scholarly journals BETA GRANULE FORMATION IN ISOLATED ISLETS OF LANGERHANS

1969 ◽  
Vol 42 (3) ◽  
pp. 695-705 ◽  
Author(s):  
S. L. Howell ◽  
M. Kostianovsky ◽  
P. E. Lacy
Keyword(s):  
Amino Acids ◽  
Endoplasmic Reticulum ◽  
Islets Of Langerhans ◽  
Golgi Complex ◽  
Secretory Granules ◽  
Isolated Islets ◽  
Granule Formation ◽  
Intact Cells ◽  
Rat Islets Of Langerhans ◽  
Electron Lucent

The distribution of radioautographic grains over organelles within the beta cells of rat islets of Langerhans was investigated at various times after pulse labeling of the isolated islets with tritium-labeled amino acids. Ten minutes after the start of labeling most of the grains were situated over the endoplasmic reticulum and cytoplasm; by contrast, 60 min from the start of labeling the majority of the grains were associated with the beta granules. At 20, 30, and 45 minutes after pulse labeling the proportion of grains associated with the Golgi complex was increased two- to three-fold over the 10- or 60-minute values. The distribution of radioautographic grains over granules in the intact cells did not suggest that the electron-lucent type of secretory granules were precursors of the electron-opaque granules. Furthermore, studies of the pattern of grains over granules isolated by centrifugation 60 min after pulse labeling showed no preferential labeling of the electron-lucent type of granule. It is concluded that labeled amino acids are incorporated initially in the endoplasmic reticulum, and that the label subsequently appears in the beta granules. The Golgi complex participates either in the formation of the beta granule or in the translocation of the granule through the cytoplasm of the cell.

scholarly journals ISOLATION AND PROPERTIES OF SECRETORY GRANULES FROM RAT ISLETS OF LANGERHANS

1969 ◽  
Vol 41 (1) ◽  
pp. 162-166 ◽  
Author(s):  
Marie H. Greider ◽  
S. L. Howell ◽  
P. E. Lacy
Keyword(s):  
Surface Structure ◽  
Islets Of Langerhans ◽  
Thin Section ◽  
Phosphotungstic Acid ◽  
Secretory Granules ◽  
Crystalline Material ◽  
Intact Cells ◽  
Rat Islets ◽  
Rat Islets Of Langerhans

Beta granules isolated from rat islets of Langerhans and subjected only to phosphotungstic acid had, in negatively stained images, a 50-A periodicity. This periodicity was also observed in thin-section profiles of beta granules in intact cells. In shadowed preparations, the granules were spherical in shape and had irregular edges and surface structure. The presence of such a periodicity in the beta granule indicates that its matrix may be composed of a crystalline material.

A Study of Granule Formation in the Bat Parafollicular Cell

1969 ◽  
Vol 5 (2) ◽  
pp. 531-559
Author(s):  
E. A. NUNEZ ◽  
R. P. GOULD ◽  
S. J. HOLT
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Complex ◽  
Secretory Granules ◽  
Granular Endoplasmic Reticulum ◽  
Secretory Product ◽  
Central Mass ◽  
Granule Formation ◽  
Cytoplasmic Matrix ◽  
Parafollicular Cell ◽  
Parafollicular Cells

The fine structure of the bat thyroid parafollicular cell has been examined at monthly intervals throughout the hibernating period. During November and December parafollicular cells appear either partly or totally degranulated and intact dense secretory granules are relatively sparse. The degranulated cells exhibit an inconspicuous Golgi complex and relatively few lysosome-type bodies. Few degranulated parafollicular cells are present in thyroid glands from bats collected in January. When found they are characterized by the presence of whorls of cytoplasmic agranular membranes which enclose a central mass of cellular debris. January bat thyroids are characterized by the presence of three different types of parafollicular cell. One type contains no secretory granules. The cytoplasmic matrix of this type is rich in granular endoplasmic reticulum and free ribosomes and its small Golgi complex consists of several slightly dilated saccules. In close proximity to the Golgi complex are numerous small to medium-sized vesicles which often appear to merge with Golgi elements. Such vesicles are considered to represent the vehicle by which secretory product is transferred from the endoplasmic reticulum to the Golgi complex. The second type of parafollicular cell differs from the first in containing large numbers of intact dense secretory granules. It is also characterized by an extensive Golgi complex which appears to be forming new secretory granules, and by a less extensive granular endoplasmic reticulum. The third type of parafollicular cell shows a structure intermediate between the first two. The cytoplasm of all three types of January parafollicular cells contains many structures belonging to the lysosomal-vacuolar system, including autophagic vacuoles, vacuolated dense bodies and multivesicular bodies. By February and March only parafollicular cells of type 2 are observed. They contain few lysosome-like structures. It is concluded that during mid-hibernation (January), parafollicular cells undergo a series of intracellular changes during which new dense secretory granules are produced. Accompanying granule formation is an augmentation of lysosome-like structures which probably serve as a means of digesting debris from previous secretory cycles.

Calcium distribution in islets of Langerhans: a study of calcium concentrations and of calcium accumulation in B cell organelles

1975 ◽  
Vol 19 (2) ◽  
pp. 395-409
Author(s):  
S.L. Howell ◽  
W. Montague ◽  
M. Tyhurst
Keyword(s):  
Endoplasmic Reticulum ◽  
Cyclic Amp ◽  
B Cell ◽  
Islets Of Langerhans ◽  
Cyclic Gmp ◽  
Cell Organelles ◽  
Calcium Accumulation ◽  
Labile Pool ◽  
Storage Granules ◽  
Rat Islets Of Langerhans

Calcium concentrations of various pancreatic B cell organelles have been determined by X-ray microanalysis of areas of frozen sections of unfixed rat islets of Langerhans. Highest concentrations were detected in storage granules and in mitochondria, although calcium was also present in nuclei, in areas of endoplasmic reticulum and of cytoplasm. Accumulation of 45Ca by isolated organelles has been studied in homogenates and isolated subcellular fractions of rat islets of Langerhans. In the presence of a permeant anion (oxalate or phosphate), accumulation of 45Ca into mitochondria and microsomes was strongly stimulated by ATP. This net uptake was diminished during incubation of homogenates or of a mitochondria plus storage granule-rich fraction in the presence of cyclic AMP, dibutyryl cyclic GMP; 2:4-dinitrophenol or of ruthenium red. Investigations of the characteristics of 45Ca accumulation by homogenates prepared from storage granule-depleted islets showed no differences from those of normal islets, suggesting that the granules do not represent an important labile pool of calcium. With the exception of cyclic AMP and cyclic GMP none of the insulin secretagogues tested (glucose, leucine, arginine, adrenalin, noradrenalin, theophylline, glibenclamide) altered calcium accumulation by islet homogenates. On the basis of absolute calcium levels and of 45Ca uptake studies it is concluded that islet B cells contain a readily exchangeable mitochondrial calcium pool, and an endoplasmic reticulum pool containing a lower concentration of calcium which is also readily exchangeable. The storage granules, despite their high calcium content, do not appear to constitute a labile pool. It seems likely that the labile mitochondria and endoplasmic reticulum pools play a predominant role in the regulation of cytoplasmic free calcium levels, which may in turn be important in the regulation of rates of insulin secretion.

scholarly journals ISOLATION AND PROPERTIES OF SECRETORY GRANULES FROM RAT ISLETS OF LANGERHANS

1969 ◽  
Vol 41 (1) ◽  
pp. 167-176 ◽  
Author(s):  
S. L. Howell ◽  
D. A. Young ◽  
P. E. Lacy
Keyword(s):  
Islets Of Langerhans ◽  
Secretory Granules ◽  
Sodium Deoxycholate ◽  
Rat Islets ◽  
The Matrix ◽  
Effects Of Ph ◽  
The Stability ◽  
Rat Islets Of Langerhans ◽  
Specific Insulin

A partially purified secretory granule fraction, isolated from rat islets of Langerhans by differential centrifugation, was used for investigating the stability of the beta granules during incubation in various conditions. Effects of pH, temperature, and time were studied; the granules possessed optimal stability at 4° and pH 6.0, and could be solubilized at pH 4.0 or 8.5, or in the presence of sodium deoxycholate, but not by phospholipase c, ouabain, or alloxan. Incubation with glucose or some of its metabolites, or with tolbutamide, ATP, or cyclic 3',5'-AMP did not alter the stability of the beta granules Exogenous insulin-131I was not bound by the isolated granules under the conditions used; no specific insulin-degrading activity could be detected in subcellular fractions of the islets. These findings indicate that intracellular solubilization of the granules with subsequent diffusion of the insulin into the extracellular space is not a likely mode of insulin secretion in vivo, and suggest that a crystalline zinc-insulin complex may exist in the matrix of the beta granules.

scholarly journals The human Myt1 kinase preferentially phosphorylates Cdc2 on threonine 14 and localizes to the endoplasmic reticulum and Golgi complex.

1997 ◽  
Vol 17 (2) ◽  
pp. 571-583 ◽  
Author(s):  
F Liu ◽  
J J Stanton ◽  
Z Wu ◽  
H Piwnica-Worms
Keyword(s):  
Amino Acids ◽  
Endoplasmic Reticulum ◽  
Golgi Complex ◽  
Catalytic Domain ◽  
Cyclin B ◽  
Dependent Manner ◽  
Cdc2 Kinase ◽  
Dual Specificity ◽  
Catalytically Active ◽  
Specificity Protein

Entry into mitosis requires the activity of the Cdc2 kinase. Cdc2 associates with the B-type cyclins, and the Cdc2-cyclin B heterodimer is in turn regulated by phosphorylation. Phosphorylation of threonine 161 is required for the Cdc2-cyclin B complex to be catalytically active, whereas phosphorylation of threonine 14 and tyrosine 15 is inhibitory. Human kinases that catalyze the phosphorylation of threonine 161 and tyrosine 15 have been identified. Here we report the isolation of a novel human cDNA encoding a dual-specificity protein kinase (designated Myt1Hu) that preferentially phosphorylates Cdc2 on threonine 14 in a cyclin-dependent manner. Myt1Hu is 46% identical to Myt1Xe, a kinase recently characterized from Xenopus laevis. Myt1Hu localizes to the endoplasmic reticulum and Golgi complex in HeLa cells. A stretch of hydrophobic and uncharged amino acids located outside the catalytic domain of Myt1Hu is the likely membrane-targeting domain, as its deletion results in the localization of Myt1Hu primarily to the nucleus.

Modifications of pars intermedia cells of ovariectomized rats by oestrogen and progesterone

1986 ◽  
Vol 111 (1) ◽  
pp. 17-24 ◽  
Author(s):  
Adriana Beatriz Ferreira ◽  
Maria Ester Celis
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Secretory Granules ◽  
Secretory Activity ◽  
Ovariectomized Rats ◽  
Ultrastructural Changes ◽  
Synthetic Activity ◽  
Pars Intermedia ◽  
Cytological Features ◽  
Electron Lucent

Abstract. The effects of the ovarian steroids, oestradiol benzoate (EB), and progesterone (P) on the cells of pars intermedia (PI) from chronically ovariectomized rats (CHR-OVX) were analyzed by qualitative and quantitative electron microscopy (EM) at different intervals after steroid injection. The PI cells of CHR-OVX are rich in secretory granules but poor in organelles related to hormonal synthesis. Twenty-four h after EB administration the cells exhibited cytological features indicative of an increased synthetic activity. These included hypertrophy of rough endoplasmic reticulum, cisternae, a moderately developed Golgi complex, and newly formed granules. These features were also observed in PI cells 48 h after EB administration. Thirty-two and 56 h after the treatment, the PI cells showed signs of both increased synthetic and secretory activity. Thus, it was possible to observe a well-developed rough endoplasmic reticulum, and Golgi apparatus, numerous electron-lucent vesicles, and secretory granules in contact with the cell membrane. However, no exocytotic figures were observed. Progesterone administration resulted in considerable modifications of the ultrastructural features of PI cells also indicative of increased synthetic and secretory activity. The greatest modifications were observed in the mornings with changes that were 12 h out of phase with respect to those observed with EB. Quantitative estimations of the variation in the content of secretory granules of PI cells fully confirmed the qualitative observations described above. The serum α-MSH concentrations in ovariectomized rats was found to be incresed 24 h after administration of a single dose of EB and thereafter serum MSH exhibited high levels in the afternoon, whereas the values in the morming were lower. In spayed rats, progesterone injection also resulted in an increase of the serum MSH concentration, but with high levels in the mornings and low levels in the afternoons. In conclusion, EB and P induce modifications in the levels of α-MSH as well as in the ultrastructural changes of the PI cells.

scholarly journals ISOLATION AND PROPERTIES OF SECRETORY GRANULES FROM RAT ISLETS OF LANGERHANS

1969 ◽  
Vol 41 (1) ◽  
pp. 154-161 ◽  
Author(s):  
S. L. Howell ◽  
C. J. Fink ◽  
P. E. Lacy
Keyword(s):  
Islets Of Langerhans ◽  
Secretory Granule ◽  
Islet Cells ◽  
Secretory Granules ◽  
Morphological Characterization ◽  
Differential Centrifugation ◽  
Rat Islets ◽  
Granule Fraction ◽  
Final Yield ◽  
Rat Islets Of Langerhans

A method has been devised for the isolation of a secretory granule fraction from isolated rat islets of Langerhans. The islets were homogenized in buffered sucrose, and the homogenate was separated into nuclear, mitochondrial, secretory granule, and microsomal fractions by differential centrifugation. The secretory granule fraction was purified by differential centrifugation in discontinuous sucrose density gradients. A greater degree of purification could be achieved by the use of two successive gradients of this type, although the final yield was greatly reduced. Biochemical and morphological characterization of the fractions was obtained; the secretory granule fraction contained both insulin and glucagon. The limiting membranes of the granules remained intact and the general appearance of the granules was similar to that seen within the whole islet cells.

scholarly journals Small disulfide loops in peptide hormones mediate self-aggregation and secretory granule sorting

2021 ◽  
Author(s):  
Jennifer Reck ◽  
Nicole Beuret ◽  
Erhan Demirci ◽  
Cristina Prescianotto-Baschong ◽  
Martin Spiess
Keyword(s):  
Endoplasmic Reticulum ◽  
Secretory Granule ◽  
Secretory Granules ◽  
Peptide Hormones ◽  
Secreted Proteins ◽  
Reporter Protein ◽  
Granule Formation ◽  
Functional Amyloids ◽  
Golgi Network ◽  
Self Aggregation

ABSTRACTUnlike constitutively secreted proteins, peptide hormones are stored in densely packed secretory granules, before regulated release upon stimulation. Secretory granules are formed at the trans-Golgi network (TGN) by self-aggregation of prohormones as functional amyloids. The nonapeptide hormone vasopressin, which forms a small disulfide loop, was shown to be responsible for granule formation of its precursor in the TGN as well as for toxic fibrillar aggregation of unfolded mutants in the endoplasmic reticulum (ER). Several other hormone precursors also contain similar small disulfide loops suggesting their function as a general device to mediate aggregation for granule biogenesis. To test this hypothesis, we studied the capacity of small disulfide loops of different hormone precursors to mediate aggregation in the ER and the TGN. They indeed induced ER aggregation although to different extents in Neuro-2a and COS-1 cells. Fused to a constitutively secreted reporter protein, they also promoted sorting into secretory granules, enhanced stimulated secretion, and increased Lubrol insolubility in AtT20 cells. These results support the hypothesis that small disulfide loops act as novel signals for secretory granule biogenesis and sorting by self-aggregation.

Studies on the Effects of Growth Hormone and Thyroxine on Proinsulin Synthesis and Insulin Formation in the Isolated Islets of Langerhans of the Rat

1972 ◽  
Vol 50 (12) ◽  
pp. 1147-1151 ◽  
Author(s):  
A. M. Sun ◽  
B. J. Lin ◽  
R. E. Haist
Keyword(s):  
Growth Hormone ◽  
Islets Of Langerhans ◽  
Golgi Complex ◽  
Incubation Medium ◽  
Microsomal Fraction ◽  
Isolated Islets ◽  
Incubation Mixture ◽  
Insulin Biosynthesis ◽  
Isolated Islets Of Langerhans ◽  
Proinsulin Synthesis

By using pulse-chase and islet-fractionating techniques, proinsulin synthesis and insulin formation in isolated islets from normal and hypophysectomized (Hx) rats have been studied. In both groups of rat islets, proinsulin synthesis took place in the microsomal fraction and its conversion to insulin in the granular fraction (which includes the Golgi complex). The total incorporation of 3H-leucine into proinsulin and insulin in the islets from Hx rats during the 30 min period of pulsing was 48% of the value obtained in the normal islets from control rats. When growth hormone (GH) was added to the incubation medium for islets from Hx rats, a substantial increase (79% of that found in normal islets) in total incorporation of 3H-leucine into proinsulin and insulin was observed. When the incubation mixture was supplemented with thyroxine (THY) along with growth hormone, the conversion of proinsulin to insulin was increased during the pulsing and chasing periods. The enhancement of insulin biosynthesis as a result of both GH and THY was confirmed by straight pulsing experiments. The possible mechanisms for the enhanced effect are discussed.

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