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PubMed1988

Subcellular compartmentalization by local differentiation of cytoplasmic structure.

The compartmentalization of eukaryotic cells by internal membranes and the subcellular localization of endogenous macromolecules by specific binding mechanisms are familiar concepts. In this report we present evidence that the cytoplasmic ground substance, which surrounds and contains the membrane-bound compartments, may also be compartmentalized by local differentiations of its submicroscopic structure that sort subcellular particles on the basis of size. The subcellular distribution of size-fractionated, fluorescent tracer particles was studied in living cells by ratio imaging and fluorescence recovery after photobleaching (FRAP). Large and small particles showed different distributions within the cytoplasmic volume, suggesting that the large particles were relatively excluded from some domains. While the structural basis for this phenomenon is not yet understood in detail, ratio imaging of large and small particles can be used as an empirical tool to identify cytoplasmic compartments for further study. The cytoplasmic diffusion coefficient (Dcyto) and % mobile fraction of the large particles showed considerable spatial variation over the projected area of the cell, while Dcyto and % mobile fraction of the small particles did not. A model is presented to account for this difference. Based on this model, a method is proposed by which FRAP can be used to detect sol-gel transitions in the cytoplasmic ground substance of living cells.

Animals↗
PubMed1995

Developing mossy fiber terminal fields in the rat cerebellar cortex may segregate because of Purkinje cell compartmentation and not competition.

Many mossy fiber afferent projections to the rat cerebellar cortex terminate in parasagittal bands. In particular, the anterior lobe vermis of the cerebellum contains alternating bands of mossy fibers from the spinal cord and external cuneate nuclei. The cerebellar cortical efferents, the Purkinje cells, are also organized in parasagittal bands. These can be revealed by immunochemical staining for the antigen zebrin II, which is selectively expressed by bands of Purkinje cells. In some cases, the boundaries between mossy fiber terminal fields align with identified transitions between zebrin+/- sets of Purkinje cells, whereas others are located within apparently homogeneous Purkinje cell compartments. Two theories can explain the terminal-field topography: In one view, mossy fiber terminals segregate during development, because growth cones from different sources compete for common territory. Alternatively, mossy fiber growth cones directly recognize chemically distinct target territories, and activity-dependent mechanisms play only minor roles. To explore these issues, two sets of experiments were performed. First, the terminal-field map of the neonatal spinocerebellar projection was compared to the Purkinje cell compartmentation as revealed by anticalbindin immunocytochemistry. Second, subsets of spinocerebellar mossy fiber afferents were ablated early in postnatal development, and the consequences for the neighboring cuneocerebellar terminal fields were mapped in the adult with reference to the zebrin II+/- compartments. These experiments revealed no evidence that competitive interactions constrain the mossy fiber terminal-field distribution but, rather, suggest that the organization of the mossy fiber projections follows the compartmentation of the Purkinje cells.

Analysis of Variance↗
PubMed1990

Changes in calmodulin compartmentalization throughout capacitation and acrosome reaction in guinea pig spermatozoa.

Calmodulin has been postulated as a mediator in the calcium-dependent processes that culminate in the acrosome reaction. Changes in calmodulin compartmentalization as a consequence of the increased permeability to extracellular calcium during capacitation and acrosome reaction have been suggested. In the present study the temporal localization of calmodulin in guinea pig spermatozoa was studied during in vitro capacitation and acrosome reaction by indirect immunofluorescence. Capacitation was achieved by incubation in Tyrode medium supplemented with pyruvate, lactate, and glucose in the presence and in the absence of calcium. Acrosome reaction was elicited in three different conditions: 1) by transfer to minimal culture medium containing pyruvate and lactate (MCM-PL) after in vitro capacitation 2) by 0.003% Triton-X 100 treatment, and 3) by A 23187 addition to sperm samples incubated in MCM-PL. During capacitation, calmodulin was observed both in the acrosome and in the flagellum; this localization seemed to be independent of the presence of extracellular calcium and of exogenous substrates. Throughout the acrosome reaction, different stages of calmodulin compartmentalization were observed. It became clustered around the equatorial region just before or a little after the acrosome reaction had occurred. Later, it was observed around the postacrosomal region in the acrosome-reacted sperm. The changes in calmodulin distribution were found to be dependent on the stage in the acrosome reaction.

Acrosome↗
PubMed1997

N-cadherin-catenin interaction: necessary component of cardiac cell compartmentalization during early vertebrate heart development.

During early heart development the expression pattern of N-cadherin, a calcium-dependent cell adhesion molecule, suggests its involvement in morphoregulation and the stabilization of cardiomyocyte differentiation. N-cadherin's adhesive activity is dependent upon its interaction with the intracellular catenins. An association with alpha-catenin and beta-catenin also is believed to be involved in cell signaling. This study details the expression patterns of alpha-catenin, beta-catenin, and gamma-catenin, during definition of the cardiac cell population as distinct compartments in the anterior regions of the chick embryo between stages 5 and 9. The restriction of N-cadherin/catenin localization at stage 5+ from a uniform pattern in vivo, to specific cell clusters that demarcate areas where mesoderm separation is initiated, suggests that the N-cadherin/catenin complex is involved in boundary formation and in the subsequent cell sorting. The latter two processes lead to the specification and formation of the somatic and cardiac splanchnic mesoderm. N-cadherin colocalized with alpha- and beta-catenin at the cell membrane before and during the time that its expression becomes restricted to the lateral mesoderm and continues cephalocaudad into stage 8. These proteins continue to colocalize in the myocardium of the tubular heart. Plakoglobin is not expressed in this region during stages 6-8, but is detected in the myocardium later at stage 13. The observed in vivo expression patterns of alpha-catenin, beta-catenin, and plakoglobin suggest that these proteins are directly linked with the developmental regulation of cell junctions, as cardiac cells become stably committed and phenotypically differentiated to eventually form a mature myocardium. The localization of N-CAM also was analyzed during these stages to determine whether the N-cadherin-catenin localization was unique or whether other cell adhesion molecules were expressed similarly. The results indicate that the unique pattern of N-cadherin expression is not shared with N-CAM. We also show that perturbation of N-cadherin using a function perturbing N-cadherin antibody (NCD-2) inhibits normal early heart development and myogenesis in a cephalocaudad, stage-dependent manner. We propose a model whereby myocardial cell compartmentalization also defines the endocardial population. The presence of beta-catenin suggests that a similar signaling pathway involving Wnt (wingless)-mediated events may function in myocardial cell compartmentalization during early vertebrate heart development, as in Drosophila contractile vessel development.

Animals↗
PubMed1996

Intracellular compartmentalization of two differentially spliced s-rex/NSP mRNAs in neurons.

Using a subtractive hybridization technique directed to cloning transcripts with compartmentalized distributions within cerebral cortex neurons, we have isolated rat s-rex mRNAs that are analogues of the human neuroendocrine-specific NSP gene transcripts. Differential splicing produces two main s-rex mRNA that have different regional distributions in the developing and mature rat nervous system. In certain populations of adult brain neurons, most of s-rexs, mRNA and a substantial amount of s-rexb mRNA are localized to the axonal pole of the cell body. The localization of S-Rex/NSP proteins in these neurons suggests that s-rex mRNA compartmentalization targets the encoded proteins to specific regions of the neuron.

Alternative Splicing↗
PubMed1991

On the role of gravity and positional information in embryological axis formation and tissue compartmentalization.

The idea that gravity affects dorso-ventral polarization in anouran development contrasts with the theories of self-organization through reaction-diffusion processes. As a result of a literature study we discuss the role of gravity in embryological axis formation and speculate on an influence of gravity on tissue compartmentalization. The involvement of compartmentalization in tissue homeostasis is discussed in the light of the recent progress in mammalian cell culture studies.

Amphibians↗
PubMed1983

Molecular compartmentation by enzyme cluster formation. A view over current investigations.

Current investigations in different fields of cellular metabolism focus on the phenomenon of molecular compartmentation as an essential part of metabolic control. This type of compartment without surrounding membranes arises from enzyme cluster formation in the cell. The organization of the enzymes ranges from very loose, non-covalent aggregations, sometimes only transiently associated - dependent on metabolic or developmental state of the cell - to the very fixed, even covalently linked structures. These organized multienzyme systems produce a chemical microheterogeneity concerning the metabolite concentrations in the cell. Molecular compartmentation is the description of this chemical microheterogeneity in a biological term.

Animals↗
PubMed1991

Studies on the compartmentation of DOG metabolism in the brain.

Using 31P-NMR studies we have observed that 1. 2-Deoxyglucose leads into the brain in vivo and in superfused cortical slices in vitro to a maximum concentration at between 45 and 60 min, when 80% of the material is in the phosphorylated form. 2. The phosphorylated DOG6P disappears from the n.m.r. spectra with a half-life of ca 130 min. 3. Two resonances of DOG6P are observed in the actively metabolising tissue, whereas only one is visible in deproteinised tissue extracts. This suggests that the DOG6P is in two separate compartments which differ in pH. 4. Compartmentation between mitochondria, nerve endings and cytoplasm was concluded to be unlikely from subcellular fractionation studies, but the possibility of compartmentation between neurones and glia could not be so clearly assessed.

Animals↗
PubMed2006

Cellular and subcellular compartmentation of Ni in the Eurasian serpentine plants Alyssum bracteatum, Alyssum murale (Brassicaceae) and Cleome heratensis (Capparaceae).

This study investigated the cellular and subcellular compartmentation of Ni in the Eurasian serpentine species Alyssum murale, Alyssum bracteatum and Cleome heratensis and a non-serpentine population of A. murale (as a control) grown in hydroponic culture. Plant growth responses and Ni uptake clearly revealed the higher Ni tolerance of serpentine plants than the non-serpentine plants. Serpentine A. murale and A. bracteatum grew better at elevated (0.01 mM) Ni in the nutrient solution, supporting the view that the Ni hyperaccumulators have a higher requirement for Ni than normal plants. Low shoot Ni content of C. heratensis in response to the high Ni treatments indicated that this species employs an avoidance strategy for Ni tolerance. Energy-dispersive X-ray microanalysis showed that Ni was highly concentrated in the cell walls and cell lumen, most likely the vacuoles, of leaf epidermis of A. murale and A. bracteatum rather than in the mesophyll cells. EDX spectra from leaves of the non-serpentine A. murale suggested that Ni accumulated in both epidermal and mesophyll cells but not in the epidermal cell walls. Growth reduction and Ni toxicity in plants of the non-serpentine A. murale could be due to accumulation of Ni in the lumen of leaf mesophyll cells. Our data suggest that cellular and subcellular compartmentation are both possible mechanisms for Ni tolerance employed by the serpentine A. murale and A. bracteatum.

Brassicaceae↗
PubMed2000

Cellular compartmentation of cadmium and zinc in relation to other elements in the hyperaccumulator Arabidopsis halleri.

The cellular compartmentation of elements was analysed in the Zn hyperaccumulator Arabidopsis halleri (L.) O'Kane & Al-Shehbaz (=Cardaminopsis halleri) using energy-dispersive X-ray microanalysis of frozen-hydrated tissues. Quantitative data were obtained using oxygen as an internal standard in the analyses of vacuoles, whereas a peak/background ratio method was used for quantification of elements in pollen and dehydrated trichomes. Arabidopsis halleri was found to hyperaccumulate not only Zn but also Cd in the shoot biomass. While large concentrations of Zn and Cd were found in the leaves and roots, flowers contained very little. In roots grown hydroponically, Zn and Cd accumulated in the cell wall of the rhizodermis (root epidermis), mainly due to precipitation of Zn/Cd phosphates. In leaves, the trichomes had by far the largest concentrations of Zn and Cd. Inside the trichomes there was a striking sub-cellular compartmentation, with almost all the Zn and Cd being accumulated in a narrow ring in the trichome base. This distribution pattern was very different from that for Ca and P. The epidermal cells other than trichomes were very small and contained lower concentrations of Zn and Cd than mesophyll cells. In particular, the concentrations of Cd and Zn in the mesophyll cells increased markedly in response to increasing Zn and Cd concentrations in the nutrient solution. This indicates that the mesophyll cells in the leaves of A. halleri are the major storage site for Zn and Cd, and play an important role in their hyperaccumulation.

Arabidopsis↗
PubMed1983

Multiple forms of myeloperoxidase from human neutrophilic granulocytes: evidence for differences in compartmentalization, enzymatic activity, and subunit structure.

Multiple forms of myeloperoxidase from normal human neutrophilic granulocytes obtained from a single donor can be resolved by carboxymethyl (CM)-cellulose ion-exchange column chromatography into three forms (I, II, and III) designated in order of elution of adsorbed enzyme using a linear salt gradient. Selective solubilization of individual forms of the enzyme by detergent (form I) or high-ionic-strength procedures (forms II and III) suggested that these forms of the enzyme were compartmentalized differently. All three forms were purified by a combination of preferential extraction, manipulation of ionic strength, and ion-exchange and molecular sieve chromatography. Purified forms II and III had similar specific activities for a variety of substrates. Form I was less active toward several of these same substrates, most notably iodide, with a specific activity about one-half that of forms II and III. All forms had similar spectral properties characteristic of a type alpha heme. The amino acid compositions of the three forms were similar, yet significant differences were found in selected residues such as the charged amino acids. Native polyacrylamide gel electrophoresis resolved small differences in mobility between the forms which were consistent with the charge heterogeneity observed on CM-cellulose. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis data were consistent with the generally accepted subunit structure of two heavy chains and two light chains. All three forms contained a small-molecular-weight subunit of Mr 11,500. Form I contained a large subunit of Mr 63,000, while forms II and III contained a corresponding subunit of Mr approximately 57,500. We conclude that heterogeneity of human myeloperoxidase is accompanied by differences in cellular compartmentalization, enzymatic activity, and subunit structure.

Amino Acids↗
PubMed1979

Cable properties and compartmentation in Acetabularia.

The electrical cable properties of three different compartmentation types of Acetabularia cells have been investigated. These three types were: normal cells, 'stumps' (filled with cytoplasm, no central vacuole) and 'tubes' (cytoplasm depleted vacuoles). The latter two types have been obtained by centrifugation of normal cells. Qualitatively, the characteristic biphasic voltage response upon rectangular current pulses is the same in these three types. Quantitatively, however, the two conductances which can be obtained from the biphasic voltage response as well as the apparent capacity of several F . m-2 which derives from the large time constant of the second phase, are drastically increased in stumps and decreased in tubes compared to normal cells. The resting potential is a few mV more negative in stumps, and more positive in tubes, than in normal cells. Based on the existence of the high resting potential and the apparent large capacity in the non-vacuolated stumps, it is concluded that the electrogenic Cl- pump of Acetabularia is located in the plasmalemma membrane and that the apparent large capacity is not a result of the complicated membraneous organisation of the vacuolar system. Several possibilities are discussed, in relation to the quantitative correlation between intracellular compartmentation and electrical membrane parameters.

Acetabularia↗
PubMed1988

Compartmentalization of phospholipids for lipoprotein assembly on the basis of molecular species and biosynthetic origin.

Specific pools of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are compartmentalized on the basis of their biosynthetic origin for assembly into lipoproteins by rat hepatocytes in culture (Vance, J.E. and Vance, D.E. (1986) J. Biol. Chem. 261, 4486-4491). The present experiments confirm that PC and PE derived from serine, rather than from ethanolamine, are preferred for assembly into lipoproteins. One possible explanation for this compartmentalization is that defined molecular species of phospholipids are selected for secretion. Thus, the molecular species distribution of PC and PE of cultured rat hepatocytes incubated with one of [3H]choline, [3H]ethanolamine or [3H]serine was compared in the cells and in the lipoproteins secreted into the culture medium using high-performance liquid chromatography. The percent distribution of molecular species of PC and PE labeled from ethanolamine was the same in the cells and the medium. On the contrary, the percent distribution of molecular species of PC derived from [3H]choline, and PC and PE derived from [3H]serine, was different in the cells and secreted lipoproteins; the species 1-stearoyl-2-arachidonyl-PC and -PE were selectively not secreted. However, selection of defined molecular species of cellular PC labeled from serine would only account for the specific radioactivity of secreted PC labeled from serine being 46% higher than in the hepatocytes at 4 h, whereas the specific radioactivity of medium PC was actually 300% higher than in the cells. A comparison of the labeling pattern of molecular species of PC and PE using [3H]serine and [3H]ethanolamine as precursors suggests that PE methyltransferase may prefer certain species of PE as substrate if the PE was derived from either serine or ethanolamine.

Animals↗
PubMed1991

Compartmentation of intracellular folates. Failure to interconvert tetrahydrofolate cofactors to dihydrofolate in mitochondria of L1210 leukemia cells treated with trimetrexate.

Following exposure of L1210 leukemia cells to antifolates, tetrahydrofolate-dependent purine and pyrimidine biosyntheses are blocked despite the presence of the major portion of tetrahydrofolate cofactors. Previous studies from this laboratory demonstrated that this cannot be due to direct inhibition of thymidylate synthase by dihydrofolate polyglutamates or other endogenous folates and suggested that this phenomenon is due to compartmentation of tetrahydrofolate cofactors unavailable for interconversion and/or oxidation when dihydrofolate reductase activity is abolished by antifolates. The present paper evaluates the possibility that tetrahydrofolate cofactors in subcellular organelles, in particular, mitochondria, are unavailable for oxidation by thymidylate synthase. Particulate and cytosolic fractions were obtained from L1210 cells following homogenization and differential centrifugation. The crude mitochondrial fraction contained 20.1% of the total folate pool and included 5-formyltetrahydrofolate, 10-formyltetrahydrofolate and tetrahydrofolate in proportions similar to intact cells. The cytosolic fraction had an increased proportion of tetrahydrofolate and decreased proportions of 5-formyl- and 10-formyltetrahydrofolate relative to intact cells or the particulate fraction. Exposure of cells to 10 microM trimetrexate for 30 min produced approximately 45% interconversion of tetrahydrofolate cofactors to dihydrofolate in the cytosolic fraction, a level much greater than that observed in whole cell extracts (25-30%), but had no effect on folate pools in the crude mitochondrial fraction. These data indicate that subcellular compartmentation accounts, in part, for the failure to oxidize tetrahydrofolate cofactors to dihydrofolate in the presence of antifolate levels that abolish dihydrofolate reductase activity.

Animals↗
PubMed1991

Compartmentalized gene expression during sporulation in Bacillus subtilis.

Two important features of endospore development in Bacillus subtilis--the compartmentalization of mother cell gene expression and the coordination of mother cell gene expression with forespore development--are governed by the highly regulated expression of the sigK gene, which encodes the mother cell-specific RNA polymerase sigma factor sigma K. Compartmentalized expression of sigK is associated both with a chromosomal DNA rearrangement and with the restriction of sigK transcription to the mother cell. A third mode of sigK regulation, which occurs at the level of activation of the sigK gene product by proteolytic processing, serves to couple gene expression between the mother cell and forespore compartments of the developing sporangium.

Bacillus subtilis↗
PubMed1986

SRIF-sensitive compartmentalization of stored rGH is abolished by hypothyroidism.

Rat adenohypophyses lose immuno- and bioassayable growth hormone in hypothyroidism. We examined whether the somatotroph also loses mechanisms for intracellular hormone compartmentalization during hypothyroidism. A series of identical perifusions was performed using pituitary tissue from thyroidectomized rats before and after thyroxine replacement. Somatostatin (SRIF), (Bu)2cAMP and potassium ion were employed to produce a wide range of hormone release responses. Growth hormone synthesis diminished with hypothyroidism and increased with thyroid hormone replacement. Growth hormone release was therefore expressed as a percent of pituitary content to circumvent effects of variable content. Post-somatostatin rebound release was lost in hypothyroidism: it fell progressively after thyroidectomy (day 7 = 45% of control; day 14 = 11%; day 71 = 3%) and was restored by thyroxine replacement (day 2 = 24%; day 5 = 50%; day 9 = 102%). In conclusion, hypothyroid somatotrophs lose the ability to sequester stored hormone in a SRIF-sensitive compartment. Thyroxine replacement restores that capability. Thus, SRIF-sensitive rGH compartmentalization is thyroid hormone dependent.

Animals↗
PubMed1987

Studies on the regulation of enolases and compartmentation of cytosolic enzymes in Saccharomyces cerevisiae.

Three enolase isoenzymes can be distinguished after electrophoresis of yeast crude extracts. After adding glucose to derepressed cells, there was a coordinated increase in the activity of enolase I and decrease in enolase II activity. Enolase I was found to be repressed and enolase II simultaneously induced by glucose. The third enolase activity remained unchanged and was identified as that of a hybrid enzyme. Enolase catalyses the first common step of glycolysis and gluconeogenesis. Gluconeogenic enolase I shows substrate inhibition for 2-phosphoglycerate (glycolytic substrate) and glycolytic enolase II is substrate-inhibited by phosphoenolpyruvate (gluconeogenic substrate). The gluconeogenic reaction was inhibited up to 45% by physiological concentrations of fructose 1,6-bisphosphate. To test for cytological compartmentation, a method was developed for isolating microsomes. Effective enrichment of rough and smooth endoplasmic reticulum was demonstrated by electron microscopy. No evidence was obtained for any compartmentation of either enolases or other glycolytic enzymes.

Carbon↗
PubMed2006

Intracellular compartmentation of cardiac fibres from rainbow trout and Atlantic cod--a general design of heart cells.

In mammalian cardiomyocytes, mitochondria and adjacent ATPases with participation of creatine kinase (CK) constitute functional compartments with an exchange of ADP and ATP delimited from cytosolic bulk solution. The question arises if this extends to ectothermic vertebrates: their low body temperature and thinner cardiomyocytes with a lower density of membrane structures may reduce the need and structural basis for compartmentation. In saponin-skinned cardiac fibres from rainbow trout and Atlantic cod, we investigated mitochondrial respiration induced by endogenous ADP generated by ATPases and its competition for this ADP with pyruvate kinase (PK) in excess. At low Ca(2+) activity (pCa = 7.0), PK lowered ATP-induced respiration by 40% in trout and 26% in cod. At high Ca(2+) activity (pCa = 5.41), PK had no effect. Additionally, ADP release from the fibres was almost zero but increased drastically upon inhibition of respiration with 1 mM Na-azide. This suggests that fibres are compartmented. PK abolished creatine-stimulated respiration in trout suggesting a less tight coupling of CK to respiration than in mammals. In conclusion, intracellular compartmentation seems to be a general feature of vertebrate cardiomyocytes, whereas the role of CK is unclear, but it seems to be less important for energy transport in species with lower metabolism.

Adenosine Diphosphate↗