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PubMed1982

Polarization of the Golgi apparatus and the microtubule-organizing center in cultured fibroblasts at the edge of an experimental wound.

We have used the technique of experimental wounding of confluent monolayers of normal fibroblasts to induce essentially unidirectional and synchronous cell movement at the edge of the wound. The intracellular location of the Golgi apparatus and the microtubule-organizing center was determined by double indirect immunofluorescence microscopy, using antibodies specific for the membranes of the Golgi apparatus and antibodies specific for tubulin, respectively. In cells at the wound edge, the immunolabeled Golgi apparatus and microtubule-organizing center were in close proximity to one another and located predominantly forward of the cell nucleus facing the wound. In the same cultures in cells removed from the wound, the two organelles were also coordinately located; however, they were randomly oriented with respect to the wound edge. This reorientation of the two organelles in cells at the wound edge was evident within minutes after wounding and persisted as cell extension subsequently occurred into the wound. These results suggest that both the Golgi apparatus and the microtubule-organizing center may participate in directing cell movement. The possible mechanisms involved are discussed in the light of previous hypotheses and experimental evidence concerning cell motility.

Animals↗
PubMed1993

Fragmentation and dispersal of Golgi proteins and redistribution of glycoproteins and glycolipids processed through the Golgi apparatus after infection with herpes simplex virus 1.

In Vero monkey cells and HEp-2 human epidermoid carcinoma cells infected with herpes simplex virus 1 the proteins beta-COP, galactosyltransferase, and alpha-mannosidase II associated with the Golgi apparatus appear to be associated with numerous smaller structures dispersed throughout the cytoplasm. Concomitantly, the intracytoplasmic ligands of lectins normally associated wholly (Helix pomatia or Ricinus communis agglutinin) or in part (wheat germ agglutinin) with the Golgi apparatus increased in amount and became dispersed. This phenomenon was seen in some of the baby hamster kidney cells analyzed but not in others and not in the human 143TK- cells. The fragmentation and dispersal of the Golgi apparatus was a late event in the reproductive cycle coinciding with virion assembly, processing of viral glycoproteins, and exocytosis from infected cells. The fragmentation of the Golgi apparatus is morphologically different from that seen with brefeldin A and may reflect disequilibration between the anterograde and retrograde Golgi transport caused by the huge influx of viral glycoproteins contained in virions and membranes flowing through the exocytic pathway.

Animals↗
PubMed1996

SNAP prevents Mg(2+)-ATP-induced release of N-ethylmaleimide-sensitive factor from the Golgi apparatus in digitonin-permeabilized PC12 cells.

The N-ethylmaleimide-sensitive factor (NSF), which is involved in the multisteps of protein transport, is released from Golgi membranes on in vitro incubation with Mg(2+)-ATP. However, several lines of evidence suggest that NSF is associated with membranes in spite of the presence of Mg2+ and ATP in vivo. We have used digitonin-permeabilized PC12 cells to investigate the mechanism underlying the association of NSF with membranes. In PC12 cells, immunoreactivity for NSF was observed in the nuclear membranes, the Golgi apparatus, and neuronal growth cones, where synaptic vesicles are concentrated. NSF associated with the Golgi apparatus was released on incubation with Mg(2+)-ATP, whereas NSF in the nuclear membranes and neuronal growth cones was not released on the same treatment. The addition of cytosol blocked the Mg(2+)-ATP-induced release of NSF from the Golgi apparatus. Chromatographic analyses revealed that the factor(s) that prevents NSF release from the Golgi apparatus was eluted at the same position as the soluble NSF attachment proteins (SNAPs). Purified His6-tagged alpha-SNAP exhibited such activity. His6-tagged alpha-SNAP also prevented the Mg(2+)-ATP-induced release of NSF from isolated Golgi membranes.

Adenosine Triphosphate↗
PubMed2002

AKAP350 at the Golgi apparatus. II. Association of AKAP350 with a novel chloride intracellular channel (CLIC) family member.

AKAP350 can scaffold a number of protein kinases and phosphatases at the centrosome and the Golgi apparatus. We performed a yeast two-hybrid screen of a rabbit parietal cell library with a 3.2-kb segment of AKAP350 (nucleotides 3611-6813). This screen yielded a full-length clone of rabbit chloride intracellular channel 1 (CLIC1). CLIC1 belongs to a family of proteins, all of which contain a high degree of homology in their carboxyl termini. All CLIC family members were able to bind a 133-amino acid domain within AKAP350 through the last 120 amino acids in the conserved CLIC carboxyl termini. Antibodies developed against a bovine CLIC, p64, immunoprecipitated AKAP350 from HCA-7 colonic adenocarcinoma cell extracts. Antibodies against CLIC proteins recognized at least five CLIC species including a novel 46-kDa CLIC protein. We isolated the human homologue of bovine p64, CLIC5B, from HCA-7 cell cDNA. A splice variant of CLIC5, the predicted molecular mass of CLIC5B corresponds to the molecular mass of the 46-kDa CLIC immunoreactive protein in HCA-7 cells. Antibodies against CLIC5B colocalized with AKAP350 at the Golgi apparatus with minor staining of the centrosomes. AKAP350 and CLIC5B association with Golgi elements was lost following brefeldin A treatment. Furthermore, GFP-CLIC5B-(178-410) targeted to the Golgi apparatus in HCA-7 cells. The results suggest that AKAP350 associates with CLIC proteins and specifically that CLIC5B interacts with AKAP350 at the Golgi apparatus in HCA-7 cells.

A Kinase Anchor Proteins↗
PubMed2002

Transforming acidic coiled-coil-containing protein 4 interacts with centrosomal AKAP350 and the mitotic spindle apparatus.

AKAP350 is a multiply spliced family of 350-450-kDa protein kinase A-anchoring proteins localized to the centrosomes and the Golgi apparatus. Using AKAP350A as bait in a yeast two-hybrid screen of a rabbit parietal cell library, we have identified a novel AKAP350-interacting protein, transforming acidic coiled-coil-containing protein 4 (TACC4). Two-hybrid binary assays demonstrate interaction of both TACC3 and TACC4 with AKAP350A and AKAP350B. Antibodies raised to a TACC4-specific peptide sequence colocalize TACC4 with AKAP350 at the centrosome in interphase Jurkat cells. Mitotic cell staining reveals translocation of TACC4 from the centrosome to the spindle apparatus with the majority of TACC4 at the spindle poles. Truncated TACC4 proteins lacking the AKAP350 minimal binding domain found in the carboxyl coiled-coil region of TACC4 could no longer target to the centrosome. Amino-truncated TACC4 proteins could no longer target to the spindle apparatus. Further, overexpression of TACC4 fusion proteins that retained spindle localization in mitotic cells resulted in an increased proportion of cells present in prometaphase. We propose that AKAP350 is responsible for sequestration of TACC4 to the centrosome in interphase, whereas a separate TACC4 domain results in functional localization of TACC4 to the spindle apparatus in mitotic cells.

A Kinase Anchor Proteins↗
PubMedDate not supplied

Golgi apparatus partitioning during cell division.

This review discusses the mitotic segregation of the Golgi apparatus. The results from classical biochemical and morphological studies have suggested that in mammalian cells this organelle remains distinct during mitosis, although highly fragmented through the formation of mitotic Golgi clusters of small tubules and vesicles. Shedding of free Golgi-derived vesicles would consume Golgi clusters and disperse this organelle throughout the cytoplasm. Vesicles could be partitioned in a stochastic and passive way between the two daughter cells and act as a template for the reassembly of this key organelle. This model has recently been modified by results obtained using GFP- or HRP-tagged Golgi resident enzymes, live cell imaging and electron microscopy. Results obtained with these techniques show that the mitotic Golgi clusters are stable entities throughout mitosis that partition in a microtubule spindle-dependent fashion. Furthermore, a newer model proposes that at the onset of mitosis, the Golgi apparatus completely loses its identity and is reabsorbed into the endoplasmic reticulum. This suggests that the partitioning of the Golgi apparatus is entirely dependent on the partitioning of the endoplasmic reticulum. We critically discuss both models and summarize what is known about the molecular mechanisms underlying the Golgi disassembly and reassembly during and after mitosis. We will also review how the study of the Golgi apparatus during mitosis in other organisms can answer current questions and perhaps reveal novel mechanisms.

Animals↗
PubMed1985

Is cytochrome P-450 transported from the endoplasmic reticulum to the Golgi apparatus in rat hepatocytes?

The Golgi apparatus mediates intracellular transport of not only secretory and lysosomal proteins but also membrane proteins. As a typical marker membrane protein for endoplasmic reticulum (ER) of rat hepatocytes, we have selected phenobarbital (PB)-inducible cytochrome P-450 (P-450[PB]) and investigated whether P-450(PB) is transported to the Golgi apparatus or not by combining biochemical and quantitative ferritin immunoelectron microscopic techniques. We found that P-450(PB) was not detectable on the membrane of Golgi cisternae either when P-450 was maximally induced by phenobarbital treatment or when P-450 content in the microsomes rapidly decreased after cessation of the treatment. The P-450 detected biochemically in the Golgi subcellular fraction can be explained by the contamination of the microsomal vesicles derived from fragmented ER membranes to the Golgi fraction. We conclude that when the transfer vesicles are formed by budding on the transitional elements of ER, P-450 is completely excluded from such regions and is not transported to the Golgi apparatus, and only the membrane proteins destined for the Golgi apparatus, plasma membranes, or lysosomes are selectively collected and transported.

Animals↗
PubMed1991

Transport of exogenous fluorescent phosphatidylserine analogue to the Golgi apparatus in cultured fibroblasts.

We have examined intracellular transport and metabolism of the fluorescent analogue of phosphatidylserine, 1-palmitoyl-2-(N-[12[(7-nitrobenz-2-oxa-1,3-diazole-4-yl)amino] dodecanoyl])-phosphatidylserine ([palmitoyl-C12-NBD]-PS) in cultured fibroblasts. When monolayer cultures were incubated with liposomes containing (palmitoyl-C12-NBD)-PS at 37 degrees C, fluorescent PS was transported to the Golgi apparatus. NBD-containing analogues of phosphatidylcholine, phosphatidylethanolamine (PE), or phosphatidic acid did not accumulate in the Golgi apparatus under the same experimental conditions. We suggest that the transport is not due to endocytosis, but is the result of incorporation and trans-bilayer movement of the (palmitoyl-C12-NBD)-PS at the plasma membrane followed by translocation of the lipid from plasma membrane to the Golgi apparatus via nonvesicular mechanisms. Uptake of fluorescent PS was inhibited by depletion of cellular ATP and was blocked by structural analogues of the lipid or by pretreatment of cells with glutaraldehyde or N-ethylmaleimide. After incorporation into the cell, fluorescent PS was metabolized to fluorescent PE. The intracellular distribution of fluorescence changed during the conversion. In addition to the Golgi apparatus, mitochondria also became labeled.

Animals↗
PubMed1992

A 62-kD protein required for mitotic progression is associated with the mitotic apparatus during M-phase and with the nucleus during interphase.

A protein of 62 kD is a substrate of a calcium/calmodulin-dependent protein kinase, and both proteins copurify with isolated mitotic apparatuses (Dinsmore, J. H., and R. D. Sloboda. 1988. Cell. 53:769-780). Phosphorylation of the 62-kD protein increases after fertilization; maximum incorporation of phosphate occurs during late metaphase and anaphase and correlates directly with microtubule disassembly as determined by in vitro experiments with isolated mitotic apparatuses. Because 62-kD protein phosphorylation occurs in a pattern similar to the accumulation of the mitotic cyclin proteins, experiments were performed to determine the relationship between cyclin and the 62-kD protein. Continuous labeling of marine embryos with [35S]methionine, as well as immunoblots of marine embryo proteins using specific antibodies, were used to identify both cyclin and the 62-kD protein. These results clearly demonstrate that the 62-kD protein is distinct from cyclin and, unlike cyclin, is a constant member of the cellular protein pool during the first two cell cycles in sea urchin and surf clam embryos. Similar results were obtained using immunofluorescence microscopy of intact eggs and embryos. In addition, immunogold electron microscopy reveals that the 62-kD protein associates with the microtubules of the mitotic apparatus in dividing cells. Interestingly, the protein changes its subcellular distribution with respect to microtubules during the cell cycle. Specifically, during mitosis the 62-kD protein associates with the mitotic apparatus; before nuclear envelope breakdown, however, the 62-kD protein is confined to the nucleus. After anaphase, the 62-kD protein returns to the nucleus, where it resides until nuclear envelope disassembly of the next cell cycle.

Animals↗
PubMed1994

Internalization and sorting of a fluorescent analogue of glucosylceramide to the Golgi apparatus of human skin fibroblasts: utilization of endocytic and nonendocytic transport mechanisms.

We examined the uptake and intracellular transport of the fluorescent glucosylceramide analogue N-[5-(5,7-dimethyl BODIPYTM)-1-pentanoyl]-glucosyl sphingosine (C5-DMB-GlcCer) in human skin fibroblasts, and we compared its behavior to that of the corresponding fluorescent analogues of sphingomyelin, galactosylceramide, and lactosylceramide. All four fluorescent analogues were readily transferred from defatted BSA to the plasma membrane during incubation at 4 degrees C. When cells treated with C5-DMB-GlcCer were washed, warmed to 37 degrees C, and subsequently incubated with defatted BSA to remove fluorescent lipid at the cell surface, strong fluorescence was observed at the Golgi apparatus, as well as weaker labeling at the nuclear envelope and other intracellular membranes. Similar results were obtained with C5-DMB-galactosylceramide, except that labeling of the Golgi apparatus was weaker than with C5-DMB-GlcCer. Internalization of C5-DMB-GlcCer was not inhibited by various treatments, including ATP depletion or warming to 19 degrees C, and biochemical analysis demonstrated that the lipid was not metabolized during its internalization. However, accumulation of C5-DMB-GlcCer at the Golgi apparatus was reduced when cells were treated with a nonfluorescent analogue of glucosylceramide, suggesting that accumulation of C5-DMB-GlcCer at the Golgi apparatus was a saturable process. In contrast, cells treated with C5-DMB-analogues of sphingomyelin or lactosylceramide internalized the fluorescent lipid into a punctate pattern of fluorescence during warming at 37 degrees C, and this process was temperature and energy dependent. These results with C5-DMB-sphingomyelin and C5-DMB-lactosylceramide were analogous to those obtained with another fluorescent analogue of sphingomyelin in which labeling of endocytic vesicles and plasma membrane lipid recycling were documented (Koval, M., and R. E. Pagano. 1990. J. Cell Biol. 111:429-442). Incubation of perforated cells with C5-DMB-sphingomyelin resulted in prominent labeling of the nuclear envelope and other intracellular membranes, similar to the pattern observed with C5-DMB-GlcCer in intact cells. These observations are consistent with the transbilayer movement of fluorescent analogues of glucosylceramide and galactosylceramide at the plasma membrane and early endosomes of human skin fibroblasts, and suggest that both endocytic and nonendocytic pathways are used in the internalization of these lipids from the plasma membrane.

Adenosine Triphosphate↗
PubMed1998

Direct pathway from early/recycling endosomes to the Golgi apparatus revealed through the study of shiga toxin B-fragment transport.

Shiga toxin and other toxins of this family can escape the endocytic pathway and reach the Golgi apparatus. To synchronize endosome to Golgi transport, Shiga toxin B-fragment was internalized into HeLa cells at low temperatures. Under these conditions, the protein partitioned away from markers destined for the late endocytic pathway and colocalized extensively with cointernalized transferrin. Upon subsequent incubation at 37 degreesC, ultrastructural studies on cryosections failed to detect B-fragment-specific label in multivesicular or multilamellar late endosomes, suggesting that the protein bypassed the late endocytic pathway on its way to the Golgi apparatus. This hypothesis was further supported by the rapid kinetics of B-fragment transport, as determined by quantitative confocal microscopy on living cells and by B-fragment sulfation analysis, and by the observation that actin- depolymerizing and pH-neutralizing drugs that modulate vesicular transport in the late endocytic pathway had no effect on B-fragment accumulation in the Golgi apparatus. B-fragment sorting at the level of early/recycling endosomes seemed to involve vesicular coats, since brefeldin A treatment led to B-fragment accumulation in transferrin receptor-containing membrane tubules, and since B-fragment colocalized with adaptor protein type 1 clathrin coat components on early/recycling endosomes. Thus, we hypothesize that Shiga toxin B-fragment is transported directly from early/recycling endosomes to the Golgi apparatus. This pathway may also be used by cellular proteins, as deduced from our finding that TGN38 colocalized with the B-fragment on its transport from the plasma membrane to the TGN.

Adaptor Protein Complex gamma Subunits↗
PubMed1999

Genetic evidence for ATP-dependent endoplasmic reticulum-to-Golgi apparatus trafficking of ceramide for sphingomyelin synthesis in Chinese hamster ovary cells.

LY-A strain is a Chinese hamster ovary cell mutant resistant to sphingomyelin (SM)-directed cytolysin and has a defect in de novo SM synthesis. Metabolic labeling experiments with radioactive serine, sphingosine, and choline showed that LY-A cells were defective in synthesis of SM from these precursors, but not syntheses of ceramide (Cer), glycosphingolipids, or phosphatidylcholine, indicating a specific defect in the conversion of Cer to SM in LY-A cells. In vitro experiments showed that the specific defect of SM formation in LY-A cells was not due to alterations in enzymatic activities responsible for SM synthesis or degradation. When cells were treated with brefeldin A, which causes fusion of the Golgi apparatus with the endoplasmic reticulum (ER), de novo SM synthesis in LY-A cells was restored to the wild-type level. Pulse-chase experiments with a fluorescent Cer analogue, N-(4,4-difluoro-5,7-dimethyl-4-bora-3a, 4a-diaza-s-indacene-3-pentanoyl)-D-erythro-sphingosine (C5-DMB-Cer), revealed that in wild-type cells C5-DMB-Cer was redistributed from intracellular membranes to the Golgi apparatus in an intracellular ATP-dependent manner, and that LY-A cells were defective in the energy-dependent redistribution of C5-DMB-Cer. Under ATP-depleted conditions, conversion of C5-DMB-Cer to C5-DMB-SM and of [3H]sphingosine to [3H]SM in wild-type cells decreased to the levels in LY-A cells, which were not affected by ATP depletion. ER-to-Golgi apparatus trafficking of glycosylphosphatidylinositol-anchored or membrane-spanning proteins in LY-A cells appeared to be normal. These results indicate that the predominant pathway of ER-to-Golgi apparatus trafficking of Cer for de novo SM synthesis is ATP dependent and that this pathway is almost completely impaired in LY-A cells. In addition, the specific defect of SM synthesis in LY-A cells suggests different pathways of Cer transport for glycosphingolipids versus SM synthesis.

Adenosine Triphosphate↗
PubMed1962

The mitotic apparatus. Fine structure of the isolated unit.

The fine structure of the mitotic apparatus isolated from the sea urchin egg has been investigated. The isolation was accomplished by lysis of metaphase eggs in a 1 M solution of hexanediol, buffered at pH 6. The fine structure of the isolated apparatus was studied after fixation with osmium tetroxide directly in the isolation medium. The spindle is composed of fine fibrils, approximately 20 mmicro in diameter, which appear tubular. Similar fibrils, radially oriented, are found in the aster. If the isolated mitotic apparatus is exposed to water at pH 6 before fixation, the structure is considerably modified. The most pronounced effects are an increase in the number of large membrane-bounded vesicles and in the amount of free granular material present. The conditions necessary for the fixation of the mitotic apparatus in dividing cells are discussed in the light of these observations on the isolated unit.

Animals↗
PubMed2001

The localization of human cyclins B1 and B2 determines CDK1 substrate specificity and neither enzyme requires MEK to disassemble the Golgi apparatus.

In this paper, we show that substrate specificity is primarily conferred on human mitotic cyclin-dependent kinases (CDKs) by their subcellular localization. The difference in localization of the B-type cyclin-CDKs underlies the ability of cyclin B1-CDK1 to cause chromosome condensation, reorganization of the microtubules, and disassembly of the nuclear lamina and of the Golgi apparatus, while it restricts cyclin B2-CDK1 to disassembly of the Golgi apparatus. We identify the region of cyclin B2 responsible for its localization and show that this will direct cyclin B1 to the Golgi apparatus and confer upon it the more limited properties of cyclin B2. Equally, directing cyclin B2 to the cytoplasm with the NH(2) terminus of cyclin B1 confers the broader properties of cyclin B1. Furthermore, we show that the disassembly of the Golgi apparatus initiated by either mitotic cyclin-CDK complex does not require mitogen-activated protein kinase kinase (MEK) activity.

Animals↗
PubMed2001

Evidence that the entire Golgi apparatus cycles in interphase HeLa cells: sensitivity of Golgi matrix proteins to an ER exit block.

We tested whether the entire Golgi apparatus is a dynamic structure in interphase mammalian cells by assessing the response of 12 different Golgi region proteins to an endoplasmic reticulum (ER) exit block. The proteins chosen spanned the Golgi apparatus and included both Golgi glycosyltransferases and putative matrix proteins. Protein exit from ER was blocked either by microinjection of a GTP-restricted Sar1p mutant protein in the presence of a protein synthesis inhibitor, or by plasmid-encoded expression of the same dominant negative Sar1p. All Golgi region proteins examined lost juxtanuclear Golgi apparatus-like distribution as scored by conventional and confocal fluorescence microscopy in response to an ER exit block, albeit with a differential dependence on Sar1p concentration. Redistribution of GalNAcT2 was more sensitive to low Sar1p(dn) concentrations than giantin or GM130. Redistribution was most rapid for p27, COPI, and p115. Giantin, GM130, and GalNAcT2 relocated with approximately equal kinetics. Distinct ER accumulation could be demonstrated for all integral membrane proteins. ER-accumulated Golgi region proteins were functional. Photobleaching experiments indicated that Golgi-to-ER protein cycling occurred in the absence of any ER exit block. We conclude that the entire Golgi apparatus is a dynamic structure and suggest that most, if not all, Golgi region-integral membrane proteins cycle through ER in interphase cells.

Autoantigens↗
PubMed1959

Studies on the mitotic apparatus of the sea urchin by means of antigen-antibody reactions in agar.

The primary purpose of the experiments reported in this paper was to gain information on the molecular origin of the mitotic apparatus. Antisera were prepared against unfertilized sea urchin (Strongylocentrotus purpuratus) egg antigens and mitotic apparatus antigens. These were permitted to react with various antigen solutions in Ouchterlony agar gel diffusion plates, and the resultant precipitation patterns analysed. The results revealed that the mitotic apparatus contains probably no more than two antigens (precursor-1 component and precursor-2 component) and that these are shared by the unfertilized egg. Absorption and fractionation techniques indicated that in the unfertilized egg the precursor-1 component is present both as a "soluble" protein and as an insoluble form tenaciously associated with intracellular structural elements. A survey of dividing and non-dividing tissues for the precursor-1 component revealed that it was restricted to tissues in which mitotic activity could be detected microscopically. No immunochemical relationship could be detected between the mitotic apparatus and proteins extracted, by various methods, from the lantern muscle.

Agar↗
PubMed1978

Passage of serum-destined proteins through the Golgi apparatus of rat liver. An examination of heavy and light Golgi fractions.

The participation of hepatic Golgi apparatus in the intracellular transport of blood-destined proteins has been analyzed using Golgi fractions enriched in cis and trans components of the Golgi apparatus. SDS-polyacrylamide gel electrophoresis of the liver Golgi fractions showed several proteins corresponding in relative proportions and mobilities with serum proteins. After a pulse injection of labeled leucine, the secretory content of the cis Golgi fraction was labeled earlier than the trans Golgi fraction. Taken together, the results show the participation of the liver Golgi apparatus in the secretion of most of the serum proteins and provide documentation for a sequential progression of secretory protein through the cis and trans components of the Golgi apparatus.

Animals↗
PubMed1981

Golgi apparatus, GERL, and secretory granule formation within neurons of the hypothalamo-neurohypophysial system of control and hyperosmotically stressed mice.

The vasopressin-producing neurons of the hypothalamo-neurohypophysial system are a particularly good model with which to consider the relationship between the Golgi apparatus nd GERL and their roles in secretory granule production because these neurons increase their synthesis and secretion of vasopressin in response to hyperosmotic stress. Enzyme cytochemical techniques for acid phosphatase (AcPase) and thiamine pyrophosphatase (TPPase) activities were used to distinguish GERL from the Golgi apparatus in cell bodies of the supraoptic nucleus from normal mice, mice hyperosmotically stressed by drinking 2% salt water, and mice allowed to recover for 5-10 d from hyperosmotic stress. In nonincubated preparations of control supraoptic perikarya, immature secretory granules at the trans face of the Golgi apparatus were frequently attached to a narrow, smooth membrane cisterna identified as GERL. Secretory granules were occasionally seen attached to Golgi saccules. TPPase activity was present in one or two of the trans Golgi saccules; AcPase activity appeared in GERL and attached immature secretory granules, rarely in the trans Golgi saccules, and in secondary lysosomes. As a result of hyperosmotic stress, the Golgi apparatus hypertrophied, and secretory granules formed from all Golgi saccules and GERL. Little or no AcPase activity could be demonstrated in GERL, whereas all Golgi saccules and GERL-like cisternae were TPPase positive. During recovery, AcPase activity in GERL returned to normal; however, the elevated TPPase activity and secretory granule formation seen in GERL-like cisternae and all Golgi saccules during hyperosmotic stress persisted. These results suggest that under normal conditions GERL is the predominant site for the secretory granule formation, but during hyperosmotic stress, the Golgi saccules assume increased importance in this function. The observed cytochemical modulations in Golgi saccules and GERL suggest that GERL is structurally and functionally related to the Golgi saccules.

Acid Phosphatase↗