A fine-structural analysis of mouse molar odontoblast maturation.

The first mandibular molars of the Swiss albino mice, 1 through 4 days of age, were fixed in glutaraldehyde or Karnovsky's fixative. The tissues were postfixed in OSO4, dehydrated and embedded in Epon. The prepolarizing, polarizing and secretory odontoblasts were described. The prepolarizing cells, located in the vicinity of the cervical loop, were mesenchymal-like in morphology. The cells of the polarizing stage possessed organelles indicative of protein synthesis. The nucleus was located proximally. Aperiodic fibers were evident in the wide basement membrane. The secretory odontoblasts were long, slender, polarized cells closely adjoining one another. Each odontoblast possessed six morphologically discernible regions: (1) an infranuclear region, limited in size and containing few cellular organelles; (2) a nuclear region, housing the oval nucleus and a few associated lamellae of rough endoplasmic reticulum as well as a limited number of mitochondria; (3) a supranuclear rough endoplasmic reticulum region, possessing an abundance of these organelles as well as some mitochondria and secretory vesicles; (4) a Golgi region, occupying the middle third of the cell, housing the elements of an extensive Golgi apparatus which was surrounded by peripherally located profiles of rough endoplasmic reticulum; additionally, this region contained smooth endoplasmic reticulum, mitochondria, numerous secretory granules and vesicles and occasional intracellular collagen fibers; (5) an apical rough endoplasmic reticulum region, containing a rough endoplasmic reticulum component that was less extensive than its supranuclear counterpart; in addition, this region was the one richest in mitochondria and contained a plethora of secretory vesicles and granules; (6) the odontoblastic process, a region mostly void of organelles, containing various secretory products, some of which appeared to be in the process of being released extracellularly into the surrounding dentin matrix.     

Isolation of a Golgi rich fraction from rat ventral prostate

Unmodified procedures for isolation of fractions rich in Golgi elements from other tissues have not proved applicable to the rat ventral prostate because of the tendency of membranous material to aggregate. We have devised a new procedure whereby: 1) a Golgi rich fraction from rat ventral prostate was released by a gentle two-step homogenization and isolated by centrifugation through discontinuous sucrose density gradients; 2) the specific activity of UDP-galactose: glycoprotein galactosyltransferase increased 69-fold in this fraction; 3) the isolated Golgi fraction was reasonably free from mitochondria, lysosomes, endoplasmic reticulum and plasma membranes as shown by the relatively low activities of marker enzymes; 4) the specific activities of acid phosphatase and 5'-nucleotidase in the Golgi rich fraction was 4 times greater than that in prostate homogenate. Both enzymes are secretory products and their presence in Golgi elements is probably associated with their packaging in secretory granules.     

Giant mitochondria distinct from enlarged mitochondria in secretory and ciliated cells of gerbil trachea and bronchioles

Numerous mitochondria ranging from slightly larger than normal to several micrometers in diameter (giant) were found in about one-half the serous secretory cells in the surface epithelium of the normal gerbil trachea and proximal bronchi. Tracheal serous cells of mice also were found to contain numerous giant mitochondria. Clara cells of gerbil bronchioles contained abundant giant mitochondria in addition to normal tubular mitochondria and the second population of enlarged spherical mitochondria that have been described in Clara cells of several genera. In contrast, mouse Clara cells revealed the normal tubular and the enlarged spherical mitochondria but no giant mitochondria. A survey of a number of cell types in gerbils failed to disclose hypertrophied mitochondria outside tracheobronchial surface epithelium and bronchioles. The mitochondrial enlargement resulted from an increase of matrix but not cristae. The expansion of matrix displaced the relatively sparse cristae into small collections compressed against the outer membrane. The prevalence of giant mitochondria and of granular endoplasmic reticulum is similar among cells, and these two organelles are codistributed within cells. The megamitochondria and granular reticulum occupy a central stratum, whereas normal mitochondria occur in the apical and basal regions. The giant mitochondria are considered related to a normal biologic activity that is characteristic of respiratory tract epithelium of mice and gerbils selectively and is more prominent in secretory cells than in ciliated cells.     

Ultrastructure of the sexual segments of the kidney in male and female lizards,Cnemidophorus l. lemniscatus (L.)

Summary Kidneys of adult male and female lizards were studied by electron microscopy, in order to understand the ultrastructure of the collecting duct and a differentiated part thereof, the sexual segment, which is an important accessory sexual organ. First portion of sexual segment in males: The cells are filled with large secretory granules of a wide range of opacities. The granular endoplasmic reticulum is abundant; basal formations of superimposed flat cisternae are frequent. Distended vesicles and microvesicles prevail in the supranuclear, well developed Golgi apparatus. Evidences indicate that secretion of these cells is holocrine. Second portion of sexual segment in males: All of the secretory granules are apical in location and relatively electron-opaque; they show a denser core. This core is formed by a substance which, after lying in contact with ribosomes, enters the secretory vesicles of the highly developed Golgi apparatus. A lighter substance is then condensed around it. The secretion of the granules is merocrine. The granular endoplasmic reticulum is very abundant in these cells, but basal ergastoplasmic formations are lacking. Sexual segment in females: The cells show features similar to those of the male first portion, but they are smaller. Undifferentiated collecting duct: Most of the cells are mucigenic. They have small ovoid, apical secretory granules. The density of the granules varies from cell to cell; when they are electron-lucent, they exhibit laminar or dotted opaque figures. Moderately developed Golgi apparatus and granular endoplasmic reticulum, as well as elongated mitochondria, occur in mucigenic cells. Intercalated among the latter are non-secretory cells. They have very abundant mitochondria, numerous microvilli, many pinocytic and smooth-membrane vesicles, whereas the organelles participating in synthetic processes are poorly developed; their function is most likely related to active solute transport.     

The ultrastructure of basal cells of rat and dog prostate

Summary The ultrastructure of the basal cells of rat lateral and ventral prostate and of dog prostate has been studied. Basal cells from both species appear as undifferentiated cells, characterised by a lack of cytoplasmic organelles and a poorly developed Golgi complex and endoplasmic reticulum. The presence of cytoplasmic filaments and micropinocytosis is not considered to be sufficient evidence to assume any similarity to myoepithelium, as has been previously suggested. Basal cells are instead considered to be precursors of secretory epithelial cells.The authors wish to express their gratitude to the Tenovus Organisation for their generous financial support. This work was also supported by a grant from the Medical Research Council No. G974/304B. One of them (FS) was supported by the British Council     

Location matters: the endoplasmic reticulum and protein trafficking in dendrites

Neurons are highly polarized, but the trafficking mechanisms that operate in these cells and the topological organization of their secretory organelles are still poorly understood. Particularly incipient is our knowledge of the role of the neuronal endoplasmic reticulum. Here we review the current understanding of the endoplasmic reticulum in neurons, its structure, composition, dendritic distribution and dynamics. We also focus on the trafficking of proteins through the dendritic endoplasmic reticulum, emphasizing the relevance of transport, retention, assembly of multi-subunit protein complexes and export. We additionally discuss the roles of the dendritic endoplasmic reticulum in synaptic plasticity.     

Fine structure of the abdominal neural fat-body sheath in the stick insect (Carausius morosus,Br.)

The neural fat-body sheath surrounding the abdominal ventral nerve cord of Carausius morosus has been examined by light and electron microscopy. A perineural chamber between the ventral nerve cord and the sheath is present in the ganglionic regions, but in the interconnective regions the sheath directly covers the neural lamella. The sheath is differentiated into secretory cells with abundant granular endoplasmic reticulum and many mitochondria and storage cells with lipid droplets and granules presumed to be glycogen. The whole sheath is pervaded with tracheoblast cells and associated tracheal and tracheolar tubules. Recent evidence suggests that this sheath may have little power of ionic regulation. The function of the sheath, deduced from the fine structure described here, appears to be to serve the nutritional needs of the central nervous system. Why a sheath of this type appears to be confined to herbivorous insects with unusual haemolymph cationic balance is still unexplained.     

The parathyroid gland of the woodchuck (Marmota monax): a study of seasonal variations in the chief cells

The ultrastructure of the parathyroid chief cell in the woodchuck, Marmota monax, was studied during the four seasons of the year. Spring chief cells have stacks of granular endoplasmic reticulum, prominent multiple Golgi zones and many clumped mitochondria. Summer cells resemble those seen in the spring but the mitochondria are associated with stacks of granular endoplasmic reticulum. Multiple areas of stacked granular endoplasmic reticulum characterize the fall chief cells. Their Golgi zones are large and are associated with many dense core secretory granules. Lipoid vacuoles are frequently noted. Winter chief cells have secretory granules and phagolysosomes (dense bodies). Some of these cells contain stacked arrays of granular endoplasmic reticulum associated with mitochondria, others have only short segments. The above morphological findings are discussed in relation to those in other hibernators, the parafollicular (C) cell, and to the cyclic seasonal activities of the woodchuck.     

Destructive and restorative processes of the liver in rats under intensive physical loading

The ultrastructure of rat liver cells after running exercise was investigated. When rats were trained for a month and sacrificed immediately after the last exercise it was revealed that the number of liver cells mitochondria increased, but many of them had alterations: mitochondria became swollen, had lucid matrix. There were some variations in degree of alterations between different mitochondria: a) in the same hepatocyte, b) in different hepatocytes of the same animal, that was connected with individual sensitivity of organelles on the levels of the cell and of the organ. Rough endoplasmic reticulum bore few ribosomes. Glycogen was absent. There were abundant vesicles of smooth endoplasmic reticulum, autophagic vacuoles and peroxisomes in the liver cell cytoplasm. Adaptation of rat liver to the exercise programme becomes evident by 1.5 month of exercise. Mitochondria and rough endoplasmic reticulum were numerous and of normal structure. There were many peroxisomes and glycogen granules in the cytoplasm of hepatocyte. The presence of large autophagic vacuoles in the cytoplasm of some hepatocytes were obviously connected with more rapid destruction of some organelles, than in control.     

Fine structure of the human foetal testis

Summary Thirteen male human foetuses ranging in crown-rump length from 29 to 212 mm (ages 8–27 weeks) were studied. Four developmental phases are distinguished. 1. The predifferentiation phase (below 8 weeks): The interstitium contains only undifferentiated mesenchymal cells. 2. The differentiation phase (8–14 weeks): Leydig cells develop and gradually fill the space between the germ cords. 3. The maturity phase (14–18 weeks): The interstitium occupies more than one half of the total area in the testis sections and is filled with mature foetal Leydig cells. 4. The involution phase (18–40 weeks): Most of the Leydig cells gradually degenerate and disappear.The foetal Leydig cells are packed with tubular agranular endoplasmic reticulum (AER). Islets of parallel granular ER membranes and other organelles are embedded in the AER. The mitochondria vary in shape and form, the cristae being mainly tubular. Some mitochondria like organelles contain electron dense inclusions. Dark membrane bound bodies of variable form and resembling the Golgi cisternae are present in most cells. Reinke crystals are never found in the foetal cells. In degenerating Leydig cells the AER appears in vesicular form, membranous whorls are seen in some of them and the cell membrane seems to rupture finally, and cytoplasmic material protrudes outside the cells. The fine structure of the mature foetal Leydig cells is suggested to reflect signs of human chorionic gonadotrophin stimulation.This investigation was supported by the Damon Runyon Memorial Fund (DRG-940) and by the Sigrid Jusélius Foundation.     

Intracellular transfer of phospholipids in the yeast, Saccharomyces cerevisiae

In Saccharomyces cerevisiae, unlike in higher eukaryotic cells, most of the reactions involved in phospholipid biosynthesis occur both in mitochondria and in the endoplasmic reticulum. Some of the key enzymes involved, however, are restricted to one compartment. Thus, the formation of phosphatidylethanolamine by decarboxylation of phosphatidylserine occurs only in mitochondria, while phosphatidylcholine synthesis via methylation of phosphatidylethanolamine is restricted to microsomes. When yeast cells were pulse labelled with [3H]serine,[3H] phosphatidylethanolamine formed in mitochondria was found not only in the organelle but also, with even higher specific radioactivity, in the endoplasmic reticulum. Translocation of phosphatidylethanolamine between organelles was blocked immediately after poisoning cells with cyanide, azide and fluoride. Part of the [3H]phosphatidylcholine formed in the endoplasmic reticulum by methylation of [3H]phosphatidylethanolamine was transferred to mitochondria. This process continued in deenergized cells, although at a lower rate as compared to metabolizing cells. This result indicates rapid movement of both phosphatidylethanolamine and phosphatidylcholine requires metabolic energy, but that phosphatidylinositol-specific phospholipid transfer protein that has been found in saccharomyces cerevisiae (Daum, G. and Paltauf, F. (1984) Biochim. Biophys. Acta 784, 385-391). The mechanism of movement of phospholipids from internal membranes to the cell surface was studied with temperature-sensitive secretory mutants (Schekman, R. (1982) Trends Biochem. Sci. 7, 243-246) of Saccharomyces cerevisiae. A shift from the permissive to the restrictive temperature, which blocks the flow of vesicles involved in the secretion of proteins, had no effect on the transfer of phosphatidylinositol to the plasma membrane.     

Interrelationships of endoplasmic reticulum, mitochondria, intermediate filaments, and microtubules--a quadruple fluorescence labeling study.

To study the interrelationships of endoplasmic reticulum, mitochondria, intermediate filaments, and microtubules, we have developed a quadruple fluorescence labeling procedure to visualize all four structures in the same cell. We applied this approach to study cellular organization in control cells and in cells treated with the microtubule drugs vinblastine or taxol. Endoplasmic reticulum was visualized by staining glutaraldehyde-fixed cells with the dye 3,3'-dihexyloxacarbocyanine iodide. After detergent permeabilization, triple immunofluorescence was carried out to specifically visualize mitochondria, vimentin intermediate filaments, and microtubules. Mitochondria in human fibroblasts were found to be highly elongated tubular structures (lengths up to greater than 50 microns), which in many cases were apparently fused to each other. Mitochondria were always observed to be associated with endoplasmic reticulum, although endoplasmic reticulum also existed independently. Intermediate filament distribution could not completely account for endoplasmic reticulum or mitochondrial distributions. Microtubules, however, always codistributed with these organelles. Microtubule depolymerization in vinblastine treated cells resulted in coaggregation of endoplasmic reticulum and mitochondria, and in the collapse of intermediate filaments. The spatial distributions of organelles compared with intermediate filaments were not identical, indicating that attachment of organelles to intermediate filaments was not responsible for organelle aggregation. Mitochondrial associations with endoplasmic reticulum, on the other hand, were retained, indicating this association was stable regardless of endoplasmic reticulum form or microtubules. In taxol-treated cells, endoplasmic reticulum, mitochondria, and intermediate filaments were all associated with taxol-stabilized microtubule bundles.     

Death receptor ligation triggers membrane scrambling between Golgi and mitochondria

Subcellular organelles such as mitochondria, endoplasmic reticulum (ER) and the Golgi complex are involved in the progression of the cell death programme. We report here that soon after ligation of Fas (CD95/Apo1) in type II cells, elements of the Golgi complex intermix with mitochondria. This mixing follows centrifugal dispersal of secretory membranes and reflects a global alteration of membrane traffic. Activation of apical caspases is instrumental for promoting the dispersal of secretory organelles, since caspase inhibition blocks the outward movement of Golgi-related endomembranes and reduces their mixing with mitochondria. Caspase inhibition also blocks the FasL-induced secretion of intracellular proteases from lysosomal compartments, outlining a novel aspect of death receptor signalling via apical caspases. Thus, our work unveils that Fas ligand-mediated apoptosis induces scrambling of mitochondrial and secretory organelles via a global alteration of membrane traffic that is modulated by apical caspases.     

Morphology and ultrastructure of the convoluted gland in the ant Dinoponera australis (Hymenoptera: Formicidae)

The morphology and fine structure of the convoluted gland inside the venom reservoir of the ponerine ant Dinoponera australis (Hymenoptera: Formicidae) are described. The cells of the convoluted gland can be divided into 3 major groups: (1) epithelial cells, (2) glandular cells with end apparatus secreting into the tubule inside the convoluted gland, and (3) glandular cells with end apparatus secreting directly into the venom reservoir. A fourth group of cells belonging to the venom gland of this ant is also discussed as (4) secretory cells of the free tubule (not a part of the convoluted gland). The epithelial cells in the convoluted gland do not have many organelles. Most cells of group 3 are characterized by numerous mitochondria. In some of these cells, the mitochondria possess tubular cristae. Tubule cells of group 2 inside the convoluted gland, possess little rough endoplasmic reticulum when compared with cells of group 4, situated in the free tubule.     

Intracellular levels and distribution of Ca2+ in digitonin-permeabilized cells

Digitonin and other saponins can be used to selectively permeabilize the plasma membrane of a wide variety of cells without significantly affecting the gross structure and function of Ca2+-sequestering organelles such as mitochondria and endoplasmic reticulum. These characteristics have allowed digitonin to be used in the determination of the intracellular levels and distribution of Ca2+, as well as the measurement of Ca2+ fluxes by organelles "in situ". Studies conducted with several different types of digitonin-permeabilized cells indicate that the endoplasmic reticulum functions as a high affinity and low-capacity intracellular Ca2+ buffer, whereas mitochondria operate as a relatively low affinity but high capacity Ca2+ buffering system. However, recent findings suggest that mitochondria have a comparable affinity for net Ca2+ uptake in the presence of physiological concentrations of polyamines. The use of permeabilized cells has also been important in the identification of the endoplasmic reticulum as a site at which the recently discovered second messenger inositol trisphosphate acts to bring about an increase in the cytosolic free Ca2+ concentration. Thus, the selective permeabilization of cells with digitonin and its analogues has been a powerful yet simple tool in the study of intracellular Ca2+ homeostasis.     

Thiamine pyrophosphatase activity in the axonal smooth endoplasmic reticulum of neurosecretory neurons

Summary Neurosecretory cells of the supraoptic-neurohypophysial system of normal mice were investigated with the use of the cytochemical reaction for thiamine pyrophosphatase (TPPase) at the ultrastructural level. In the hypothalamic perikarya dense lead precipitates occur within the cisterns of the mature face of the Golgi apparatus, these being the cisterns that give rise to neurosecretory granules (NSG). Smooth endoplasmic reticulum is occasionally confluent with TPPase-positive Golgi cisterns. Along axons, within swellings, and within terminals distinct profiles of TPPase-positive tubules and cisterns are revealed, apparently part of a network of axonal smooth endoplasmic reticulum (AER). Some NSG appear to be confluent with AER. NSG with TPPase-positive tubular protrusions (likely vestiges of AER) are seen. Apart from reaction product (lead precipitate), the AER often contains an electron dense substance optically similar to that of NSG. TPPase-containing AER is often associated with mitochondria. Profiles of electron-lucent, precipitate-free tubules and cisterns are occasionally seen alongside reactive AER. Optimal TPPase activity in the AER occurs at pH 7.0–7.4, whereas in the Golgi complex intense marking is in the range of pH 6.0–8.5. A faint peppering of precipitate occasionally appears in the AER in controls (incubation medium without substrate), but neither in density nor in extent is this comparable to the reaction product seen after incubation in the presence of TPP. Preliminary comparison has been made between the AER revealed by the TPPase reaction, and that visualized after heavy metal impregnation according to the method of Alonso and Assenmacher (1978a). The nature of the close association between NSG and AER, and the possible roles of this membrane system in neurosecretory cells is discussed.Abbreviations AER axonal smooth endoplasmic reticulum - NSG neurosecretory granules - TPPase thiamine pyrophosphatase - SON supraoptic nucleus Research supported in part by a grant from the Israel Academy of Sciences to M.C.We thank Mrs. Ilana Sabnay for excellent technical assistance     

Ultrastructureofthe human intervertebral disc. I. Changes in notochordal cells with age

We examined nucleus pulposus notochordal cells of individuals ranging in age from the eighth week of fetal life to 32 years of age. With increasing age, notochordal cell structure changed, as did the cell-to-cell relationships and the cell-to-matrix relationships. All notochordal cells contained normal organelles, including welldeveloped endoplasmic reticulum, but, in addition, fetal notochordal cells demonstrated an unusual relationship between rough endoplasmic reticulum and mitochondria: elements of the rough endoplasmic reticulum encircled almost every mitochondrion. Fetal notochordal cells contained large amounts of glycogen, while older cells had much smaller glycogen deposits. Cytoplasmic filaments were observed in cells of all ages. The cells formed tightly packed clusters in the fetus with little, if any, extracellular matrix between individual cells. Cells separated from each other with age and by the twenty-first week of fetal life, only slender strands of cytoplasm connected them. Previous light microscopic studies described notochordal cells as ‘physaliphorus’ cells since they appeared to contain large cytoplasmic vacuoles. However, electron microscopy showed that these apparent vacuoles consist of extracellular matrix surrounded by cells or cell processes. The structure of notochordal cells and their persistence in the nucleus pulposus after fetal life suggest that they may have a significant role in the formation and maintenance of the nucleus pulposus.     

Fine structure of the wet,detached cell stigma of the orchid Dendrobium speciosum Sm.

Summary The stigmatic surface of the orchid Dendrobium speciosum is a cup containing detached cells suspended in a mainly carbohydrate mucilage. The fine structure of the detached cells and their organelles is indicative of secretory cells. The cells contain numerous mitochondria with well-developed cristae, dictyosomes containing extensive cisternae, an extensive network of rough and smooth endoplasmic reticulum and free polysomes throughout. There are many amyloplasts in the vicinity of the nucleus. Vesicles are seen arising from the dictyosomes and endoplasmic reticulum. The plasmalemma is undulating, and vesicles can be seen in its vicinity, giving the typical appearance of a granulocrine secretory system. Cetylpyridinium chloride (CPC) fixation to immobilise acidic carbohydrates detected a highly electron-opaque layer surrounding each cell and globules dispersed through the cell wall. The walls of the detached cells show irregular surface projections which are the remains of pitfields. Biochemical analysis showed that carbohydrates and arabinogalactan proteins are major components of the mucilage.     

新疆医科大学基础医学院组织胚胎学教研室

目的:观察国人胚胎三叉神经节细胞分化及发育过程。方法:取水囊引产18-36周国人胎儿三叉神经节,HE染色及透射电镜观察。结果:18-20周胎儿三叉神经节神经元排列紧密,胞质少,可见到数量不多的线粒体,且其内几乎看不到嵴,其它细胞器少。25周时,线粒体嵴变长,粗面内质网雏形出现,有纵形小管出现;27周时可观察到成熟的高尔基复合体,32周后,线粒体、粗面内质网等细胞器发育趋于成熟。到33周电镜下可见溶酶体;36周时细胞内各种细胞器结构和功能基本完善。结论:人胚胎三叉神经节细胞发育过程中随胎龄增加,其结构和功能逐步完善,32～36周(8～9月)是细胞的分化发育重要时期。     

Histochemical localization of adenosine triphosphatase activity in thymus: A light microscopical and ultrastructural study

Summary Ultrastructural localization of ATPase at high pH in the presence of Ca²⁺ showed that activity in thymocyte precursors was stronger than in mature thymocytes. The activity was localized in the nuclear envelope, rough endoplasmic reticulum, Golgi apparatus and mitochondria. The difference in activity was attributed to a marked decrease in ATPase-containing organelles, mainly the endoplasmic reticulum in the mature thymocytes. This appears to be related to the proliferative activity of the cells rather than to the immunological maturity of the thymocytes. A very strong activity, also localized in the same organelles, was present in the macrophages and interdigitating cells which might have a secretory function and possibly contribute to thymocyte maturation. The Ca²⁺—ATPase activity in the nuclear envelope—endoplasmic reticulum system suggests that these may be the sites for storage and regulation of cytoplasmic calcium.