scholarly journals Co-ordination between membrane phospholipid synthesis and accelerated biosynthesis of cytoplasmic ribonucleic acid and protein

1970 ◽  
Vol 116 (4) ◽  
pp. 617-630 ◽  
Author(s):  
J. R. Tata
Keyword(s):  
Growth Hormone ◽  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Time Course ◽  
Seminal Vesicles ◽  
Membrane Phospholipid ◽  
Phospholipid Synthesis ◽  
Membrane Phospholipids ◽  
Short Period ◽  
Microsomal Membranes

1. The rate of synthesis of membrane phospholipid was studied in rat liver and seminal vesicles by following the incorporation of [32P]orthophosphate, [14C]choline and [14C]glycerol. Particular emphasis was laid on the endoplasmic reticulum, which was fractionated into smooth microsomal membranes, heavy rough membranes, light rough membranes and free polyribosomes. 2. Phospholipid labelling patterns suggested a heterogeneity in the synthesis and turnover of the different lipid moieties of smooth and rough endoplasmic membranes. The major phospholipids, phosphatidylcholine and phosphatidylethanolamine, were labelled relatively rapidly with 32P over a short period of time whereas incorporation of radioisotope into the minor phospholipids, sphingomyelin, lysolecithin and phosphatidylinositol proceeded slowly but over a longer period of time. 3. The incorporation of orotic acid into RNA and labelled amino acids into protein of the four submicrosomal fractions was also studied. 4. Rapid growth of the liver was induced by the administration of growth hormone and tri-iodothyronine to hypophysectomized and thyroidectomized rats and by partial hepatectomy. Growth of seminal vesicles of castrated rats was stimulated with testosterone propionate. 5. The rate of labelling of membrane phospholipids was enhanced in all major subcellular particulate fractions (nuclear, mitochondrial and microsomal) during induced growth. However, it was in the rough endoplasmic reticulum that the accumulation of phospholipids, RNA and protein was most marked. The effect of hormone administration was also to accelerate preferentially the labelling with 32P of sphingomyelin relative to that of phosphatidylcholine or phosphatidylethanolamine. 6. Time-course analyses showed that, in all four growth systems studied, the enhancement of the rate of membrane phospholipid synthesis coincided with the rather abrupt increase in the synthesis of RNA and protein of the rough endoplasmic reticulum. Growth hormone and tri-iodothyronine administered to hypophysectomized rats had additive effects in all the biosynthetic processes. The latent period of action of each hormone was maintained so that two waves of proliferation of endoplasmic reticulum occurred if the hormones were administered simultaneously. 7. It is concluded that there is some mechanism in the cell that tightly co-ordinates the formation of membranes, especially those of the endoplasmic reticulum, when an increased demand is made for protein synthesis.

Heterogeneity of phospholipid synthesis in rat liver endoplasmic reticulum during proliferation of smooth membranes

1976 ◽  
Vol 22 (1) ◽  
pp. 173-197
Author(s):  
J.A. Higgins
Keyword(s):  
Endoplasmic Reticulum ◽  
Uniform Distribution ◽  
Specific Activity ◽  
Intact Cell ◽  
Smooth Endoplasmic Reticulum ◽  
Membrane Phospholipid ◽  
Phospholipid Synthesis ◽  
Protein Ratio ◽  
Cytochemical Localization ◽  
Heterogeneous Distribution

During proliferation of smooth endoplasmic reticulum (SER) induced by phenobarbital the specific activity of acyltransferases of the smooth microsomes increases, there is a transient rise in the phospholipid/protein ratio of these membranes, and an increased incorporation of [14C]glycerol into smooth-membrane phospholipid. Microsomes separated into subfractions on 2 gradients exhibited a heterogeneous distribution of these characteristics, indicating a non-uniform distribution of the site of phospholipid synthesis in the ER under these conditions. Cytochemical localization of acyltransferases on whole liver and smooth and rough microsomes confirmed this heterogeneity, and indicated that the distribution of this activity was not restricted to any morphologically distinct site in the ER of the intact cell. After 4 days of phenobarbital treatment the increased membrane is restricted to lighter subfractions and is similar in distribution to that of increased acyltransferase activity. These results indicate that the synthesis of membrane phospholipid and the growth of the SER in response to phenobarbital is not uniform but occurs at randomly dispersed sites in the SER while proteins may be added preferentially at these sites resulting in a final uniform distribution.

Cotyledon cell development in Arabidopsis thaliana during reserve deposition

1992 ◽  
Vol 70 (1) ◽  
pp. 151-164 ◽  
Author(s):  
S. G. Mansfield ◽  
L. G. Briarty
Keyword(s):  
Arabidopsis Thaliana ◽  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Volume Fraction ◽  
Biological Membrane ◽  
Lipid Body ◽  
Cell Development ◽  
Volume Fractions ◽  
Short Period ◽  
Cotyledon Cell

Cotyledon cell development in Arabidopsis thaliana L. during reserve deposition has been analyzed qualitatively and quantitatively. Development has been related to the previously defined time scale for Arabidopsis, hours after flowering. Between 144 and 216 h after flowering the major cell changes in the cotyledon are an increase in the cell volume, a decrease in the volume fraction of cytoplasm and plastids, and an increase in lipid and vacuole volume fractions. The endoplasmic reticulum and dictyosome volume fractions are high during early reserve formation (144 – 168 h after flowering) but decrease significantly thereafter. Evidence as to the origin of the storage lipid is inconclusive, although a dual involvement of plastids and rough endoplasmic reticulum is a likely theory. The 3-nm lipid body membrane, which allows the bodies to retain their individuality during accumulation, is probably a half-unit biological membrane, derived from closely associated rough endoplasmic reticulum cisternae. Much of the evidence obtained in this study indicates that both the endoplasmic reticulum and dictyosomes are involved in protein synthesis and transport to the vacuole. The accumulation of reserves occurs in a well-defined and relatively short period during late embryogenesis (144–216 h after flowering). Key words: Arabidopsis, cotyledons, embryogenesis, reserve deposition, stereology.

scholarly journals Mobility of ribosomes bound to microsomal membranes. A freeze-etch and thin-section electron microscope study of the structure and fluidity of the rough endoplasmic reticulum.

1977 ◽  
Vol 72 (3) ◽  
pp. 530-551 ◽  
Author(s):  
G K Ojakian ◽  
G Kreibich ◽  
D D Sabatini
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Thin Section ◽  
Rough Endoplasmic Reticulum ◽  
Binding Sites ◽  
Lateral Displacement ◽  
Homogeneous Distribution ◽  
Antibody Treatment ◽  
Section Electron ◽  
Microsomal Membranes

The lateral mobility of ribosomes bound to rough endoplasmic reticulum (RER) membranes was demonstrated under experimental conditions. High-salt-washed rough microsomes were treated with pancreatic ribonuclease (RNase) to cleave the mRNA of bound polyribosomes and allow the movement of individual bound ribosomesmfreeze-etch and thin-section electron microscopy demonstrated that, when rough microsomes were treated with RNase at 4 degrees C and then maintained at this temperature until fixation, the bound ribosomes retained their homogeneous distribution on the microsomal surface. However, when RNase-treated rough microsomes were brought to 24 degrees C, a temperature above the thermotropic phase transition of the microsomal phospholipids, bound ribosomes were no longer distributed homogeneously but, instead, formed large, tightly packed aggregates on the microsomal surface. Bound polyribosomes could also be aggregated by treating rough microsomes with antibodies raised against large ribosomal subunit proteins. In these experiments, extensive cross-linking of ribosomes from adjacent microsomes also occurred, and large ribosome-free membrane areas were produced. Sedimentation analysis in sucrose density gradients demonstrated that the RNase treatment did not release bound ribosomes from the membranes; however, the aggregated ribosomes remain capable of peptide bond synthesis and were released by puromycin. It is proposed that the formation of ribosomal aggregates on the microsomal surface results from the lateral displacement of ribosomes along with their attached binding sites, nascent polypeptide chains, and other associated membrane proteins; The inhibition of ribosome mobility after maintaining rough microsomes at 4 degrees C after RNase, or antibody, treatment suggests that the ribosome binding sites are integral membrane proteins and that their mobility is controlled by the fluidity of the RER membrane. Examination of the hydrophobic interior of microsomal membranes by the freeze-fracture technique revealed the presence of homogeneously distributed 105-A intramembrane particles in control rough microsomes. However, aggregation of ribosomes by RNase, or their removal by treatment with puromycin, led to a redistribution of the particles into large aggregates on the cytoplasmic fracture face, leaving large particle-free regions.

scholarly journals CHANGES IN THE RIBOSOME CONTENT, PRINCIPAL MICROSOMAL PROTEIN COMPOSITION, AND SECRETORY CHARACTER OF MAMMARY EPITHELIAL ROUGH ENDOPLASMIC RETICULUM DURING DIFFERENTIATION

1974 ◽  
Vol 61 (3) ◽  
pp. 613-632 ◽  
Author(s):  
Frank Slaby ◽  
Carolyn Brown
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Protein Composition ◽  
Mammary Development ◽  
Mammary Epithelial ◽  
Density Range ◽  
Short Period ◽  
Rough Er

The equilibrium density distribution, protein composition, and secretory character of mouse mammary epithelial rough microsomes have been determined during differentiation. The density range exhibited by the rough microsomes broadens during mammary development; rough microsomes within the 1.25–1.29 g/ml density range appear soon after conception and then within the 1.30–1.34 range after the onset of lactation. The appearance of these denser microsomes represents the progressive increase of the average ribosome content of the rough endoplasmic reticulum (ER) during gestation and lactation. Fractionation of rough microsomal proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals that two proteins, having molecular weights of 57,000 and 76,000, occur to a significant extent only during lactation and are then most prominent in the very dense rough microsomes of the 1.30–1.34 range. Nascent polypeptide chains discharged (by incubation with puromycin) from 17-days lactation rough microsomes in either the 1.21–1.29 or 1.30–1.34 density range are distributed equally between the intra- and extravesicular compartments. Whereas 36% of the chains are discharged intravesicularly from 1-day lactation rough microsomes in the 1.30–1.34 range, only 25% are so discharged from those in the 1.21–1.29 range. The results indicate (a) that there is no correlation between the relative levels in lactation rough microsomes of the two microsomal proteins which become prominent during lactation and the extent of secretory activity and (b) that for a short period after parturition the rough ER elements bearing high surface densities of ribosomes have a greater proportion of ribosomes synthesizing milk proteins than the rough ER elements with moderate ribosome densities.

scholarly journals A comparative study of the molecular structures of the plasma membranes and the smooth and the rough endoplasmic-reticulum membranes from rat liver

1972 ◽  
Vol 129 (3) ◽  
pp. 781-788 ◽  
Author(s):  
F. Morin ◽  
S. Tay ◽  
H. Simpkins
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Rat Liver ◽  
Rough Endoplasmic Reticulum ◽  
Plasma Membranes ◽  
Structural Changes ◽  
Molecular Structures ◽  
Endoplasmic Reticulum Membrane ◽  
Marker Enzyme ◽  
Membrane Phospholipids

Plasma-membrane as well as smooth-, rough- and degranulated-endoplasmic-reticulum-membrane fractions were isolated from the microsomal pellet of rat liver. The purity of these fractions, as determined by marker-enzyme activities, electron microscopy, cholesterol content and RNA content, was found to be adequate for a comparative structural study. Major differences in lipid and protein composition were found to exist between the plasma membrane and the endoplasmic reticulum, but not between the smooth and the rough fractions of the endoplasmic reticulum. Differences in the location of membrane protein thiol groups and the mobility of the membrane phospholipids were observed between the plasma membranes and the endoplasmic reticulum, and these could be explained by differences in protein and lipid composition. However, by employing fluorescence and spin-labelling techniques structural changes were also observed between the smooth and the rough endoplasmic-reticulum fractions. These results suggest that the structural heterogeneity existing between the two latter membrane fractions occurs near or on their membrane surfaces and is not due to the greater number of ribosomes bound to the rough endoplasmic-reticulum fraction.

Modification of Pineal Ultrastructure by Exogenous Hormones

1967 ◽  
Vol 25 ◽  
pp. 170-171
Author(s):  
R. A. Turner ◽  
A. E. Rodin ◽  
D. K. Roberts
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Estradiol Benzoate ◽  
Female Rats ◽  
List Type ◽  
Type Number ◽  
Pregnant Rats ◽  
Gonadal Atrophy ◽  
Pineal Ultrastructure

There have been many reports which establish a relationship between the pineal and sexual structures, including gonadal hypertrophy after pinealectomy, and gonadal atrophy after injection of pineal homogenates or of melatonin. In order to further delineate this relationship the pineals from 5 groups of female rats were studied by electron microscopy:ControlsPregnant ratsAfter 4 weekly injections of 0.1 mg. estradiol benzoate.After 8 daily injections of 150 mcgm. melatonin (pineal hormone).After 8 daily injections of 3 mg. serotonin (melatonin precursor).No ultrastructural differences were evident between the control, and the pregnancy and melatonin groups. However, the estradiol injected animals exhibited a marked increase in the amount and size of rough endoplasmic reticulum within the pineal cells.

Membrane-associated microtubular areays induced in proximal myelinated processes of dorsal root ganglia by large doses of vitamin B6

1986 ◽  
Vol 44 ◽  
pp. 368-369
Author(s):  
V.J. Montpetit ◽  
S. Dancea ◽  
L. Tryphonas ◽  
D.F. Clapin
Keyword(s):  
Animal Model ◽  
Endoplasmic Reticulum ◽  
Dorsal Root Ganglia ◽  
Rough Endoplasmic Reticulum ◽  
Dorsal Root ◽  
Vitamin B6 ◽  
Morphological Changes ◽  
Model System ◽  
Sensory Nerves ◽  
Peripheral Sensory

Very large doses of pyridoxine (vitamin B6) are neurotoxic in humans, selectively affecting the peripheral sensory nerves. We have undertaken a study of the morphological and biochemical aspects of pyridoxine neurotoxicity in an animal model system. Early morphological changes in dorsal root ganglia (DRG) associated with pyridoxine megadoses include proliferation of neurofilaments, ribosomes, rough endoplasmic reticulum, and Golgi complexes. We present in this report evidence of the formation of unique aggregates of microtubules and membranes in the proximal processes of DRG which are induced by high levels of pyridoxine.

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