.3% in intermediate compartment, 5.7% in Golgi apparatus) in addition to the ER (77%). Our results demonstrate that glucose trimming of N-linked oligosaccharides is not limited to the ER and that protein deglucosylation by endomannosidase in the Golgi apparatus and intermediate compartment additionally ensures that processing to mature oligosaccharides can continue. Thus, endomannosidase localization suggests that a quality control of N-glycosylation exists in the Golgi apparatus.