Fenestrated cisternae in the Golgi apparatus of the epididymis

Mechanical model of Golgi apparatus

The Golgi apparatus has intrigued researchers since its discovery and despite the advances, there are still many open questions in regards to its shape and function. We propose a mechanical model of Golgi apparatus stack and explain its most elementary geometrical properties: the equilibrium number of cisternae, the stack size, and its general equilibrium shape. Combining both analytical and numerical methods we successfully reconstruct the stack morphology within the theory of bending elasticity. We demonstrate that energy-wise the stack prefers an overall bent shape and show strong evidence that the adhesion strength determines the equilibrium number of cisternae per stack. We explore the morphological role of fenestrations and discuss their impact on the overall stack structure. We also comment on the effects of the asymmetry in the composition of membrane leaflets on the shape of the cisternae and thus offer a broad steady-state study of the stack morphology and present a method that can be used also for other membrane-bound organelles.

Two Golgi integral membrane proteins (GIMPS) exhibit region- and cell type-specific distribution in the epididymis of the adult rat

The epididymis participates in the post-testicular maturation and storage of spermatozoa by secreting proteins into the tubule lumen in a region-specific fashion. The underlying molecular mechanisms leading to biogenesis of these region-specific differences, however, are not known, although components of the Golgi complex membrane container must undoubtedly be intimately involved. Two monoclonal antibodies raised against Golgi integral membrane proteins, recognizing either the cis (GIMPc) or trans Golgi (GIMPt) cisternae, were used as molecular probes of these regions to begin the characterization of the Golgi complex of in vivo and in vitro epididymal cells. Immunolocalization of GIMPs was performed on frozen sections and in cultured cells using biotin-streptavidin-peroxidase immunocytochemistry. In tissue sections, immunostaining of GIMPt was extremely robust in the supranuclear cytoplasm throughout the epididymis. In contrast, no GIMPc immunostaining was detected in the initial segment or in clear cells of the distal caput, corpus, and cauda. Immunodetection of GIMPc and GIMPt in epididymal cells in vitro revealed a reticular, perinuclear pattern, and NH4Cl treatment preferentially disrupted the GIMPt immunolocalization. These results characterizing the molecular components of the Golgi complex will form the basis of additional studies to gain further insight into mechanisms leading to generation of regional differences in epididymal function.

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

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

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

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

A possible new mode of dictyosome duplication in plant cells

Dictyosomes are found in a large number in the glandular scales of Origanum dictamnus during the early developmental stages. Later they significantly diminish when essential oil secretion starts. Phases of dictyosome duplication are frequently observed at the stage of growth of the Golgi apparatus. The process of dictyosome division starts in the middle region of the stack where a Golgi cisterna undergoes a central dilation. An analogous dilation is progressively formed in the adjacent cisternae. Finally, by membrane fusion the stack separates into two daughter stacks which organize into normal dictyosomes.

Three-dimensional ultrastructure of the golgi apparatus in bovine mammary epithelial cells during lactation

The three-dimensional ultrastructure of the Golgi apparatus in milk secreting epithelial cells of bovine mammary gland was explored. From computer-aided reconstructions of serial thin sections, it was determined that the Golgi apparatus was composed of a single set of stacked cisternae. The three-dimensional shape of the dictyosome varied from cell to cell, but the overall shape was that of a hollow cone, cylinder, or bowl. The cis and trans surfaces of the dictyosome were arranged in three-dimensional space such that the cis face was located on the outer surface of the hollow structure and the trans face on the inner surface. The cytoplasmic channel (secretory channel) that traversed the longitudinal axis of the hollow dictyosome contained secretory vesicles. Densely stacked cisternae of rough endoplasmic reticulum surrounded the dictyosome, and microvesicles appeared to fuse with, or bud from, cisternae of both organelles. These findings suggest that Golgi apparatus of the lactating epithelial cell is highly organized and that the Golgi apparatus and secretory channel are essentially an independent compartment within the cell.

Correlative study of the ultrastructure and the physiology of the seasonal regression of the epididymal epithelium in the hedgehog Paraechinus micropus

The seasonal variations in the ultrastructure and physiology of the epididymis of hedgehog were studied in relation to the reproductive functions. Five adult male hedgehogs were sacrificed every alternate month for one calendar year and the epididymis was fixed in Bouin's, Zenker and formol-calcium for light microscopy and in cold buffered glutaraldehyde, post-fixed in osmium tetraoxide for electron microscopy. The epididymal epithelium consists of four types of cells, the principal, the apical, the dark and the basal cells. The principal cells like other steroid synthesizing cells, contain the extensive Golgi apparatus, the smooth and the rough endoplasmic reticulum (SER and RER), the secretory vesicles and the lipid granules during the breeding season, but they are practically devoid of these cell organelles during regression, except for the retarded Golgi and moderate RER. The basal cell, on the other hand, show lipids and well developed organelles during regression but poorly developed structure in the sexually active hedgehog and possibly function as the cells storing lipids during regression and which are subsequently used at the beginning of the recrudescence. The epididymal epithelium recrudesces along with the seminiferous epithelium prior to the spermatozoa reaching the epididymal lumen, whereas the accessory sex glands which are also the extratesticular androgen dependent organs, still show regressed structure. Thus, the ultrastructural and the physiological observations suggest that the principal cells are probably the site of androgen synthesis and they become fully developed along with the cells in the testis on stimulation from the pituitary at the beginning of the recrudescence.

Three-dimensional architecture of the golgi apparatus in Sertoli cells of the rat

Glutaraldehyde-fixed testes were stained "en bloc" with the Ur-Pb-Cu technique of Thiéry and Rambourg ('76) or post-fixed and stained with the osmium tetroxide-potassium ferrocyanide method of Karnovsky ('71). Thin or thick (up to 3 micron) sections were examined with the Philips (301 or 400) EM or the high voltage EM. Stereopairs were prepared with photographs of tilted specimens (+/- 7 degrees). At low magnification, in thick sections (0.5-3 micron) stained with Ur-Pb-Cu, the whole Golgi apparatus formed a single network of interconnected wavy ribbon or platelike structures extending from the juxtanuclear region toward the apex of the cell. At higher magnifications, with the two staining techniques, this Golgi network showed two distinct types of regions: the "saccular region" corresponding to the conventional stack of saccules and the "intersaccular connecting region" made up of anastomotic tubules which bridge adjacent stacks. In the saccurlar regions, there was, on the cis-face of the stack, a tight polygonal meshwork of anastomotic tubules (osmiophilic element). Underlying it there were three to seven closely apposed saccules perforated with pores of various diameters, and finally, on the trans-face, a network of tubules was usually connected to the last saccule of the stack, which seemed to peel off" from the pile. The intersaccular connecting regions showed proximal and distal zones with regard to the associated stacks. The proximal zone was made up of superimposed and parallel polygonal networks of membranous tubules which were continuous with corresponding saccules of the stack. In the distal zone they interdigitated, intertwined, anastomosed and bridged adjacent saccular regions; others turned at right angles and established connections with tubular extensions arising at various levels of the same stack. While cisternae of endoplasmic reticulum were contiguous with tubules or saccules located on the transface of the Golgi apparatus, a close association between the ER cisternae and the cis-face of the stacks was not usually observed.

Studies of the secretory process in the mammalian exocrine pancreas. I. The condensing vacuoles

Phosphatase cytochemistry was used to distinguish between the Golgi apparatus and GERL (considered as a specialized region of endoplasmic reticulum [ER] at the inner [trans] aspect of the Golgi stack) in pancreatic exocrine cells of guinea pig, rat, rabbit, and hamster. The trans element of the Golgi stack exhibits thiamine pyrophosphatase (TPPase) but no acid phosphatase (AcPase) activity. In contrast, GERL shows AcPase but no TPPase activity. The nascent secretory granules, or condensing vacuoles, are expanded cisternal portions of GERL. Continuities of condensing vacuoles with rough ER are suggested, and it is proposed that some secretory components may have direct access to the condensing vacuoles from ER. Connections of Golgi apparatus with GERL were not seen.

Studies on secretory glycoproteins in the rat exocrine pancreas. I. Fine structure of the Golgi complex and release of fucose-labeled proteins after in vivo stimulation with caerulein

Using a double-label technique on isolated rat pancreatic lobules, the rate of synthesis and discharge of regular and fucosylated secretory proteins was studied under control conditions and after in vivo prestimulation with caerulein. Both labeled leucine and fucose were incorporated into pancreatic proteins at a linear rate, which was potentiated by in vivo stimulation. In pulse-chase experiments both regular and fucosylated secretory proteins were discharged into the medium in parallel. The in vivo pretreatment with caerulein caused an earlier discharge and increased the total amount released. Kinetic analysis of unstimulated (baseline) discharge of both classes of secretory proteins indicated in vitro sensitivity by the previous in vivo treatment with caerulein. The biochemical data were compared to the fine structure of the Golgi complex under both control and prestimulated ocnditions. The Golgi stacks were composed of four to six individual cisternae which in some cases were connected by intercisternal pores. Transporting vesicles were observed fusing along the total length of the outermost cisterna on both the cis- and trans-side and with the lateral ends of the intermediate cisternae. Under control conditions only the last trans-cisterna contained some electron opaque material; in vivo prestimulation led to distension and filling of all disternae in an individual Golgi-unit. Numerous stages of transformation of the last transcisterna into condensing vacuoles were observed, lending support to the hypothesis that during packaging of secretory products the membranes of the Golgi complex undergo a continuous turnover.

Fenestrae in golgi and endoplasmic reticulum cisternae of human brain tumours

Fenestrae were found in freeze-fractured cisternae of the Golgi apparatus and endoplasmic reticulum of glioblastoma, oligodendroglioma, ependymoma, medulloblastoma, medulloepithelioma, meningioma, cerebellar sarcoma, hemangioblastoma, and chromophobe adenoma. They were about 200--400 A in diameter and often diffusely distributed or concentrated in groups in Golgi cisternae, while they were around 300--600 A in size and scattered in distribution in cisternae of endoplasmic reticulum. They appeared as conical protrusions or circular broken-off necks of face A and as circular holes on face B in tangential fractures, and as several constrictions of cisternae in cross fractures.

Effects of phosphotungstate negative staining on the morphology of the isolated Golgi apparatus

Isolated Golgi complexes can be recognized in phosphotungstate (PTA) negative stain as stacks of membranous plates surrounded by a complex anastomosing network of tubules and vesicles. The extent of this tubular network is, however, much greater than can be observed in thin sections of whole cells. To determine which of the steps leading to the final negatively stained image may produce the observed changes, we have monitored each of the steps by other electron microscope and biochemical methods. The first damage to the membranes seems to occur during the initial isolation procedure as judged by the appearance of smooth patches on the freeze-fractured membrane faces that are normally covered with particles. Subsequent suspension of the Golgi fraction in water, to dilute the sucrose for negative staining, leads to the disappearnce of the stacking, to some tubulation and some vesiculation of the membranes as judged by thin section and freeze-cleave microscopy. The latter technique also reveals an increase in smooth-cleaving membrane faces. Application of the negative stain to the water-washed Golgi fraction, finally, produces extensive tubular arrays and a simultaneous decrease in the remaining large membranous vesicles. The freeze-cleaved tubular membranes appear essentially smooth except for small patches of aggregated particles. Parallel gel electrophoresis studies of the membranes and of the water and negative stain wash extracts indicate that protein extraction is involved in these morphological changes. PTA seems to be a particularly effective solvent for certain membrane proteins that are not removed by the water wash. These observations suggest that removal of membrane proteins alters structural restraints on the membrane lipids so that they behave semiautonomously like myelinics and form new artificial structures. This does not eliminate the possibility, however, that some tubules also exist in the Golgi apparatus in vivo.

Golgi apparatus, GERL, and lysosomes of neurons in rat dorsal root ganglia, studied by thick section and thin section cytochemistry

New insights into the ultrastructure and phosphatase localizations of Golgi apparatus and GERL, and into the probable origin of lysosomes in the neurons of fetal dorsal root ganglia and the small neurons of adult ganglia have come from studying thick (0.5-1.0 micro) as well as thin (up to 500 A) sections by conventional electron microscopy. Tilting the thick specimens, by a goniometer stage, has helped to increase our understanding of the three-dimensional aspects of the Golgi apparatus and GERL. One Golgi element, situated at the inner aspect of the Golgi stack, displays thiamine pyrophosphatase and nucleoside diphosphatase activities. This element exhibits regular geometric arrays (hexagons) of interconnected tubules without evidence of a flattened portion (saccule or cisterna). In contrast, GERL shows acid phosphatase activity and possesses small cisternal portions and anastomosing tubules. Lysosomes appear to bud from GERL. Osmium deposits, following prolonged osmication, are found in the outer Golgi element. Serial 0.5-micro and thin sections of thiamine pyrophosphatase-incubated material demonstrate that, in the neurons studied, the Golgi apparatus is a continuous network coursing through the cytoplasm. Serial thick sections of acid phosphatase-incubated tissue suggest that GERL is also a continuous structure throughout the cytoplasm. Tubules of smooth endoplasmic reticulum, possibly part of GERL, extend into the polygonal compartments of the inner Golgi element. The possible physiological significance of a polygonal arrangement of a phosphatase-rich Golgi element in proximity to smooth ER is considered. A tentative diagram of the Golgi stack and associated endoplasmic reticulum in these neurons has been drawn.

Growth and differentiation of cytoplasmic membranes in the course of lipoprotein granule synthesis in the hepatic cell. I. Elaboration of elements of the Golgi complex

The synthesis of "very low" density lipoprotein in liver cells is characterized by the fact that the synthesized products, mostly triglycerides, are processed in the form of discrete, size-limited granules or globules, about 400 A in diameter. The present investigation has been made possible in part by the use of a fixative (OsO(4) in bidistilled H(2)O at pH 6.0, in the absence of electrolytes) particularly effective in preserving cytoplasmic membranes and lipids, and giving them high stainability and differential contrast. Under these technical conditions, the lipoprotein granules retain their morphology and high density to electrons practically unaltered, and may serve as tracers in determining their route of transport from the sites of synthesis, starting at the rough-smooth ER junctions, to the lumen of Golgi concentrating vesicles. From the observations, it may be deduced that, along with lipoprotein granule synthesis and transport, there are also production and transfer of new membranes in the form of tubular extensions of smooth ER network which, by progressive fusion and coalescence, participate in the elaboration of fenestrated plates and solid Golgi sacs. In contradistinction to the entire process of liver lipoprotein granule synthesis, transport, and segregation, as reported in the present paper, appears to constitute a developmental sequence which includes the following communicating compartments, in consecutive order: cisternae of rough ER where proteins and possibly phospholipids are synthesized, smooth ER network where triglycerides are synthesized and transported in the form of dense granules, fusion of smooth ER tubular extensions into Golgi fenestrated plates, and further coalescence into solid Golgi sacs, ending in the segregation of the granules in appended concentrating vesicles, or detached "secretory vesicles." It seems that it is this progressive evolution in growth and configuration of membranes which is reflected in the so called polarity, from forming to mature faces, of the Golgi apparatus.