Reduction In Number Of Granules Research Articles

Homologs of PROTEIN TARGETING TO STARCH Control Starch Granule Initiation in Arabidopsis Leaves.

The molecular mechanism that initiates the synthesis of starch granules is poorly understood. Here, we discovered two plastidial proteins involved in granule initiation in Arabidopsis thaliana leaves. Both contain coiled coils and a family-48 carbohydrate binding module (CBM48) and are homologs of the PROTEIN TARGETING TO STARCH (PTST) protein; thus, we named them PTST2 and PTST3. Chloroplasts in mesophyll cells typically contain five to seven granules, but remarkably, most chloroplasts in ptst2 mutants contained zero or one large granule. Chloroplasts in ptst3 had a slight reduction in granule number compared with the wild type, while those of the ptst2 ptst3 double mutant contained even fewer granules than ptst2 The ptst2 granules were larger but similar in morphology to wild-type granules, but those of the double mutant had an aberrant morphology. Immunoprecipitation showed that PTST2 interacts with STARCH SYNTHASE4 (SS4), which influences granule initiation and morphology. Overexpression of PTST2 resulted in chloroplasts containing many small granules, an effect that was dependent on the presence of SS4. Furthermore, isothermal titration calorimetry revealed that the CBM48 domain of PTST2, which is essential for its function, interacts with long maltooligosaccharides. We propose that PTST2 and PTST3 are critical during granule initiation, as they bind and deliver suitable maltooligosaccharide primers to SS4.

Serotonin-producing enterochromaffin (EC) cells of gastrointestinal mucosa in dexamethasone-treated rats

The aim of our study was to investigate the morphological, immunohistochemical and ultrastructural changes of rat serotonin-producing enterochromaffin (EC) cells of gastrointestinal mucosa in dexamethasone-treated rats (D). After 12-daily intraperitoneal administration of 2 mg/kg dexamethasone, rats developed diabetes similar to human diabetes type 2. Stomach, small and large intestines were examined. Large serotonin positive EC cells appeared in the corpus mucosa epithelium of D group of rats, although these cells were not present in control (C) rats. Both volume fraction and the number of EC cells per mm 2 of mucosa were significantly increased only in the duodenum. However, the number of EC cells per circular sections of both antrum and small intestine was increased, but reduced both in the ascending and descending colon in D group. The dexamethasone treatment caused a strong reduction in number of granules in the antral EC cells, while it was gradually increased beginning from the jejunum to descending colon. The mean granular content was reduced in the antral EC cells but increased in the jejunal EC cells in D group. In conclusion, the present study showed that morphological changes in gut serotonin-producing EC cells occurred in diabetic rats.

Cell surface dynamics of neutrophils stimulated with phorbol esters or retinoids.

Neutrophils undergo rapid morphological changes as well as metabolic perturbations when stimulated with certain phorbol esters. Stimulated cells initially exhibit pronounced projections emanating from the cell bodies, followed by rounding of the cells, reduction in granule number, and the appearance of intracellular vesicles. We show these vesicles to be derived, at least in part, from the plasmalemma. The experimental approach involved labeling stimulated and unstimulated cells with native ferritin and cationized ferritin, along with the cytochemical localization of ecto-5'-nucleotidase. The labeling patterns of the vesicles indicate that these structures are involved in both phorbol ester-stimulated adsorptive and fluid-phase endocytosis. Neutrophils stimulated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) exhibit two distinct rates of superoxide release in which the second, prolonged level is approximately 50% of the initial rate. All-trans-retinal, which we have recently shown to stimulate O2- release but not granule exocytosis or cell vesiculation, induces a single prolonged rate of maximal O2- release. Neutrophils treated with both all-trans-retinal and TPA exhibit only a single sustained rate of maximal O2- release similar to that observed with all-trans-retinal alone. Moreover, treatment of cells with all-trans-retinal blocks the vesiculation of neutrophils induced by TPA in a dose-dependent manner. This observation provides a possible explanation for the differences in the kinetics of superoxide release.

Zymogen granules of pancreas decrease in size in response to feeding.

In the first descriptions of pancreatic enzyme secretion about 100 years ago, it was noticed that zymogen granules became smaller and disappeared from the apical region of acinar cells after feeding. We have repeated these experiments and characterized changes in granule size by quantitative electron microscopy 90 min after feeding previously fasted rats. In fasted animals, granules occupied the apical portion of the cell, had an average number of 45 +/- 3 granules per cell section (+/- SE), and measured 0.85 +/- 0.15 micrometers in diameter (+/- SD). After feeding, the number and size of granules decreased. Individual samples showed either a decrease in size alone or a decrease in both size and number, but in no case did they show a reduction in granule number alone. The mean diameter of granules decreased to 0.65+/- 0.15 microns (+/- SD) or about a 55% reduction in average granules volume as compared to controls (0.32 vs. 0.14 microns 3). The size distributions were unimodal and normal in both fasted and fed rats; however, in fed animals, the distribution was shifted to lower values (diameter range 0.40-1.40 microns for fasted rats vs. 0.10-1.30 microns for fed rats). The number of granules decreased to an average of 29 +/- 2 granules per cell section (+/- SE) after feeding, and, on the average, samples with the most granules had larger ones than samples with the fewest granules. The present results support the original observations on live rabbit pancreas that individual granules decrease in size in response to feeding. We suggest that these size changes reflect the loss of proteins across the granule membrane as proposed by the equilibrium hypothesis for digestive enzyme secretion.

Release of calcitonin from thyroid granules.

THYROID parafollicular cells contain calcitonin in a granular form. Reduction in numbers of granules and vesicles occurs during induced calcitonin secretion in vivo1, and from thyroid slices2. Particulate fractions with the biological activity of calcitonin have been derived from homogenates of pig, calf and rat thyroid glands3,4. We have prepared calcitonin containing particulate fractions from pig thyroid and have studied the properties of the isolated granules.

Granulated vesicles in sympathetic nerve endings in the pineal gland: observations on the effects of pharmacologic agents by electron microscopy.

AbstractThe effects of pharmacologic agents upon granulated vesicles in the sympathetic nerve endings of the pineal gland were studied electron microscopically. The most common granulated vesicle measures 400 Å and has an eccentric granule (Type IA); a few vesicles are as large as 1000 Å (Type IB). The vesicles also contain fine grains which may be the subunits of which the granules are composed. Reserpine causes many vesicles to become elliptical, raising the possibility of an effect upon the vesicle membrane. Depletion of granules by reserpine is confirmed and fine grains are also depleted. p‐Chlorphenylalanine, which reduces serotonin concentration, causes a reduction in number of granules but leaves fine grains. p‐Chlorphenylalanine followed by pargyline, induces a reduction in number of granules but a considerable number are present suggesting persistence or re‐accumulation of norepinephrine or other catecholamines. Oxypertine and desmethylimipramine (DMI) deplete granulated vesicles but fine grains remain. Another kind of granulated vesicle has a different ultrastructure than the Type IA and IB and measures 1000 Å (Type II). This kind of granulated vesicle is not depleted by reserpine, p‐chlorphenylalanine, oxypertine or desmethylimipramine suggesting that it contains neither catecholamines nor serotonin.

THE EFFECTS OF RESERPINE AND HYPOXIA ON THE AMINE-STORING GRANULES OF THE HAMSTER CAROTID BODY

The carotid bodies from control, reserpine-treated, and hypoxia-treated hamsters were fixed with phosphate-buffered glutaraldehyde and osmium tetroxide, s-Collidine-buffered osmium tetroxide, or phosphate-buffered glutaraldehyde followed by potassium dichromate incubation. Following glutaraldehyde-osmium tetroxide fixation no differences in density or population of the electron-opaque granules in the glomus cells of either control or experimental animals were observed. With s-Collidine-buffered osmium tetroxide and the glutaraldehyde-dichromate technique a marked decrease in density without an appreciable reduction in number of granules was noted after reserpine treatment, while in hypoxia-treated hamsters the density and population of the granules were not different from those of the controls. The results indicate that reserpine depletes the amines without granule disappearance and that hypoxia does not affect the amine content of the granules. It is suggested that following glutaraldehyde-osmium tetroxide double fixation, persistence of the density of the granules in reserpine-treated animals is due primarily to the nonamine content, and that the amines in the glomus cells are probably not directly involved in the respiratory reflex.