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1.
Cell differentiation involves the development of a new cytoplasm containing a set of specialized organelles such as cilia and flagella which are placed in the cell with a predetermined orientation. Arguments are put forward to show that the orientation of the flagellar apparatus could be brought about by a macromolecular structural bridge between the nucleoid and the assembling flagellar apparatus, the orientation being determined by the spatial geometry inherent in the folding of the DNA. An analysis of differentiation in unicelled eukaryotes suggests that the same basic mechanism of a structural bridge could also apply to the orientation of their cilia and flagella and perhaps may have a more general application in the positioning of cytoplasmic organelles.  相似文献   

2.
Cells contain numerous, molecularly distinct cellular compartments that are not enclosed by lipid bilayers. These compartments are implicated in a wide range of cellular activities, and they have been variously described as bodies, granules, or organelles. Recent evidence suggests that a liquid–liquid phase separation (LLPS) process may drive their formation, possibly justifying the unifying term “droplet organelle”. A veritable deluge of recent publications points to the importance of low‐complexity proteins and RNA in determining the physical properties of phase‐separated structures. Many of the proteins linked to such structures are implicated in human diseases, such as amyotrophic lateral sclerosis (ALS). We provide an overview of the organizational principles that characterize putative “droplet organelles” in healthy and diseased cells, connecting protein biochemistry with cell physiology.  相似文献   

3.
K. A. Mikrjukov 《Protoplasma》1995,188(3-4):186-191
Summary A study of the structure, function, and development of extrusive organelles (microtoxicysts) in the unusual bacteriovorous rhizopodPenardia cometa is performed. Microtoxicysts are located in the cortical cytoplasm of the cell body and in special thickenings on reticulopodia. Similar types of extrusomes have been observed in some cercomonads. The microtoxicysts are organized as membrane-bound vesicles of a complex form. An oviform-conical axial element lies inside each vesicle and is directed with its narrower end towards the plasma membrane. An internal cylindrical tube occupies the central part of the axial element; it is turned out as the organelle is shot out. The extrusomes ofP. cometa originate from and develop in derivates of the endoplasmic reticulum, the initial diameter of proextrusome vesicles is twice the diameter of the mature organelles. At late stages of maturation the microtoxicysts adopt their characteristic form and orientation. The mode of construction, ejection and development is compared with that in some other carnivorous and bacterivorous protists.  相似文献   

4.
Microtubule cytoskeleton is a dynamic structure involved in the maintenance of eukaryote cell shape, motion of cilia and flagellum, and intracellular movement of vesicles and organelles. Many antibodies against tubulins have been described, most of them against the C-terminal portion, which is exposed at the outside of the microtubules. By generating a novel set of monoclonal antibodies against the cytoskeleton of Trypanosoma cruzi, a flagellate protozoan that causes Chagas' disease, we selected a clone (mAb 3G4) that recognizes β-tubulin. The epitope for mAb 3G4 was mapped by pepscan to a highly conserved sequence motif found between α-helices 11 and 12 of the C-terminus of β-tubulin in eukaryotes. It labels vesicular structures in both T. cruzi and mammalian cells, colocalizing respectively with a major cysteine protease (Cruzipain) and lysosome associated protein (LAMP2) respectively, but it does not label regular microtubules on these cellular models. We propose that the epitope recognized by mAb 3G4 is exposed only in a form of tubulin associated with endosomes.  相似文献   

5.
Endosymbiotic relationships are common across the tree of life and have had profound impacts on cellular evolution and diversity. Recent molecular investigations of the amoeba Paulinella chromatophora have raised a timely and important question: should obligatory intracellular cyanobacteria in Paulinella be considered new organelles, or do plastids and mitochondria hold a unique stature in the history of endosymbiotic events? We argue that drawing a sharp distinction between these two organelles and all other endosymbionts is not supported by accumulating data, neither is it a productive framework for investigating organelle evolution.  相似文献   

6.
The pollen grain maturation in Magnolia × soulangeana was studied ultrastructurally and cytochemically using both the light and transmission electron microscope. Emphasis was given on the storage lipid bodies of the vegetative cell (VC) and their interaction with other cell organelles. Stereological analysis of electron micrographs was performed to evaluate the variation in volume density (VV), surface density, and surface-to-volume ratio (S/V) of various cell organelles during pollen maturation. The size and numerical density of the lipid bodies, and their frequency of association with other cell organelles, were also determined. It was noted that during pollen ontogeny and maturation, the lipid bodies changed their pattern of distribution in the VC cytoplasm, which may be a good marker for the succeeding stages of pollen development. Also, the size, osmiophily, and VV of the lipid bodies were progressively reduced during pollen maturation whereas the S/V was significantly increased. This seems to indicate that the lipid bodies are mobilized in part during this period of pollen maturation. In particular, the intermediate and mature pollen showed a high percentage of lipid bodies establishing a physical contact with either glyoxysomes, either protein storage vacuoles, or small vesicles presumably originated from dictyosomes. This physical contact was found in both the chemically fixed and rapid freeze-fixed pollen indicating that it is neither artifactual nor casual. On the basis of this intimate association with other cell organelles and the morphometric analysis performed, we suggest that the mobilization of lipid bodies is likely mediated not only by glyoxysomes but also by other catabolic pathways involving the interaction of lipid bodies with either protein storage vacuoles or small Golgi vesicles.  相似文献   

7.
Together with micronemes and rhoptries, dense granules are specialised secretory organelles of Apicomplexa parasites. Among Apicomplexa, Plasmodium represents a model of parasites propagated by way of an insect vector, whereas Toxoplasma is a model of food borne protozoa forming cysts. Through comparison of both models, this review summarises data accumulated over recent years on alternative strategies chosen by these parasites to develop within a parasitophorous vacuole and explores the role of dense granules in this process. One of the characteristics of the Plasmodium erythrocyte stages is to export numerous parasite proteins into both the host cell cytoplasm and/or plasma membrane via the vacuole used as a step trafficking compartment. Whether this feature can be correlated to few storage granules and a restricted number of dense granule proteins, is not yet clear. By contrast, the Toxoplasma developing vacuole is decorated by abundantly expressed dense granule proteins and is characterised by a network of membranous nanotubes. Although the exact function of most of these proteins remains currently unknown, recent data suggest that some of these dense granule proteins could be involved in building the intravacuolar membranous network. Conserved expression of the Toxoplasma dense granule proteins throughout most of the parasite stages suggests that they could also be key elements of the cyst formation.  相似文献   

8.
The light-gradient photovoltage from photosynthetic organisms and organelles is thought to arise from the primary charge separation in the reaction centers. The current explanation of the effect is the stronger excitation of the membrane side of a vesicle facing the light source than the one on the opposite side. Together with the known orientation of reaction centers, this explanation predicts unequivocally the polarity of the photovoltage. However, a polarity opposite to the one expected has often been reported. A dependence of the polarity on the wavelength has been published but no explanation was given (Gräber, P., and H.-W. Trissl. 1981. FEBS Lett. 123:95-99). Here we report on a theoretical treatment of light propagation and interference in pigmented and nonpigmented multilayers. A model calculation is carried out for a pair of membranes, demonstrating the wavelength-dependent light distribution as well as the relative photovoltage and its polarity. When the membranes contain no chromophores or when the absorption coefficient is low, the predicted polarity to that expected from a simple macroscopic absorption behavior. The model is tested by comparing new photovoltage data obtained at 532 nm as well as in the blue and red absorption bands of chlorophyll in chloroplasts. It is concluded that outside the main absorption bands the amplitude and polarity of the photovoltage is determined by the ratio of the refractive indices of the membrane and the medium.  相似文献   

9.
Why have organelles retained genomes?   总被引:14,自引:0,他引:14  
The observation that chloroplasts and mitochondria have retained relics of eubacterial genomes and a protein-synthesizing machinery has long puzzled biologists. If most genes have been transferred from organelles to the nucleus during evolution, why not all? What selective pressure maintains genomes in organelles? Electron transport through the photosynthetic and respiratory membranes is a powerful - but dangerous - source of energy. Recent evidence suggests that organelle genomes have persisted because structural proteins that maintain redox balance within bioenergetic membranes must be synthesized when and where they are needed, to counteract the potentially deadly side effects of ATP-generating electron transport.  相似文献   

10.
The sphere organelles (spheres) ofXenopus and other amphibian oocytes are known to contain small nuclear ribonucleoprotein particles (snRNPs) and have been suggested to play a role in snRNP complex assembly. Coupled with the similarities that exist between spheres and nucleoli and the quantitative and kinetic aspects of snRNA synthesis in theXenopus oocyte, we have investigated whether or not the U snRNA encoding genes are amplified inXenopus oogenesis, the spheres being possible sites for the location of such extrachromosomal gene copies. By applying a number of quantitative nucleic acid hybridization procedures to both total and fractionated oocyte and somatic DNA, employing both homologous and heterologous U snRNA gene probes and suitable amplification and non-amplification control probes, we show that the U snRNA genes do not undergo any major amplification inXenopus oogenesis. Therefore, the analogy between the sphere organelles and nucleoli appears to be limited. The role of the spheres and their relationship to other snRNP containing structures, specifically B snurposomes, and the sphere organizer loci remains obscure.by A. Spradling  相似文献   

11.
Plant organelles are highly motile, with speed values of 3–7 m m/s in cells of land plants and about20–60 m m/s in characean algal cells. This movement is believed to be important for rapid distribution of materials around the cell, for the plant's ability to respond to environmental biotic and abiotic signals and for proper growth. The main machinery that propels motility of organelles within plant cells is based on the actin cytoskeleton and its motor proteins the myosins.Most plants express multiple members of two main classes:myosin VIII and myosin XI. While myosin VIII has been characterized as a slow motor protein, myosins from class XI were found to be the fastest motor proteins known in al kingdoms. Paradoxically, while it was found that myosins from class XI regulate most organelle movement, it is not quite clear how or even if these motor proteins attach to the organelles whose movement they regulate.  相似文献   

12.
Mammalian lipid droplets (LDs), first described as early as the 1880s, were virtually ignored for more than 100 years. Between 1991 and the early 2000s, however, a series of discoveries and conceptual breakthroughs led to a resurgent interest in obesity as a disease, in the metabolism of intracellular triacylglycerol (TAG), and in the physical locations of LDs as cellular structures with their associated proteins. Insights included the recognition that obesity underlies major chronic diseases, that appetite is hormonally controlled, that hepatic steatosis is not a benign finding, and that diabetes might fundamentally be a disorder of lipid metabolism. In this brief review, I describe the metamorphosis of LDs from overlooked globs of stored fat to dynamic organelles that control insulin resistance, mitochondrial oxidation, and viral replication.  相似文献   

13.
At the core of regenerative medicine lies the expectation of repair or replacement of damaged tissues or whole organs. Donor scarcity and transplant rejection are major obstacles, and exactly the obstacles that stem cell based therapy promises to overcome. These therapies demand a comprehensive understanding of the asymmetric division of stem cells, i.e. their ability to produce cells with identical potency or differentiated cells. It is believed that with better understanding, researchers will be able to direct stem cell differentiation. Here, we describe extraordinary advances in manipulating stem cell fate that show that we need to focus on the centrosome and the centrosome-derived primary cilium. This belief comes from the fact that this organelle is the vehicle that coordinates the asymmetric division of stem cells. This is supported by studies that report the significant role of the centrosome/cilium in orchestrating signaling pathways that dictate stem cell fate. We anticipate that there is sufficient evidence to place this organelle at the center of efforts that will shape the future of regenerative medicine.  相似文献   

14.
In vivo’ microspectroscopy represents an effective and reliable technique to study pigment distribution and even composition. Contrary to traditional extractive techniques, it preserves the integrity of biological structures, without modifying the nature of the pigments. The spectroscopic apparatus described here is very simple and consists of a standard microscope equipped with an interference filter monochromator, a photomultiplier, and two combined pinhole diaphragms. As examples, absorption spectra of an eyespot and a chloroplast of Euglena gracilis are presented.  相似文献   

15.
16.
It has been shown that myosin molecules attached to Covaspheres can "walk along" polar actin filament in vitro. The driving force for this movement seems to explain only about 1% of the isometric tension developed by a muscle fibre. Therefore, the driving force for the bead movement seems to be incompatible with that found in muscle, and the bead movement cannot be considered as a model for muscle contraction. The origin of the bead movement may be related to a "molecular jet" process, resulting from the rapid ejection of the MgATP splitting products. This "molecular jet" might also explain the movements of many cellular organelles.  相似文献   

17.
Isolates of aflatoxin-producing strains of Aspergillus grow on autoclaved and field-grown (lesser extent) Glycine max beans. Both mixed and aflatoxin B1 inhibit G. max, cv. Essex bean germination and elongation of either attached or excised cultured roots. Because B1 impairs the latter roots' ability to intracellularize [14C]-leucine, it may alter plasmalemma structure and/or function. To determine whether incubation of excised roots for 18 hours in toxin-containing medium could affect cellular membrane chemical content, organelles were isolated by differential centrifugation (1 000, 40 000, and 80 000 xg) of homogenates and characterized chemically. Statistically significant differences between treated and untreated roots in acid insoluble protein but not either sterol or lipid phosphorus levels were observed for both 40,000 and 80,000 xg pellets. Protein and sterol recoveries were 81 (treated) and 84 (untreated) % for the former and 77 (treated) and 79 (untreated) % for the latter. Lipid phosphorus recoveries were 87.3 (treated) and 136 (untreated) % with and 96 (treated) and 83 (untreated) without membrane stabilization. Protein:sterol:lipid phosphorus were 35.74.51 (1 000 xg), 18.93.61 (40000 xg), 26.34.61 (80 000 xg) and 1,010291 (80 000 xg supernatant) for untreated and 36.93.31 (1,000 xg), 23.13.81 (40 000 xg), 36.24.81 (80 000 xg) and 1,05321.71 (80 000 xg supernatant) for treated roots. Significant differences in RNA content between treated and untreated roots were found for both 1 000 and 40 000 xg pellets but not for the 80 000 xg pellet and its supernatant. Whereas a significant increase in the 1 000 xg pellet occurred upon treatment, a decrease was noted for the 40 000 xg pellet but not for the 80 000 xg pellet and its supernatant. Similar pH 6 (plasmalemma marker enzyme) and 9 (mitochondrial marker enzyme) K+-stimulated ATPase activities were demonstrated for 40 000 and 80 000 xg pellets. The 1 000 xg pellet contained greater than 50% of the NADH-cytochrome c-reductase activity (endoplasmic reticulum marker enzyme) recovered from fractions examined for this activity which was absent from the 40 000 xg pellet. Both the 80 000 xg pellet and its supernatant possessed equivalent reductase activities. Inosine diphosphatase activity (dictyosome marker enzyme) was not present in 1 000 xg pellets obtained from either treated or untreated roots but was in both 40 000 and 80 000 xg pellets. Based on these results, a tentative assignment of organelles to each fraction (xg force) is reported.Abbreviations used AFB1 aflatoxin B1 - AFB2 aflatoxin, B2 - AFG1 aflatoxin G1 - AFG2 aflatoxin G2 - ATPase adenosine triphosphatase - IDPase inosine diphosphatase - NADH reduced nicotinamide-adenine dinucleotide - PCA perchloric acid - TCA trichloroacetic acid - 2, 4-D 2,4-dichlorophenoxyacetic acid Aided by grant IN-127 from the American Cancer Society to WVD and funds from the Departments of Biology, West Virginia University and Virginia Commonwealth University as well as a Sigma Xi award to JMD.  相似文献   

18.
1. The developmental pattern and effect of cortisone on acid beta-galactosidase and neutral beta-galactosidase were studied in postnatal rats by a recently proposed method for their independent determination. 2. After birth the acid beta-galactosidase activity increases in the ileum, whereas it decreases slightly in the jejunum. On day 16 after birth the activity in the ileum decreases and in 20-day-old rats activity in both parts of the intestine decreases to adult values. In suckling animals the activity in the ileum exceeds the jejunal activity severalfold and in adult animals the activity in the jejunum is slightly higher than that in the ileum. 3. Neutral beta-galactosidase activity is high after birth and decreases in both jejunum and ileum after day 20 after birth. In 12-20-day-old rats activity in both parts is essentially the same, but in adult animals jejunal activity exceeds ileal activity four-to five-fold. 4. Cortisone (0.5, 2.0 or 5.0mg/100g body wt. daily for 4 days) does not influence the activity of either enzyme in 60-day-old rats. Acid beta-galactosidase activity is decreased after cortisone treatment in 8-, 12-, 16-and 18-day-old rats, with sensitivity to cortisone increasing with the approach of weaning. No effect of cortisone on acid beta-galactosidase is seen in 8-day-old rats. Neutral beta-galactosidase activity is increased in the ileum of 8-, 12-, 16- and 18-day old rats, but only in the jejunum of 8-and 12-day-old rats.  相似文献   

19.
20.
CIRL-1 also called latrophilin 1 or CL belongs to the family of adhesion G protein-coupled receptors (GPCRs). As all members of adhesion GPSR family CIRL-1 consists of two heterologous subunits, extracellular hydrophilic p120 and heptahelical membrane protein p85. Both CIRL-1 subunits are encoded by one gene but as a result of intracellular proteolysis of precursor, mature receptor has two-subunit structure. It was also shown that a minor portion of the CIRL-1 receptor complexes dissociates, producing the soluble receptor ectodomain, and this dissociation is due to the second cleavage at the site between the site of primary proteolysis and the first transmembrane domain. Recently model of independent localization p120 and p85 on the cell surface was proposed. In this article we evaluated the amount of p120-p85 complex still presented on the cellular membrane and confirmed that on cell surface major amount of mature CIRL-1 presented as a p120-p85 subunit complex.  相似文献   

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