STUDIES ON THE ENDOPLASMIC RETICULUM
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Abstract:
A series of representative cell types including avian fibroblasts, and macrophages; rabbit mesothelia, endothelia, and nephron epithelia; and rat glandular epithelia (parotid) were studied comparatively in vitro and in situ with the electron microscope. Cells in vitro were examined in whole mounts and in sections whereas cells in situ were observed exclusively in sections. It was found that an endoplasmic reticulum similar to that previously described in cultured material is present in situ in all cell types examined. Modifications in its appearance introduced by the sectioning technique were discussed and explained. The observations showed in addition that the endoplasmic reticulum is a network of cavities which may enlarge into relatively vast, flattened vesicles here described as cisternae.Keywords:
Cell type
A septum-rich fraction was prepared from Triehophyton mentagrophytes, and the ultrastructural investigation of septa was carried out by shadowing and thin section electron microscopy before and after enzymatic and/or alkaline treatments. Tri-lamellar structure, consisting of an electron lucid middle layer and two outer electron dense layers, was observed by thin section electron microscopy. By shadowing electron microscopy, the surface ultrastructure of septa exhibited a randomly orientated microfibrillar network structure, which may correspond to the electron dense outer layers of the septum observed in thin section preparations. However, shadowed septa after papain digestion revealed a spiral arrangement of microfibrils consisting of rodlet-like units, which disappeared during chitinase treatment. This spiral structure may therefore be composed primarily of chitin. It was suggested that this spirally arranged microfibrils may correspond to the electron lucid middle layer observed in thin section preparations.
Thin section
Morphology
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Comparison with the findings in the cells of other plants and animals showed that the endoplasmic reticulum in the root apex ofFagopyrum has the same general character and function as in other biological objects, i.e. in secretory processes and especially in this case in the transport of the substances produced. Detailed studies of the morphology and activity of the endoplasmic reticulum showed some functional differences which are characteristic for this object. The endoplasmic reticulum participates apparently in the transport of the mass of known but functionally and nomenclatorically controversial formations which here are called dense bodies. Dense bodies exist inFagopyrum in a considerable amount as compared to other objects. Frequent contact of the dense bodies with the ends of the endoplasmic reticulum, contact with the endoplasmic retieulum passing through the plasmodesm, accumulation of the dense bodies along the cell wall and in proximal distance of the plasmodesms and intensive staining of some plasmodesms was observed. The dense vacuoles in this object represent dilated spaces of the endoplasmic reticulum which apparently have the function of reservoirs of the dense mass. The endoplasmic reticulum in the calyptra cells appears to participate in the formation of the cell walls. This object differs hereby from others, where the participation of the Golgi apparatus has been observed in this function.
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The distribution of glucose-6-phosphatase activity in rat hepatocytes during a period of rapid endoplasmic reticulum differentiation (4 days before birth-1 day after birth) was studied by electron microscope cytochemistry. Techniques were devised to insure adequate morphological preservation, retain glucose-6-phosphatase activity, and control some other possible artifacts. At all stages examined the lead phosphate deposited by the cytochemical reaction is localized to the endoplasmic reticulum and the nuclear envelope. At 4 days before birth, when the enzyme specific activity is only a few per cent of the adult level, the lead deposit is present in only a few hepatocytes. In these cells a light deposit is seen throughout the entire rough-surfaced endoplasmic reticulum. At birth, when the specific activity of glucose-6-phosphatase is approximately equal to that of the adult, nearly all cells show a positive reaction for the enzyme and, again, the deposit is evenly distributed throughout the entire endoplasmic reticulum. By 24 hr postparturition all of the rough endoplasmic reticulum, and in addition the newly formed smooth endoplasmic reticulum, contains heavy lead deposits; enzyme activity at this stage is 250% of the adult level. These findings indicate that glucose-6-phosphatase develops simultaneously within all of the rough endoplasmic reticulum membranes of a given cell, although asynchronously in the hepatocyte population as a whole. In addition, the enzyme appears throughout the entire smooth endoplasmic reticulum as the membranes form during the first 24 hr after birth. The results suggest a lack of differentiation within the endoplasmic reticulum with respect to the distribution of glucose-6-phosphatase at the present level of resolution.
Cytochemistry
Glucose 6-phosphatase
Reticulum
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Endoplasmic reticulum stress as a new concern during the pathogenesis of alcoholic liver disease(ALD)has entered the people's vision.Endoplasmic reticulum stress caused by the accumulation of misfolded and unfolded proteins in the endoplasmic reticulum.Appropriate stress was benefical to recovery of intracellular environment,however,serious and persistent stress may lead to apoptosis.Hepatocytes are one of the most sensitive cells,which contain abundant endoplasmic reticulum.Existing study has indicated that endoplasmic reticulum contributed to the development of ALD in cell and animal models.In this review,we summaried the role of endoplasmic stress in the pathogenesis of ALD.
Pathogenesis
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Unfolded or misfolded proteins accumulating in endoplasmic reticulum and the disturbance of cells homeostasis will result in the endoplasmic reticulum stress.Endoplasmic reticulum stress to a certain extent lead to the restoration of cells internal environment.However,if the stress is too strong and lasting,the function of endoplasmic reticulum will be damaged and cell apoptosis will present.As one of the most sensitive cells of endoplasmic reticulum stress,pancreatic β-cells have an abundance of endoplasmic reticulum.Apoptosis of insulin-secreting cells induced by endoplasmic reticulum stress participate in the onset of diabete mellitus.
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Thioflavin
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Electron microscopy of hepatocytes in both normal rat liver and rat liver treated to induce hyperplasia of smooth endoplasmic reticulum shows that autophagic vacuoles and residual bodies (types of lysosomes) are continuous with endoplasmic reticulum.
Reticulum
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Endoplasmic reticula,widely distributed within cells,are important places for cell synthesis of proteins,lipids and sugars,and are closely related to transport and exchange of materials.Endoplasmic reticulum endoplasmic reticulum stress induced by steady imbalances(Endoplasmic reticulum stress,ERS),persistent stress can lead to apoptosis.A number of studies show endoplasmic reticulum stress and various liver diseases are closely related.This article reviews the correlation between endoplasmic reticulum stress and pathogenesis of liver disease.
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