Volume Of Rough Endoplasmic Reticulum Research Articles

Endoplasmic reticulum positioning and partitioning in mitotic HeLa cells.

Cell division serves to distribute chromosomes and organelles into two daughter cells, but the mechanism of rough endoplasmic reticulum (RER) segregation in animal cell mitosis is poorly understood. Here we study the distribution of RER in mitotic HeLa cells and its relation to the cytoskeleton. At metaphase, the RER was located in the cell cortex and was most concentrated in two locations. Close to the plasma membrane the RER was closely associated with cortical actin, and after treatment with Latrunculin A RER elements retracted to the deep cortex and became more tubular. Positioning was therefore dependent on cortical F-actin. Deeper in the cortex cisternae were wrapped tightly around the contours of the spindle body and orientated along microtubules close the spindle poles. Stereology revealed a close correlation between RER volume and cell volume in telophase daughter cells. These results suggest that the RER is positioned at the outer and inner regions of metaphase cortex by association with cytoskeleton. This arrangement combined with a disposition in concentric layers, deep to the plasma membrane, appears to distribute the RER evenly in the cortex and may help to couple quantities of RER and cell constituents.

XBP1: a link between the unfolded protein response, lipid biosynthesis, and biogenesis of the endoplasmic reticulum.

When the protein folding capacity of the endoplasmic reticulum (ER) is challenged, the unfolded protein response (UPR) maintains ER homeostasis by regulating protein synthesis and enhancing expression of resident ER proteins that facilitate protein maturation and degradation. Here, we report that enforced expression of XBP1(S), the active form of the XBP1 transcription factor generated by UPR-mediated splicing of XBP1 mRNA, is sufficient to induce synthesis of phosphatidylcholine, the primary phospholipid of the ER membrane. Cells overexpressing XBP1(S) exhibit elevated levels of membrane phospholipids, increased surface area and volume of rough ER, and enhanced activity of the cytidine diphosphocholine pathway of phosphatidylcholine biosynthesis. These data suggest that XBP1(S) links the mammalian UPR to phospholipid biosynthesis and ER biogenesis.

Effect of hypoglycemic stress on the pars intermedia of the mouse pituitary gland: an ultrastructural analysis.

The present study was made to clarify the relationship between functions of the pars intermedia of the mouse pituitary gland and hypoglycemic stress. Morphometrical analysis of the ultrastructures of the pars intermedia cells showed (1) a rise in the percentage volume of rough endoplasmic reticulum (r-ER) indicative of an increase in protein synthesis, (2) an increase in the number of Golgi granules per unit Golgi area showing an induction of granule-forming activity and (3) a decrease in the numerical density of secretory granules reflecting a release of the secretory granules. These findings suggest that hypoglycemic stress induced by daily treatment with insulin or restriction of food intake was able to elicit heightened secretory activity of the pars intermedia cells of the mouse pituitary gland. However, acute hypoglycemic stress induced by food deprivation did not cytologically affect the pars intermedia. These observations suggest that repeated hypoglycemic stress, rather than acute hypoglycemic stress, may be a natural physiological stimulus of the pars intermedia of the mouse pituitary gland.

Structure and ultrastructure of the epididymis of the viviparous lizard during the annual hormonal cycle: Changes of the epithelium related to secretory activity

This study deals with the structure and ultrastructure of the epithelial cells of the lizard (Lacerta vivipara Jacquin) epididymis as related to secretory activity. The epithelium contains only two types of cells, secretory cells and basal cells. The secretory cells undergo an annual cycle which has been divided into 10 stages. In its most active secretory state, epithelium forms 65.3% of the organ volume. The secretory cell is a tall columnar cell (from 55 ± 3.4 μm to 74.3 ± 2.4 μm height) with a basal nucleus and a supranuclear cytoplasm almost entirely occupied by numerous large secretory granules (5 to 7 μm in diameter). At the ultrastructural level, secretory cells contain rough endoplasmic reticulum (RER), Golgi complex, and secretory granules at various stages of synthesis before being discharged into the lumen. Each granule is membrane-limited and contains a spherical electron dense central core and a peripheral vacuole which varies in density. The secretory cell originates from small cubic cells (13.8 ± 0.7 μm) with few organelles (stage 1). The height of the cell increases gradually and free ribosomes appear first (stage 2), followed by scarce elements of RER (stage 3). The step preceding the secretion period (stage 4) is characterized by a conspicuous increase in volume of RER and Golgi complex. From stage 7 to stage 10, the cell undergoes a dramatic involution. After a transient hypertrophy of the RER, numerous autophagic vacuoles invade the cytoplasm. This degeneration can lead to a complete lysis of the cell and to its rebuilding after elimination of the greatest part of the cytoplasm. The volume of the epithelium falls to 15.6% of the total volume. With antibodies raised against the protein family which constitutes the main part of the secretion (L proteins of 19 kDa), it is shown by immunohistochemistry that these proteins are concentrated into secretory granules which are discharged into the lumen to finally bind to the heads of the spermatozoa.

Morphometric Study of the Rat Exocrine Pancreas After Diversion of Bile and Pancreatic Juice From the Intestine

The effects of 6 h of diversion of bile and pancreatic juice from the intestine on the ultrastructure of rat pancreatic acinar cells were studied by morphometric procedures. After diversion the volume of zymogen granules decreased markedly, representing a reduction of 77%. The volume of autophagic vacuoles increased twofold after diversion. The volume of rough endoplasmic reticulum and Golgi apparatus was not different from that of control. It has been proved by electron microscopic morphometry that the degree of reduction of zymogen granules was similar to that after stimulation by exogenous cholecystokinin or introduction of trypsin inhibitor to the duodenum. This suggests that hypersecretion caused by diversion is due to failure of a negative feedback regulation normally induced by proteases found in pancreatic juice. An increased number of autophagic vacuoles suggests an increase of organelle turnover due to heightened secretory activity of acinar cells.

Ultrastructural distribution of morphology of the mammary gland with observations on the size fat droplets in milk of the Weddell seal Leptonychotes weddelli (Pinnipedia)

Ultrastructural observations were made of the non‐lactating and lactating mammary gland of the Weddell seal, and measurements of several cell components were compared with those in other species to determine whether there are any morphological modifications within the gland to explain the unusual milk composition and very rapid growth of sucking young in this species.The mammary parenchyma in non‐lactating and lactating Weddell seals is almost identical morphologically to that found in other mammals. Although the relative volumes of most organelles are similar to those in other eutherians, the relative volume of rough endoplasmic reticulum (RER) is reduced in the Weddell seal. In addition, the absolute and relative volumes of Golgi vacuoles are smaller in the Weddell seal, probably associated with the low lactose and water content of the milk. The synthesis and secretion of milkspecific proteins and fat droplets by mammary secretory cells in the Weddell seal appear to be identical to other eutherians. Relatively small numbers of fat droplets less than 1 μm diameter are present in epithelial cells, alveolar lumina and milk samples, and there is a far greater contribution by large fat droplets to the total fat volume of Weddell seal milk than milk from other mammals.

Enhanced responsiveness of lactotrophs in ectopic pituitaries to bromocryptine and estrone acetate.

Intrasellar and transplanted pituitaries removed from the same rats were studied using light microscopy, immunocytology, electron microscopy and ultrastructural morphometry following treatment with bromocryptine and/or estrone acetate. Ectopic lactotrophs of rats treated with bromocryptine showed an increase in storage granule size and number, which was not observed in the lactotrophs of corresponding intrasellar pituitaries. In lactotrophs of intrasellar and ectopic pituitaries, treatment with estrone acetate caused a decrease of storage granule size, while rough endoplasmic reticulum (RER) and Golgi region volume density increased. When rats were treated with a combination of bromocryptine and estrone acetate, intrasellar lactotrophs exhibited increased volume density and diameter size in forming granules as well as increased RER volume density. In ectopic lactotrophs, combined treatment led to a decrease in RER, volume densities of Golgi region and forming granules, as well as increased storage granule size. It can be concluded that ectopic lactotrophs were more sensitive to the inhibiting effects of bromocryptine treatment than intrasellar lactotrophs. Intrasellar lactotrophs were more susceptible to estrone acetate than bromocryptine treatment. As a result, the increased responsiveness of ectopic lactotrophs to estrone acetate was less conspicuous.

Intracellular dynamics in pituitary mammotropes throughout the rat estrous cycle. II. Changes in synthetic and secretory organelles.

The organellar dynamics within mammotropes (prolactin secreting cells) of the anterior pituitary were examined using morphometry throughout the four-day rat estrous cycle. Two predominant periods of maximal organellar activity were found. The first period, which occurred during proestrus, resulted in two peaks of serum PRL at 6 pm and 12 m proestrus, while the second occurred during middiestrus-2 and resulted in an increase of pituitary PRL, but not a major serum PRL peak. The mitochondrial volume rose prior to that of other organelles during early proestrus, rising 110% from 4 am late diestrus-2 to 6 pm proestrus. However, the number of mitochondria per cell remained constant throughout the cycle. The volumes of rough endoplasmic reticulum (RER) and Golgi complex reached maximal proportions at 8 pm and 12 m proestrus, respectively. The RER volume was 153% greater than at 4 am late diestrus-2, while the Golgi complex had increased by 200%. We suggest that changes in the RER and Golgi complex volumes were the result of two processes: the synthesis of new membrane and the swelling of existing complexes. This study further substantiated that the serum peak of PRL at 6 pm proestrus is the result of stored mature granules being released, whereas the PRL peak at 12 m proestrus is due to the immediate release of hormone without any storage.

A morphometric study on the pars intermedia of the hypophysis during impairment of the renin-angiotensin-aldosterone system in sodium depleted mice

Fine structural alterations were investigated in cells of the pars intermedia of the pituitary of mice treated for four weeks with (a) a sodium deficient diet, (b) a sodium deficient diet mixed with propranolol (renin-inhibitor), (c) a sodium deficient diet combined with propranolol and amino-glutethimide (corticosterone 18-hydroxylase inhibitor), and (d) a sodium deficient diet combined with propranolol, aminoglutethimide and dexamethasone. The number of secretory granules decreased from 5.0/mum2 in the normal control of 2.4/mum2 in all four experimental groups suggesting that the cells in treated groups had reached an equilibrium in the production and release of secretory granules during the chronic treatments. The number of immature Golgi granules per unit Golgi area was 0.91 in the control, while this value rose to 3.29 (3.62 fold of the control), 4.37 (4.8 fold), 4.94 (5.43 fold) and 5.16 (5.67 fold) respectively in the four experimental groups. In these groups a good correlation was observed between the number of immature granules and the percent volume of rough endoplasmic reticulum (r=0.985, p less than 0.01). The present study suggests that the pars intermedia contains an unidentified pituitary factor (or factors) essential for aldosterone biosynthesis.

Effect of starvation on nuclear bodies and rough endoplasmic reticulum in the bovine hepatocyte

The frequency of simple nuclear bodies and the relative volume of rough endoplasmic reticulum was determined in hepatocytes of normal lactating cows and of lactating cows starved for 6 days. Starvation resulted in a highly significant decrease in frequency of simple nuclear bodies and in the relative volume of rough endoplasmic reticulum. It is suggested that simple nuclear bodies are normal nuclear organelles which can respond to physiological changes.

Quantification of ultrastructural changes in the 'melanocyte-stimulating hormone cell' of the pars intermedia of the pituitary of Xenopus laevis, produced by change of background colour.

SUMMARY The fact that the transfer of amphibians between black and white backgrounds causes the 'melanocyte-stimulating hormone (MSH) cells' of the pars intermedia of the pituitary to undergo considerable morphological change has been established for some time. The application of morphometric techniques to the 'MSH cells' of Xenopus has permitted the quantitative analysis of these changes at the ultrastructural level. Of the nine classes of organelle selected for analysis in these cells, three, namely nucleus, plasma membrane and dense bodies, showed no statistically significant changes. The remaining classes of organelle all showed significant changes in the percentage of the total cell volume that they occupied, although not all the organelles changed at the same rate. Transfer of animals from a white to a black background for up to 12 days was associated with increase in the percent volume of rough endoplasmic reticulum, Golgi membranes, Golgi granules and mitochondria and with a decrease in the percent volume of the fibrous granules. Return of animals to a white background after 6 days on a black background produced a reversal of the above changes with return to, or close to, white background (control) levels. This quantitative ultrastructural approach also highlights discrepancies in both the rate and magnitude of the changes in some of the organelles and related non-morphological parameters previously reported, e.g. the size of the rough endoplasmic reticulum and the rate of incorporation of labelled amino acid into protein; or the numbers of fibrous granules and the levels of detectable pituitary MSH. Some possible interpretations of these discrepancies are discussed.

Ultrastructural-morphometric analysis of rat liver cell after orotic acid administration

One week of feeding rats with a diet rich in orotic acid induces different alterations in liver cells. By morphometry we could observe: (1) An augmentation of volume of the single mitochondrion together with a reduction in number of this organelle per hepatocyte; (2) A decrease in volume density of rough endoplasmic reticulum; (3) A smaller number of microbodies per hepatocyte, the single microbody showing an unchanged volume; (4) A decrease in volume density of lysosomes; (5) An increased volume density of fat vacuoles. The mitochondrial alterations and the changes in volume of rough endoplasmic reticulum are suspected to represent a morphological counterpart to the purine nucleotide deficiency induced by orotic acid. The number of microbodies is reduced without degenerative forms appearing. Therefore, a deficient synthesis of this organelle is suggested by these experiments.