Reticulum Of Epithelial Cells Research Articles

CYP311A1 in the anterior midgut is involved in lipid distribution and microvillus integrity in Drosophila melanogaster.

Lipids are either taken up from food sources or produced internally in specialized tissues such as the liver. Among others, both routes of lipid metabolism involve cytochrome P450 monooxygenases (CYPs). We sought to analyze the function of Cyp311a1 that has been shown to be expressed in the midgut of the fruit fly Drosophila melanogaster. Using a GFP-tagged version of CYP311A1that is expressed under the control of its endogenous promoter, we show that Cyp311a1 localizes to the endoplasmic reticulum in epithelial cells of the anterior midgut. In larvae with reduced Cyp311a1 expression in the anterior midgut, compared to control larvae, the apical plasma membrane of the respective epithelial cells contains less and shorter microvilli. In addition, we observed reduction of neutral lipids in the fat body, the insect liver, and decreased phosphatidylethanolamine (PE) and triacylglycerols (TAG) amounts in the whole body of these larvae. Probably as a consequence, they cease to grow and eventually die. The microvillus defects in larvae with reduced Cyp311a1 expression are restored by supplying PE, a major phospholipid of plasma membranes, to the food. Moreover, the growth arrest phenotype of these larvae is partially rescued. Together, these results suggest that the anterior midgut is an import hub in lipid distribution and that the midgut-specific CYP311A1 contributes to this function by participating in shaping microvilli in a PE-dependent manner.

Progressive Depletion of Rough Endoplasmic Reticulum in Epithelial Cells of the Small Intestine in Monosodium Glutamate Mice Model of Obesity.

Chronic obesity is a known risk factor for metabolic syndrome. However, little is known about pathological changes in the small intestine associated with chronic obesity. This study investigated cellular and subcellular level changes in the small intestine of obese mice. In this study, a mouse model of obesity was established by early postnatal administration of monosodium glutamate. Changes in body weight were monitored, and pathological changes in the small intestine were evaluated using hematoxylin-eosin and Nissl staining and light and electron microscopy. Consequently, obese mice were significantly heavier compared with controls from 9 weeks of age. Villi in the small intestine of obese mice were elongated and thinned. There was reduced hematoxylin staining in the epithelium of the small intestine of obese mice. Electron microscopy revealed a significant decrease in and shortening of rough endoplasmic reticulum in epithelial cells of the small intestine of obese mice compared with normal mice. The decrease in rough endoplasmic reticulum in the small intestine epithelial cells of obese mice indicates that obesity starting in childhood influences various functions of the small intestine, such as protein synthesis, and could impair both the defense mechanism against invasion of pathogenic microbes and nutritional absorption.

Maleate modifies apical endocytosis and permeability of endoplasmic reticulum membranes in kidney tubular cells.

Previous studies have shown that histochemical modifications of the endoplasmic reticulum in epithelial cells might be related to their transport function. We have examined the effect of sodium maleate, which produces generalized transport derangement reminiscent of Fanconi syndrome, on the organization, morphology and enzyme activities of endoplasmic reticulum in rat kidney cells. The osmium impregnation technique has revealed that apical vacuoles increase in volume and in number in most proximal tubule cells, and contain osmium deposits. Osmium impregnation of the endoplasmic reticulum is much reduced. In vitro studies, performed with isolated microsomes, show NADPH cytochrome c reductase activity in both normal and maleate-treated rats. As revealed by vanadate, Ca+-ATPase activity in isolated microsomes is unnaffected by maleate but the vanadate-insensitive or passive component of calcium uptake increases particularly later in the response. Therefore, the remaining calcium uptake in the presence of vanadate is indeed passive; in vivo maleate administration also appears to increase the passive entry of calcium into the microsomal compartment. The morphological and histochemical alterations of the endoplasmic reticulum cisternae occur rapidly and with a similar time course to the transport defects, suggesting that this organelle plays a role in transcellular transport. Maleate may directly affect the endoplasmic reticulum membranes whereby passive permeability to calcium is increased. The endocytotic apparatus and possibly exocytosis phenomena are modified by maleate as shown by the increased vacuolization and the presence of black osmium deposits in vacuoles.

Three-dimensional organization of a transcellular tubulocisternal endoplasmic reticulum in epithelial cells of Reissner's membrane in the guinea-pig

The ultrastructure of the epithelial cells of Reissner's membrane (membrana vestibularis) in the guinea-pig is described following vascular perfusion with glutaraldehyde of live, anaesthetised and artificially respirated animals. Postfixation in a solution containing OsO4 and potassium ferricyanide revealed a well-developed tubulocisternal endoplasmic reticulum, not previously described, the continuity of which has been mapped by serial sectioning and reconstruction. Large disc-shaped subsurface cisternae lining the cell membrane, but separated from it by a space approximately 10 nm wide, are in continuity with the smooth endoplasmic reticulum, forming an elaborated transcellular canalicular pathway. This structure is compared to that found in solute-transporting epithelia, e.g., renal proximal tubule, gall bladder, small intestine and choroid plexus. The fixation method used in the present study is compared to other techniques used for preservation of Reissner's membrane. Each epithelial cell of Reissner's membrane is endowed with one kinocilium, one to four multivesicular bodies, and a number of intercalated bodies. The functional significance of the canalicular pathway is discussed.

Morphological evidence for an endoplasmic reticulum origin of milk lipid globules obtained using lipid-selective staining procedures

Mammary tissue from lactating rats was stained for electron microscopic examination by three methods which selectively stain lipids by increasing osmium deposition. Regions of endoplasmic reticulum in epithelial cells were observed to have areas where the reticular membrane was distended with material with the same staining characteristics as intracellular lipid droplets. Very small droplets, which stained as did larger lipid droplets, were observed in the immediate vicinity of endoplasmic reticulum cisternae, frequently in regions where the cisternal membrane appeared to be distorted or degraded. These observations are consistent with the hypothesis that intracellular lipid droplet precursors of milk lipid globules originate by accretion of triacylglycerols on or between the monolayer leaflets of endoplasmic reticulum membrane and are released as very small droplets from the endoplasmic reticulum into the cytoplasm.

An unusual modification of endoplasmic reticulum in epithelial cells of the mouse ascending colon.

A rarely occurring structure that is apparently a modification of endoplasmic reticulum was observed in the epithelial cells of the ascending colon of the mouse. The structure consists of a stack of 3 to 15 parallel cisterna-like elements separated by about 67 nm. The stacked cisternae usually are located adjacent to the basal end of the nucleus or in the region between nucleus and basal cell membrane. Top and bottom cisternae of many of the stacks have patent lumens and their outer membranes are lined by ribosomes. Most frequently, middle cisternae have attenuated lumens in their central regions. In some instances the width of the cisternal lumens is similar throughout. Closely apposed pairs of cisternae also occur. Some stacks have a concentric configuration. The intercisternal space contains tightly packed vesicles (38 nm) arranged in a hexagonal array. Many of the vesicles are connected to the membranes of the cisternae by stalk-like projections. The vesicles also occur between the nuclear envelope and the adjacent parallel cisternae. Mitochondria are situated close to each stack.