Three-dimensional structure of the osmium-impregnated golgi apparatus as seen in the high voltage electron microscope

Osmication in an unbuffered aqueous solution of osmium tetroxide allows the forming face of the Golgi apparatus to be labeled in many cell types. This property was utilized to study the spatial configuration of this organelle by examining stereopairs of the same field taken at 1,000 KV after tilting a thick (1 to 7 μUm) section of ? 7° or + 7° from the original (0°) position. When examined in 1 μm thick sections at magnifications ranging from 13,000 to 18,000 times, the osmic acid-impregnated element of the Golgi apparatus of ganglion nerve cells, Leydig cells or Sertoli cells takes the appearance of a single layered polygonal network of tubules. This network can only be seen at electron microscope magnifications and is referred to as the primary network or structure of the forming face of the Golgi apparatus. When 2 to 7 μm thick sections are examined under progressively lower magnifications, the details of the primary structure remain discernible but become less conspicuous. The osmiophilic portion of the Golgi apparatus now extends over large areas of the cytoplasm to form an extensive continuous structure. This structure which is in the range of visibility of the light microscope is referred to as the secondary network or structure of the forming face. In ganglion nerve cells, the secondary structure consists of a perinuclear network showing slender projections reaching the nucleus and wider expansions approaching the cell surface; in the Leydig cells it appears as an ovoid structure located at one pole of the nucleus whereas in Sertoli cells it forms a cylindrical structure located in the main shaft of the cytoplasm and extending from the nucleus towards the lumen of the seminiferous tubule. Thus the forming face of the Golgi apparatus displays a primary structure; the tubular roughly polygonal network, which is similar in the three cell types and a secondary structure which varies from cell to cell.     

The cell population in pancreatic islets of amphisbaenidae — a light and electron microscopic study

A diversity of cell types have been found in the pancreatic islets of three species of Amphisbaenidae in a light and electron microscopic investigation. The A cells have been characterized as having phosphotungstic acid hematoxylin and orange G positive secretory granules which are electron opaque and 450–500 mμ, in diameter. The B cells possess aldehyde fuchsin reactive granules which are slightly larger than A granules, approximately 550 mμ, and have a variety of profiles in the electron microscope. The D cells are characterized as being fast green positive and argyrophilic in the light microscope, and in the electron microscope have small, 200–300 mμ, secretory granules with a core of moderate electron opacity. In D cells the Golgi apparatus is more highly developed than in A or B cells. Bipes islets contain a presumptive fourth cell type possessing large secretory granules with irregular profiles and focal internal densities. An additional cell type, found in Amphisbaena manni and Bipes, has small, electron opaque granules.     

Three-dimensional structure of cytidine monophosphatase reactive trans-Golgi elements in spinal ganglion cells of the rat

In order to analyse, at the electron microscope level, the three-dimensional configuration of the trans compartment of the Golgi apparatus rat dorsal root ganglia were treated to demonstrate cytidine monophosphatase (CMPase) activity. The localization of enzymatic activity in the Golgi apparatus varied according to cell types. In type A and C cell, CMPase was exclusively located in the transmost sacculotubular element, whereas in type B cells all the saccules of the stacks forming the Golgi ribbon and the trans-Golgi networks were impregnated. Numerous dense bodies seen at proximity were also CMPase positive. In 3 μm thick sections of type A cells examined at low magnification, the impregnated element was scattered throughout the cytoplasm and never formed a continuous structure. In type B cells, the strongly reactive trans-Golgi networks did not follow the entire length of the impregnated Golgi ribbon but were preferentially located in the concavity of its arched portions. At higher magnification and in all cell types some tubular portions of the trans-Golgi networks took the apperance of spheroidal cage-like structures, the CMPase positive anastomotic tubules forming the bars of the cage. Anastomotic tubules separated from the trans-Golgi networks formed fenestrated spheres, while nearby CMPase-reactive dense bodies exhibited a paler hilus. These observations were taken to indicate that in ganglion cells, some CMPase positive dense bodies, presumably lysosomes, formed by fragmentation of the trans-Golgi networks.     

Stereological analysis of normal rabbit pancreatic islets

Stereological methods were applied to obtain morphometric data related to pancreatic islets of Langerhans in the normal rabbit. By light microscopy, it was found that 1 mm³ of pancreatic parenchyma contained 47.7 islets, constituting 2.2% of its volume. Approximately 69% of the islets had diameters less than 80 μm; 31% were greater than 80 μm. The former group of islets, however, composed only 13% of the volume of the endocrine pancreas and the latter group, 87%. Using electron microscopy, a unit volume of islet tissue was observed to consist of 86% beta cells, 7.7% alpha cells, and 2.2% delta cells. The average beta-cell volume was 1260 μm³ and its cytoplasm consisted of 52.6% matrix, 12.7% rough endoplasmic reticulum, 10.2% secretory granules, 7.8% mitochondria, and 3.3% Golgi apparatus. A typical beta cell contained 662 mitochondria, intermediate (10-nm) filaments whose length totalled 50 mm, and 9,200 secretory granules with a ratio of four mature granules to each immature or “pale” granule. Within alpha and beta cells, three parameters were used for the quantitation of organelles or their component parts: (1) volume; (2) surface; and (3) numerical densities. In the beta cell, the surface densities of rough endoplasmic reticulum and Golgi membranes exceeded, by two- or threefold, their counterparts in alpha cells. Similarly, the number of beta-cell mitochondria exceeded by 30% that of alpha cells; but beta-cell mitochondrial volume was twice that of the alpha cell, as were surface densities of both inner and outer mitochondrial membranes. Volume and surface densities of secretory granules within beta cells were half the values obtained for alpha cells. An alpha cell contained three times the number of granules present in a beta cell.     

Three-dimensional structure of cytidine monophosphatase reactive trans-Golgi elements in spinal ganglion cells of the rat.

In order to analyse, at the electron microscope level, the three-dimensional configuration of the trans compartment of the Golgi apparatus rat dorsal root ganglia were treated to demonstrate cytidine monophosphatase (CMPase) activity. The localization of enzymatic activity in the Golgi apparatus varied according to cell types. In type A and C cells, CMPase was exclusively located in the transmost sacculotubular element, whereas in type B cells all the saccules of the stacks forming the Golgi ribbon and the trans-Golgi networks were impregnated. Numerous dense bodies seen at proximity were also CMPase positive. In 3 microns thick sections of type A cells examined at low magnification, the impregnated element was scattered throughout the cytoplasm and never formed a continuous structure. In type B cells, the strongly reactive trans-Golgi networks did not follow the entire length of the impregnated Golgi ribbon but were preferentially located in the concavity of its arched portions. At higher magnification and in all cell types some tubular portions of the trans-Golgi networks took the appearance of spheroidal cage-like structures, the CMPase positive anastomotic tubules forming the bars of the cage. Anastomotic tubules separated from the trans-Golgi networks formed fenestrated spheres, while nearby CMPase-reactive dense bodies exhibited a paler hilus. These observations were taken to indicate that in ganglion cells, some CMPase positive dense bodies, presumably lysosomes, formed by fragmentation of the trans-Golgi networks.     

The Golgi apparatus in the acinar cells of the developing embryonic pancreas: I. Morphology and enzyme cytochemistry

The Golgi apparatus apparatus of pancreatic acinar cells of rat embryos was studied during development from day 13 through day 20 of gestation. The morphological and enzyme cytochemical patterns varied characteristically in the course of cell differentiation. (1) A pronounced system of “rigid lamellae” characterized the area near the trans face of the Golgi stacks in the protodifferentiated and early phases of the differentiated states; by contrast, “rigid lamellae” were sparse in the terminal period of gestation. (2) Reaction product of acid phosphatase labeled the “rigid lamellae” in the protodifferentiated state, was extended across the majority of the stacked cisternae in the early differentiated state, but was restricted to the trans side again in the later periods of cell differentiation. (3) The early phase of the differentiated state was characterized by the tight association of the endoplasmic reticulum and Golgi cisternae on the trans side; the close spatial relationship of the two compartments was lessened after production of secretion granules had started. The findings are in line with those of recent studies on the Golgi organization in some other types of cells in different functional states, and they present the embryonic pancreatic tissue as another model for demonstrating the high flexibility of the Golgi complex. In agreement with the patterns previously found in the absorptive cells of the small intestine, the present results show that the close associations of the endoplasmic reticulum and cisternae of the trans Golgi side predominate in the early stages of cell differentiation.     

The ultrastructural features of secretory cells of some endocrine glands in aging

In the electron microscopic investigation of the secretory cells of adenohypophysis, adrenal cortex, adrenal medulla and pancreatic islets from the adult and old Wistar male rats, certain age-related ultrastructural features have been found. Age changes appeared to be more pronounced in the thyrotrophs, somatotrophs and gonadotrophs of the adenohypophysis and in zona glomerulosa and zona reticularis spongiocytes of the adrenal cortex. They consisted of atrophy of the Golgi apparatus, appearance of the cytoplasmic vacuoles, lipid and lipofuscin granules, secondary lysosomes and damage of the inner mitochondrial membrane. Parallel to these, hypertrophy of the Golgi apparatus and rough endoplasmic reticulum, formation of giant mitochondria and presence of a great number of secretory cells in the cellular cytoplasm were noted in zona fasciculata spongiocytes and chromaffin cells of the adrenal medulla, and in beta cells of the pancreatic islets during aging thus evidencing for the adaptive changes in the ultrastructure of these cells. However, no appreciable age changes have been observed in the ultrastructure of the adrenocorticotropic cells of the adenohypophysis.     

Granule formation and polarity of the Golgi apparatus in neutrophil granulocytes of the rat

The formation of granules in neutrophil (heterophil) progenitor cells was examined with the electron microscope in sections of rat bone marrow fixed in 2% glutaraldehyde and postfixed with reduced osmium (Karnovsky: Proceedings of the 11th Meeting, American Society of Cell Biologists, Abstr. 284, p. 146, 1971). The cells were also osmicated in 2% osmium tetroxide for 36 hours at 37 degrees C to outline the osmiophilic element usually observed on the cis-face of the stacks of saccules of the Golgi apparatus of various cell types. In myeloblasts, which do not produce granules, the cis-osmiophilic element (CE) was found on the concave face of the C-shaped Golgi stacks. In promyelocytes the CE was present on the convex aspect of the C-shaped stacks, while the primary (azurophilic) granules formed in relation to elements on the concave aspects of the stacks. In myelocytes, the situation was reversed: the CE was found on the concave face of the Golgi stacks, while the secondary (specific) granules were seen forming in relation to elements on the convex aspect of the stacks. Finally, in metamyelocytes and mature neutrophils in which no granule formation took place, the appearance on Golgi stacks varied: they were either flat or C-shaped. The CE was indiscriminately found on one face or the other of the flat Golgi stacks of metamyetocytes and on the convex or concave faces of the C-shaped Golgi stacks of mature neutrophils. Using the cis-osmiophilic-element as a marker of the cis-face of the stacked Golgi elements, it thus appeared that despite marked changes in the configuration and orientation of the stacks of the cis-trans polarity of the stacked elements was maintained throughout granulopoiesis. In addition the primary and secondary granules that appeared sequentially in promyelocytes and myelocytes were both seen to form in relation to trans-elements of the Golgi apparatus.     

In ''undifferentiated'' PC12 cells, GERL is not segregated from the Golgi apparatus

Summary The present study examines the endocytosis of conjugates of horseradish peroxidase (HRP) with ricin and wheat germ agglutinin (WGA) in rat adrenal pheochromocytoma cells (PC12 line) cultured in the absence of nerve growth factor (NGF). In these cells acid phosphatase (ACPase) activity is not confined to a single cisterna and vesicles at the transaspect (mature face) of the Golgi apparatus which correspond to GERL of cultured neurons, neuroblastoma and other cell types. But ACPase is found in several cisternae of the Golgi apparatus as well as in lysosomes. On the other hand, thiamine pyrophosphatase activity, is found in a typical location within two or three cisternae of the Golgi apparatus near its transaspect. Following adsorptive endocytosis of HRP-labelled lectins (ricin-HRP or WGA-HRP) into PC12 cells, a reaction product is seen in dense bodies as well as in small vesicles and tubules throughout the cytoplasm, at the periphery of large vacuoles, in smooth and coated vesicles and tubules near the Golgi apparatus and in anastomosing tubules. The cisternae of the Golgi apparatus are not involved in the endocytosis of lectin-HRP. We concluded that in PC12 cells grown without NGF, unlike the case of cultured neurons and neuroblastoma cells, GERL is not segregated from the Golgi apparatus by either ACPase cytochemistry, or by the functional criterion of endocytosis of lectin-HRP conjugates.     

Cell polarity changes and migration during early development of the avian peripheral auditory system

The intracellular location of organelles was studied in avian embryos immediately before and during the initial detachment of cells from the dorsoanterolateral wall of the otocyst, using light and electron microscopy. The Golgi apparatus was silver-impregnated, and its location within the otic epithelium was determined quantitatively. The present study demonstrates that a sub-population of cells of the dorsoanterolateral otic epithelium changes the intracellular location of its organelles, particularly the Golgi apparatus and the centrosome, from an apical to a basal position. Concomitantly, cells lose specializations characteristically present at apical (tight junctions, microvilli) and basal (basal lamina) surfaces. At basolateral cell surfaces, filopodia form ahead of the Golgi apparatus and centrosome and penetrate the previously continuous underlying basal lamina. Thereafter, cells detach from the otocyst and migrate medially toward the hind-brain. Thus, concomitant with changes in surface polarity, the cells that comprise the dorsoanterolateral wall of the otocyst undergo profound changes in the intracellular location of their organelles, especially the Golgi apparatus and the centrosome, so that by the time cells detach from the otic epithelium a reversal in their "normal" internal polarity has occurred. We suggest that the change in cell polarity may be related to the mechanisms that allow cells to leave the otocyst.     

Studies on co-localization of 7B2 and pancreatic hormones in normal and tumoural islet cells

Summary The distribution of protein 7B2, a protein with structural characteristics of GTP-binding proteins, has been studied in normal pancreatic islets and in a series of 70 pancreatic endocrine tumours with emphasis on the co-localization of 7B2 and the different pancreatic hormones. Although all cell types of normal islets were found to store 7B2, variations from intense expression to absence of reaction were seen within each cell type. In particular, B cells showed intense immunostaining for 7B2 in small compact islets and weak or no staining in larger islets with lobular arrangement. Pancreatic polypeptide (PP) cells expressed 7B2 intensely in the PP-rich area of ventral embryological origin, but were mostly non-reactive in the PP-poor area. The A cells, located along intralobular blood vessels, were more frequently immunoreactive for 7B2 than those at the periphery of the islets. Immuno-electron microscopy revealed a preferential localization of 7B2 in secretory granules of islet cells, with more intense localization in the peripheral halo of alpha granules. Benign islet cell tumours more frequently expressed 7B2 than their malignant counterparts. Although often expressed in a lower number of tumour cells than the tumour-specific hormone, 7B2 was usually co-localized with the latter. In contrast, no relationship was found with the localization of proinsulin. It is concluded that 7B2 is a non-permanent component of the cell granule compartment, probably involved in events related to exocytosis and without relationship to intracellular prohormone processing.     

Immunocytochemical and ultrastructural heterogeneities of normal and glibenclamide stimulated pancreatic beta cells in the rat

When studied morphologically in semi-thin sections in the rat in vivo, pancreatic beta cells displayed heterogeneous immunoreactivities for insulin and amylin, depending on the islet size and the intra-islet position of the beta cells. In larger islets, cortical beta cells (beta cells with contacts with all islet cell types and with the exocrine parenchyma) which are located in the periphery were more densely immunostained for insulin and amylin than medullary beta cells (beta cells with contacts only with other beta cells) which are located in the centre of the islet. Ultrastructurally, these findings were accompanied by differences in the number of secretory granules and mitochondria. Beta cells in small islets and at extra-islet sites exhibited a dense immunoreactivity. After administration of glibenclamide, immunoreactivities for insulin and amylin were diminished in a time-dependent manner, decreasing first in medullary and thereafter in cortical beta cells of larger islets. Ultrastructurally, the beta cells exhibited the typical signs of stimulation. A minority of beta cells in small islets and all beta cells in extra-islet locations remained unchanged. Thus pancreatic beta cells under basal and stimulatory conditions in vivo exhibit heterogeneity in hormone content and in ultrastructural features. These differences may represent the basis for a functional heterogeneity of the insulin secretory response of the individual beta cell both in vivo and in vitro in states of normal and impaired insulin secretion. As heterogeneity was observed only among beta cells in islets, while single beta cells surrounded by acinar cells exhibited no changes in insulin immunoreactivity, interactions between beta cells as well as between beta cells and other endocrine cells may be critical for expression of heterogeneity within the beta cell population.     

Membrane differentiation in the golgi apparatus of mammalian urinary bladder epithelium

The endomembrane system in superficial and intermediate epithelial cells of mammalian urinary bladder was studied by cytochemistry, thin-section and freeze-fracture electron microscopy to determine the sites where special forms of membrane differentiation first appear. Glutaraldehyde-resistant NADH-ferricyanide reductase, distinctive 11–12 nm intramembrane particles (IMP), and asymmetry of membrane leaflets served as markers of membrane maturation. The three markers were specifically associated with the maturing face of Golgi apparatus and were absent from the remainder of the endomembrane system. Activity of this enzyme was associated with the lateral regions of the maturing face, fusiform vesicles, and the plasmalemma. Asymmetric unit membrane (AUM) plaques were not observed in the Golgi apparatus per se but were present in immature fusiform vesicles that had not detached from the maturing face. When freeze-fracture replicas and thin sections were compared, randomly arranged 11–12 nm IMP first appeared in maturing face membranes that were adjacent to clusters of “free” polyribosomes in the Golgi apparatus region. The proximity of these polyribosomes suggests that they may be related to the coincident appearance of the 11–12 nm IMP in the maturing face membrane. Our observations support the hypothesis that membranes undergo differentiation during “flow” through compartments of the endomembrane system. The lateral regions of the maturing face of the Golgi apparatus appear to be a critical location for the morphogenesis of plasma membranes in urinary bladder.     

Distribution of cell types of the islets of Langerhans throughout the pancreas of the Chacma baboon

Biopsies of the pancreas head, tail, and uncinate regions of four baboons were processed for immunocytochemical (ICC) studies by using avidin-biotin-peroxidase label for light microscopy (LM). Toluidine-blue- or methylene-blue-stained 0.5-micron sections of nonosmicated resin-embedded tissue were viewed to locate areas of suitable islets. For ICC investigations, batches 10 microns apart of ten consecutive 1-micron sections throughout ten islets from each of the three regions were immunolabelled for LM. Four slides in each batch were immunolabelled consecutively for insulin, glucagon, somatostatin, and pancreatic polypeptide, the fifth acting as one of the range of controls in each batch. The number of each of the four cell types was counted in at least ten immunolabelled islets from each of the pancreas heads, uncinate portions, and tails. The uncinate region and not the head, as in most mammals, was found to contain significantly higher numbers of pancreatic polypeptide (PP) cells and lower numbers of A (glucagon) and D (somatostatin) cells (P less than .001). The PP cells occurred in clumps and not as described in other mammals as part of the mantle of A, D, and PP cells. PP and A cell numbers were significantly different for each region (P less than .001), being lowest in the head for PP and in the uncinate process for A cells. D cell distribution was similar to that of the A cells whilst a significantly smaller number of B (insulin) cells was found in the tail compared with other regions (P less than .001).     

Adenovirus mediated gene transduction of primarily isolated mouse islets

Expansion of pancreatic islet cell populations, especially the beta cells, using a currently available ex vivo gene transfer technology is important to develop cell therapies to treat Type I diabetes. In this study, we evaluated adenovirus mediated gene transfer efficiency in primarily isolated mouse islet cells in two types of culture conditions: freshly isolated suspended islets and cultured islets with monolayer formation. A recombinant replication deficient adenovirus vector encoding a green fluorescence protein (GFP) cDNA, Ad/ CMV-GFP, was used in the present transduction experiments. Rat 804G derived extracellular matrix (804G-ECM) and 3-isobutyl-1-methylxanthine (IBMX) were used to facilitate monolayer formation of the isolated mouse pancreatic islets. Suspended islets were transfected with Ad/CMV-GFP at more than 95% efficiency. However, analysis of immunohistochemical stains for insulin and glucagon in thin sliced sections of the islets revealed that GFP expression was localized just in the outer cells of the islets, almost all of which were glucagon positive alpha-cells. The beta-cells existing at the inner area of the suspended islets were GFP negative. In contrast, under the condition of the islets in monolayer formation cultures, all of the islet cells including the beta-cells were efficiently infected with Ad/CMV-GFP. To achieve an efficient adenoviral gene transfer to the pancreatic beta-cells, monolayer formation of the islets is critical. Such culture conditions were facilitated by combining 804G-ECM with IBMX.     

Role of microtubules in the organization of the Golgi complex and the secretion of collagen secretory granules by periodontal ligament fibroblasts

Fibroblasts of the periodontal ligament (PDL) of the mouse exhibit a high degree of cytoplasmic and functional polarity. This polarity is dependent upon an elaborate system of microtubules. The location of the microtubular arrays and the observed effects of colchicine administration suggest that microtubules play an important role in maintaining the organization of the Golgi complex and its functional relationship to the rough endoplasmic reticulum. Smooth-walled intermediate vesicles, apparently derived from the rough endoplasmic reticulum, are aligned along microtubules at the immature face of the Golgi apparatus, and mature secretory granules are closely related to microtubules at the mature face of the Golgi apparatus. In distal cell processes the granules are closely parallel to microtubules and on occasion bridge-like attachments from granules to microtubules were noted. This relationship of secretory granules to microtubules, the lack of granule storage, and the effects of colchicine on granule secretion suggests that microtubules are part of a mechanism for collagen granule translocation from the Golgi complex to the cell periphery.     

Increased pancreatic islet mass is accompanied by activation of the insulin receptor substrate-2/serine-threonine kinase pathway and augmented cyclin D2 protein levels in insulin-resistant rats

It is well known that glucocorticoids induce peripheral insulin resistance in rodents and humans. Here, we investigated the structural and ultrastructural modifications, as well as the proteins involved in beta-cell function and proliferation, in islets from insulin-resistant rats. Adult male Wistar rats were made insulin resistant by daily administration of dexamethasone (DEX; 1mg/kg, i.p.) for five consecutive days, whilst control (CTL) rats received saline alone. Structure analyses showed a marked hypertrophy of DEX islets with an increase of 1.7-fold in islet mass and of 1.6-fold in islet density compared with CTL islets ( P <  0.05). Ultrastructural evaluation of islets revealed an increased amount of secreting organelles, such as endoplasmic reticulum and Golgi apparatus in DEX islets. Mitotic figures were observed in DEX islets at structural and ultrastructural levels. Beta-cell proliferation, evaluated at the immunohistochemical level using anti-PCNA (proliferating cell nuclear antigen), showed an increase in pancreatic beta-cell proliferation of 6.4-fold in DEX islets compared with CTL islets ( P <  0.0001). Increases in insulin receptor substrate-2 (IRS-2), phosphorylated-serine-threonine kinase AKT (p-AKT), cyclin D₂ and a decrease in retinoblastoma protein (pRb) levels were observed in DEX islets compared with CTL islets ( P <  0.05). Therefore, during the development of insulin resistance, the endocrine pancreas adapts itself increasing beta-cell mass and proliferation, resulting in an amelioration of the functions. The potential mechanisms that underlie these events involve the activation of the IRS-2/AKT pathway and activation of the cell cycle, mediated by cyclin D₂. These adaptations permit the maintenance of glycaemia at near-physiological ranges.     

人胰岛内分泌细胞的双重免疫组化研究

本文采用单酶双标法对成人胰岛内分泌细胞进行了双重免疫组化染色．结果发现：（1）成人胰岛为鞘型胰岛．即A、D细胞位于胰岛的周围部形成鞘．且二者间存在位置分布上的一致性；B细胞位于胰岛的中央部。（2）即使由于有结缔组织隔将胰岛分隔成不同的“亚单位”．其每一“亚单位”的周围部仍为A、D细胞，中央部仍为B细胞。     

Coexistence of glucagon and pancreatic polypeptide in human and rat pancreatic endocrine cells

Pancreatic islet cells containing both glucagon and pancreatic polypeptide simultaneously (glucagon/PP cells) were identified in the rat and human normal pancreas using immunocy-tochemical staining on consecutive serial sections and double-immunolabeling techniques on the same sections. Numerous glucagon/PP cells were found at the periphery of the islets in all regions of the pancreas, particularly in the rat. As a whole, these bipeptide-containing cells appeared in higher proportions than the cells secreting glucagon or PP separately. Double immunogold labeling performed on both surfaces of the thin tissue sections allowed differentiation between the glucagon/PP cells and the single-labeled glucagon or PP cells at the ultra-structural level. The pancreatic glucagon/PP cells displayed the morphological characteristics of either A cells or PP cells. Both peptides were found in the same secretory granules of the glucagon/PP cells and, in the human pancreas, the glucagon/PP cells displayed secretory granules with a dense core in which both peptides were rather concentrated. The coexistence of glucagon and PP is assumed to originate from the simultaneous expression of the two different genes in the same cell and suggests that the cellular processing through the rough en-doplasmic reticulum-Golgi apparatusgranule secretory pathway for both peptides takes place in parallel.     

Macrophage migration inhibitory factor deficiency protects pancreatic islets from cytokine-induced apoptosis in vitro

During pathogenesis of diabetes, pancreatic islets are exposed to high levels of cytokines and other inflammatory mediators that induce deterioration of insulin-producing beta cells. Macrophage migration inhibitory factor (MIF) plays a key role in the onset and development of several immunoinflammatory diseases and also controls apoptotic cell death. Because the occurrence of apoptosis plays a pathogenetic role in beta cell death during type 1 diabetes development and MIF is expressed in beta cells, we explored the influence of MIF deficiency on cytokine-induced apoptosis in pancreatic islets. The results indicated clearly that elevated MIF secretion preceded C57BL/6 pancreatic islets death induced by interferon (IFN)-γ + tumour necrosis factor (TNF)-α + interleukin (IL)-1β. Consequently, MIF-deficient [MIF-knock-out (KO)] pancreatic islets or islet cells showed significant resistance to cytokine-induced death than those isolated from C57BL/6 mice. Furthermore, upon exposure to cytokines pancreatic islets from MIF-KO mice maintained normal insulin expression and produced less cyclooxygenase-2 (COX-2) than those from wild-type C57BL6 mice. The final outcome of cytokine-induced islet apoptosis in islets from wild-type mice was the activation of mitochondrial membrane pore-forming protein Bcl-2-associated X protein and effector caspase 3. In contrast, these apoptotic mediators remained at normal levels in islets from MIF-KO mice suggesting that MIF absence prevented initiation of the mitochondrial apoptotic pathway. Additionally, the protection from apoptosis was also mediated by up-regulation of prosurvival kinase extracellular-regulated kinase 1/2 in MIF-KO islets. These data indicate that MIF is involved in the propagation of pancreatic islets apoptosis probably via nuclear factor-κB and mitochondria-related proteins.