Structure of Golgi apparatus

Summary Golgi apparatus (GA) of eukaryotic cells consist of one or more stacks of flattened saccules (cisternae) and an array of fenestrae and tubules continuous with the peripheral edges of the saccules. Golgi apparatus also are characterized by zones of exclusion that surround each stack and by an assortment of vesicles (or vesicle buds) associated with both the stacks and the peripheral tubules of the stack cisternae. Each stack (sometimes referred to as Golgi apparatus, Golgi complex, or dictyosome) is structurally and functionally polarized, reflecting its role as an intermediate between the endoplasmic reticulum, the cell surface, and the lysosomal system of the cell. There is probably only one GA per cell, and all stacks of the GA appear to function synchronously. All Golgi apparatus are involved in the generation and movement of product and membrane within the cell or to the cell exterior, and these functions are often reflected as structural changes across the stacks. For example, in plants, both product and membrane appear to maturate from the cis to the trans poles of the stacks in a sequential, or serial, manner. However, there is also strong ultrastructural evidence in plants for a parallel input to the stack saccules, probably through the peripheral tubules. The same modes of functioning probably also occur in animal GA; although here, the parallel mode of functioning almost surely predominates. In some cells at least, GA stacks give rise to tubular-vesicular structures that resemble the trans Golgi network. Rudimentary GA, consisting of tubular-vesicular networks, have been identified in fungi and may represent an early stage of GA evolution.     

Targeting of proteins to the Golgi apparatus

The Golgi apparatus maintains a highly organized structure in spite of the intense membrane traffic which flows into and out of this organelle. Resident Golgi proteins must have localization signals to ensure that they are targeted to the correct Golgi compartment and not swept further along the secretory pathway. There are a number of distinct groups of Golgi membrane proteins, including glycosyltransferases, recyclingtrans-Golgi network proteins, peripheral membrane proteins, receptors and viral glycoproteins. Recent studies indicate that there are a number of different Golgi localization signals and mechanisms for retaining proteins to the Golgi apparatus. This review focuses on the current knowledge in this field.     

The Golgi apparatus in epidermal mucoid and ellipsoid-vacuolate cells ofAeolidia papillosa andCoryphella rufibranchialis (Nudibranchia)

Summary The epidermal cell layer of the apical end of the ceras was investigated in two species of aeolid nudibranchs. Based on cellular inclusions, mostly two cell types were found: mucoid and ellipsoid-vacuolate cells. Mucoid cells ofCoryphella rufibranchialis have large heterogeneous and fibrillar secretory granules whereas inAeolidia papillosa, the granules are homogeneous, but vary in electron density from one cell to another. Ellipsoid-vacuolate cells contained large quantities of small vacuoles with an included ellipsoidal structure. Both species contained very numerous ellipsoid-vacuolate cells. Secretory granules and ellipsoid-vacuoles appear to arise from the Golgi apparatus and these contents stain with PAS, suggesting a polysaccharide composition. Mucoid cells contained both secretory granules and ellipsoid-vacuoles which may arise from the same Golgi apparatus.     

Growth kinetics of the Golgi apparatus during the cell cycle in onion root meristems

In onion root meristems, the number of dictyosomes per cell shows a kinetics of growth strongly related to the cell cycle. During the interphase of steady-state proliferative cells, the volume density and numerical density of the Golgi apparatus decrease to reach minimum values in late-interphase cells, characterized by their greatest length. This pattern is also found in the total volume occupied by Golgi apparatus. Once in mitosis, the above-mentioned parameters begin to increase reaching maximum mean values in telophase. After the experimental uncoupling of chromosome and growth cycles by presynchronization with hydroxyurea, we found a similar behaviour pattern in the Golgi apparatus: decreasing values during interphase and a triggering of Golgi-apparatus growth in prophase independently of the bigger cell sizes reached in mitosis as an effect of pretreatment with hydroxyurea. These results indicate a cyclic kinetics of this subcellular component in higher-plant meristems, coupled with early mitotic events.     

Post Golgi apparatus structures and membrane removal in plants

Summary In nongrowing secretory cells of plants, large quantities of membrane are transferred from the Golgi apparatus to the plasma membrane without a corresponding increase in cell surface area or accumulation of internal membranes. Movement and/or redistribution of membrane occurs also in trans Golgi apparatus cisternae which disappear after being sloughed from the dictyosome, and in secretory vesicles which lose much of their membrane in transit to the cell surface. These processes have been visualized in freeze-substituted corn rootcap cells and a structural basis for membrane loss during trafficking is seen. It involves three forms of coated membranes associated with the trans parts of the Golgi apparatus, with cisternae and secretory vesicles, and with plasma membranes. The coated regions of the plasma membrane were predominantly located at sites of recent fusion of secretory vesicles suggesting a vesicular mechanism of membrane removal. The two other forms of coated vesicles were associated with the trans cisternae, with secretory vesicles, and with a post Golgi apparatus tubular/vesicular network not unlike the TGN of animal cells. However, the trans Golgi network in plants, unlike that in animals, appears to derive directly from the trans cisternae and then vesiculate. The magnitude of the coated membrane-mediated contribution of the endocytic pathway to the formation of the TGN in rootcap cells is unknown. Continued formation of new Golgi apparatus cisternae would be required to maintain the relatively constant form of the Golgi apparatus and TGN, as is observed during periods of active secretion.     

The Golgi apparatus in developing endosperm of wheat (Triticum aestivum L.)

The ultrastructure and distribution of the Golgi apparatus in developing wheat endosperm was investigated using a zinc iodide-osmium tetroxide staining complex in conjunction with low and high voltage electron microscopy. Dictyosomes were numerous in starchy endosperm and aleurone at 15 days after anthesis, and during the period of rapid storage protein deposition 25 d after anthesis. Fewer dictyosomes were seen in maturing endosperm. Two types of vesicles were associated with the dictyosomes; small, heavily-stained vesicles were sited at the ends of fine tubules which extend from the cisternae, and larger less-stained vesicles were associated with the periphery of the cisternae. Stereo-pairs of micrographs up to 1 m thick were taken to demonstrate the interconnections between cisternal and tubular endoplasmic reticulum. Elements of tubular ER were closely associated with dictyosomes, but connections were not observed. These results are discussed in relation to the transport of endosperm storage proteins from their site of synthesis on the cisternal ER to their site of storage, the protein bodies.     

The endomembrane system and mechanism of membrane flow in the green alga,Gloeomonas kupfferi (Volvocales,Chlorophyta) I. An ultrastructural analysis

Summary The endomembrane system of the chlamydomonad flagellate,Gloeomonas kupfferi (Chlorophyta), is complex. It consists of a proliferating ER network, a perinuclear complex of 14–18 dictyosomes and 8–12 vacuoles and an anterior contractile vacuole complex. The ER network extends from the nuclear envelope outwards, ensheafhs a dictyosome, extends out through a lobe of the chloroplast and terminates in the thin zone of peripheral cytoplasm between the chloroplast and plasmamembrane. The individual dictyosome is polar with distinct cis- and trans-faces. The cis-face is closely associated with transition vesicles emerging from the adjacent ER. Large vesicles emerge from peripheral swellings of terminal cisternae. The dictyosome-associated ER is connected to the peripheral vacuolar system. During cell division and cytokinesis, changes in the endomembrane system occur. Dictyosomes divide and quickly separate to form perinuclear complexes around the daughter nuclei. Each dictyosome undergoes morphological changes during this wall precursor-producing stage. ER lines the furrow zone and is closely associated with phycoplast microtubules. A discussion of the endomembrane system in membrane flow mechanics is provided.Abbreviations ER endoplasmic reticulum - OsFeCN Osmium ferricyanide     

Effects of brefeldin A on the Golgi apparatus, the nuclear envelope, and the endoplasmic reticulum in a green alga,Scenedesmus acutus

Summary The effects of brefeldin A (BFA) on the structure of the Golgi apparatus, the nuclear envelope, and the endoplasmic reticulum (ER), and on the thiamine pyrophosphatase (TPPase) activity in these organelles were examined in a green alga,Scenedesmus acutus, to obtain evidence for the existence of a retrograde transport from the Golgi apparatus to the ER via the nuclear envelope. InScenedesmus, Golgi bodies are situated close to the nuclear envelope throughout the cell cycle and receive the transition vesicles not directly from the ER, but from the nuclear envelope. BFA induced the disassembly of Golgi bodies and an increase in the ER cisternae at the trans-side of decomposed Golgi bodies in interphase cells and multinuclear cells before septum formation. The accumulated ER cisternae connected to the nuclear envelope at one part. TPPase activity was detected in all cisternae of Golgi bodies, but not in the nuclear envelope or the ER in nontreated cells. On the contrary, in BFA-treated cells, TPPase activity was detected in the nuclear envelope and the ER in addition to the decomposed Golgi bodies. When septum-forming cells were treated with BFA, the disassembly of Golgi bodies was less than that in interphase cells, and TPPase activity was detected in the Golgi cisternae but not in the nuclear envelope or the ER. These results suggest mat BFA blocks the anterograde transport from the nuclear envelope to the Golgi bodies but does not block the retrograde transport from the Golgi bodies to the nuclear envelope in interphase and multinuclear cells.Abbreviations BFA brefeldin A - ER endoplasmic reticulum - TPPase thiamine pyrophosphatase     

Changes in the activity of the Golgi apparatus during the cell cycle in antheridial filaments ofChara vulgaris L.

Summary The number of dictyosomes found in one central cell section in antheridial filaments ofChara vulgaris increases proportionally to the cell length during interphase. The activity of Golgi apparatus was expressed by a number of Golgi vesicles surrounding a single dictyosome. These vesicles are most numerous during mitosis and cytokinesis,i.e., prior to and during cell plate formation. In the middle and late S phase the number of Golgi vesicles decreases by about 25%; subsequently, during the early and middle G₂, it increases again. At the end of the G₂ phase, Golgi vesicles are the scarcest.The increase in the number of Golgi vesicles during the G₂ phase coincides with the period of intense cellular elongation, and, thus, it is probably related to the enhanced synthesis of cell wall components.Coated vesicles are most numerous in prophase, metaphase, and early telophase, and during interphase in both late S and G₂ phase. It was found that the number of coated vesicles is proportional to the degree of condensation of nuclear chromatin.This work was supported by the Polish Academy of Sciences within the project 09.7.3.1.4.     

The Golgi apparatus ofPhytophthora cinnamomi makes three types of secretory or storage vesicles concurrently

Summary The formation of three types of vesicles in the oomycetePhytophthora cinnamomi was investigated using ultrastructural and immunocytochemical techniques. All three vesicles are synthesised at the same time; one type serves a storage role; the others undergo regulated secretion. A monoclonal antibody Lpv-1 that is specific for glycoproteins contained in the storage vesicles labelled the endoplasmic reticulum (ER), elements in the transition region between ER and Golgi stack, and cis, medial and trans Golgi cisternae. Cpa2, a monoclonal antibody specific for glycoproteins contained within secretory dorsal vesicles labelled the transition region, cis cisternae and a trans-Golgi network. Vesicles possessing a structure characteristic of mature secretory ventral vesicles were observed in close association with the trans face of Golgi stacks. The results suggest that all three vesicles are formed by the Golgi apparatus. Double immunogold labelling with Lpv-1 and Cpa-2 showed that these two sets of glycoproteins occurred within the same Golgi cisternae, indicating that both products pass through and are sorted concurrently within a single Golgi stack.     

The Golgi apparatus in parasitic protists

This review summarizes the current reports on the Golgi apparatus of parasitic protists. Numerous recent publications have demonstrated that studies on intracellular traffic in parasites essentially advanced our knowledge on the Golgi structure and function, which has been traditionally based on research on yeast and mammalian cultured cells. It has been reported that the parasitic lifestyle determines the functional and structural peculiarities of the secretory systems in unrelated groups of unicellular parasites that make them different from those in mammalian and yeast cells. This review covers the best-studied protists, predominantly those of high medical importance, belonging to the following taxa: Parabasalia (Trichomonas), Diplomonada (Giardia), Entamoebidae (Entamoeba), parasitic Alveolata of the phyllum Apicomplexa (Toxoplasma, Plasmodium), and Kinetoplastida (Trypanosoma, Leishmania). The morphology of the Golgi organelle in eukaryotes from various taxonomic groups has been compared. Within three of the six highest taxa of Eukaryota (Adl et al., 2005) a minimum of eight groups are represented by species lacking Golgi dictiosomes. However, biochemical and/or molecular (genomic) evidence indicate that an organelle with the functions of the Golgi was present in every lineage of eukaryotes studied thus far. Loss of the Golgi organelle is a secondary event as proven by identification of Golgi genes in the genomes of Golgi-lacking lineages. The loss might have occurred independently several times in evolution. Neither the number of stacks, nor the size of the organelle correlates with the intensity of secretion or the position of the species on the evolutionary tree (in terms of presumably early/lately diverged lineages).     

1998: The centenary of the discovery of the Golgi apparatus

1998 is the year of the centenary of the discovery of the Golgi apparatus. This event is considered in its historical context: the first cell theory of 1838–1839, the first polemics in cytology and the research on the cell organelles at the turn of the century. The first approaches to clarify the physiological significance of the apparatus is traced from Golgi (1909) to Bowen (1929).     

Formation of wheat protein bodies: Involvement of the Golgi apparatus in gliadin transport

Developing wheat (Triticum aestivum L.) endosperm was examined using ultrathin sections prepared from tissues harvested at 5, 9, 16 and 25 d after flowering. Protein bodies were evident by 9 d and displayed a variety of membranous structures and inclusions. The Golgi apparatus was a prominent organelle at all stages, and by 9 d was associated with small electron-dense inclusions. By immunocytochemical techniques, gliadin (wheat prolamine) was localized within these vesicles and in homogeneous regions of protein bodies, but not in the lumen of the rough endoplasmic reticulum. The protein bodies appear to enlarge by fusion of smaller protein bodies resulting in larger, irregular-shaped organelles. The affinity of the Golgi-derived vesicles for gliadin-specific probes during the period of maximal storage-protein synthesis and deposition indicates that this organelle includes the bulk, if not all, of the gliadin produced. The involvement of the Golgi apparatus in the packaging of gliadins into protein bodies indicates a pathway which differs from the mode of prolamine deposition in other cereals such as maize, rice and sorghum, and resembles the mechanism employed for the storage of rice glutelin and legume globulins.Abbreviations ER endoplasmic reticulum - IgG immunoglobulin G - DAF days after flowering     

The endomembrane system and mechanism of membrane flow in the green alga,Gloeomonas kupfferi (Volvocales,Chlorophyta) II. A cytochemical analysis

Summary Cytochemical analysis of the endomembrane system of the chlamydomonad flagellate,Gloeomonas kupfferi (Chlorophyta), reveals distinct compartmentalization. Phosphatase localization shows that: IDPase is located throughout all cisternae of the dictyosome and vesicles associated with the contractile vacuole. Other alkaline phosphatases like TPPase, ATPase and ITPase were localized within the trans-face cisternae and vesicles of the contractile vacuole. IMPase was localized at the plasmamembrane and not within the endomembrane system. Acid phosphatases, incl. CMPase, NADPase and -glycerophosphatase, were localized in vesicles emerging from the central terminus of the trans-face of the dictyosome and in the peripheral vacuolar network. Silver proteinate labeling was noted in the dictyosome, contractile vacuole and on the anterior plasmamembrane. A summary of endomembrane compartmentalization and a putative interpretation of membrane flow and economy are presented.Abbreviations ER endoplasmic reticulum - IDPase inosine 5-diphosphatase - ITPase inosine 5-triphosphatase - ATPase adenosine 5-triphosphatase - TPPase thiamine pyrophosphatase - CMPase cytidine 5-monophosphatase - NADPase -nicotinamide adenine diphosphatase - AcPase acid phosphatase     

Phospholipase D in the Golgi apparatus

Phospholipase D has long been implicated in vesicle formation and vesicular transport through the secretory pathway. The Golgi apparatus has been shown to exhibit a plethora of mechanisms of vesicle formation at different stages to accommodate a wide variety of cargo. Phospholipase D has been found on the Golgi apparatus and is regulated by ADP-ribosylation factors which are themselves regulators of vesicle trafficking. Moreover, the product of phospholipase D activity, phosphatidic acid, as well as its degradation product diacylglycerol, have been implicated in vesicle fission and fusion events. Here we summarize recent advances in the understanding of the role of phospholipase D at the Golgi apparatus.     

Cell biology of the plant Golgi apparatus

The higher plant Golgi apparatus, comprising many individual stacks of membrane bounded cisternae, is one of the most enigmatic of the cytoplasmic organelles. Not only can the stacks receive material from the endoplasmic reticulum, process it and target it to the correct cellular destination, but they can also synthesise and export complex carbohydrates and lipids and most likely act as one end point of the endocytic pathway. In many cells such processing and sorting can take place while the stacks are moving within the cytoplasm and, remarkably, the organelle manages to retain its structural integrity. This review considers some of the latest data and views on transport both to and from the Golgi and the mechanisms by which such activity is regulated.     

Organization and composition of the striated roots supporting the Golgi apparatus,the so-called parabasal apparatus,in parabasalid flagellates

Summary— In parabasalid flagellates, trichomonads and hypermastigids, the stack of cisternae of the Golgi apparatus are supported by striated roots attached to the basal bodies of flagella forming the so-called parabasal apparatus. Monoclonal antibodies raised for several trichomonad species, Monocercomonas, Trichomonas and Tetratrichomonas, label the parabasal fibre in immunofluorescence or immunogold staining and protein bands in immunoblotting. Several antibodies cross-react between trichomonad species, and one of them labels the homologous parabasal fibre in the hypermastigids: Trichonympha, Joenia, Pseudotrichonympha and Holomastigotoides. Considering the molecular mass range of the labelled proteins (100–135 kDa) and the lack of antibody cross-reactivity with the striated root proteins (centrin, assemblin, kinetodesmal protein, ciliary root proteins of epithelial ciliated cells) of other organisms, these proteins recognized by these antibodies seem to represent a new class of protein forming striated roots. The occurrence and significance of parabasal organization in eukaryogenesis is discussed.     

Changes in the secretory activity of the Golgi apparatus during the cell cycle in root tips of maize (Zea Mays L.)

Epidermal cells of maize roots were studied to determine the distribution of Golgi apparatus-derived secretory vesicles in various stages of cell division. The following conclusions were reached: 1) The pattern of Golgi apparatus secretion varies with the cell cycle. 2) Large numbers of secretory vesicles are incorporated into the cell plate. 3) Secretory vesicles from the Golgi apparatus are incorporated primarily in walls undergoing expansion. 4) Secretory vesicles are smaller during mitosis and the first part of cytokinesis than they are during interphase. 5) Secretory vesicles account for at least 12–23% of cell-plate plasma membrane and an estimated 25% of cell-plate volume.     

Golgi apparatus isolation and use in cell-free systems

Summary Recent advances in understanding the molecular mechanisms of membrane traffic to and through the Golgi apparatus have been predicated in large measure on the use of permeabilized animal cells, and on completely cell-free systems. These systems have included those addressing inter-Golgi apparatus membrane traffic, endoplasmic reticulum to Golgi apparatus traffic, and endocytotic events. Development of cell-free systems depends on the use of isolated fractions. Specificity is often achieved by using a compartment-specific assay so that the fractions employed can be very crude. More recently cell-free systems also have evolved which employ highly purified and well-characterized cell fractions. The latter may be utilized in the absence of a compartment-specific assay but may require employment of compartment-specific assays for validation. Central to development of cell-free systems for membrane analysis has been the availability of isolated Golgi apparatus, first from plants and later from animal tissues and cells. A major advantage of cell-free systems is that they are most clearly amenable to the investigation of molecular mechanisms of membrane trafficking.Dedicated to Hilton H. Mollenhauer on the occasion of his retirement     

Ultrastructural changes in the Golgi apparatus and secretory granules of HL-60 cells treated with the imino sugar N-butyldeoxynojirimycin

The imino sugar N-butyldeoxynojirimycin inhibits the N-linked oligosaccharide processing enzymes α-glucosidases I and II, and the ceramide specific glucosyltransferase which catalyses the first step in glucosphingolipid biosynthesis. We have studied the effects of this compound on the ultrastructure of HL-60 cells to identify novel activities of this compound. Treatment of HL-60 cells with this imino sugar results in several morphological changes within the cell, none of which result in cytotoxicity. The plasma membrane stains heavily with potassium ferrocyanide within 30 min following addition of the compound to the medium, and there is then a time dependent involvement of all other intracellular membranes. Secretory granules become enlarged and lose their dense core morphology and appear either empty and vacuolated or have low density contents. However, the most striking effect of NB-DNJ treatment is on the Golgi apparatus. The Golgi exhibits a time-dependent change from typical Golgi morphology to a structure almost completely devoid of cisternae and consisting predominantly of vesicles. All the observed changes are fully reversible on withdrawal of the compound.