摘要:

Summary—The review focuses on calcium accumulation by secretory organelles. The observation that secretory granules contain variable and often important quantities of calcium (1–200 mM of total calcium) can be interpreted as a maturation index. A progressive loading with calcium would be permitted by a Ca2+‐transport mechanism on the granular membrane and calcium‐binding molecules in the granular core. The saturation of this store by the stimulus‐induced calcium transient would permit in mature (calciumloaded) granules the ionic crisis leading to exocytosis. The inside of secretory organelles being acidic, calcium influx into the granule can be driven by calcium‐proton exchange. The calcium‐proton exchanger could be

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90128-N

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—By light and electron microscope cytochemistry we characterized the interphase nucleus ofLacandonia schismatica, the only known species of the new plant family Lacandoniaceae, whose most peculiar feature is the inverted position of the sexual organs, an aspect never found before among flowering plants. Furthermore, we compare it toTriuris alata, a related species, toVoyria aphylla(a dicotyledon), toGymnosiphon divaricatus(a monocotyledon) and also to saprophytes. The reticulated chromatin ofL schismaticaandT alatais similar to that of other monocotyledons. In addition, we describe a unique type of RNP granules in the interchromatin space which are about 32 ± 3 nm SD in diameter and occur as huge clusters. They are intermediate in size and spatial distribution between inter‐ and peri‐chromatin granules. We term them ‘Lacandoniagranules’. The granules were also found inT alata. They are 31 ± 2 nm in diameter. No significant differences in size were observed between them (P>0.05). Synaptonemallike complexes and ring‐shaped structures were seen in interphase nuclei of somatic cells of these species. Coiled and nucleolus‐associated bodies, as well as centromeres were also found in these two organisms. On the contrary,VaphyllaandG divaricatusdisplay a chromocentric nuclear organization. The nuclear similarities betweenL schismaticaandT alatasuggest extremely close phylogenetic relationshi

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90129-O

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The mode of association of microtubules (MTs) with the plasmalemma in epidermal tendon cells of the river crab,Potamon dehaaniwas studied by thin‐section electron microscopy. In the leg muscle, the tendon cells connect striated muscle cells with the cuticle, forming specialized junctions at both ends. At the muscle‐tendon cell junction, the apposed plasmalemmas are interdigitated in a zig‐zag pattern separated by a uniform space of about 50 nm, where the basal lamina is shared by two cells. At the tendon cell‐cuticle junction, the plasmalemma of the tendon cell forms many conical invaginations, into which dense fibrous material extends from the cuticle. Inside the tendon cell, numerous microtubules run parallel to the direction of tension transmission and are arranged into parallel bundles of various sizes. Within such bundles, fine filamentous structures cross‐link adjacent MTs. MTs span the entire length of the cell and attach at their both ends to the junctional domains of the plasmalemma. The junctional plasmalemma is characterized by formation of an electron‐dense undercoat, through which MTs are connected with the plasmalemma proper. The ultrastructural features of MT association with the plasmalemma are basically the same at both junctions. At the junctions, MTs usually terminate with free ends and are linked laterally to the plasmalemmal undercoat with fine filamentous structures. These observations emphasize the role of the plasmalemmal undercoat as a device of the attachment of MTs to th

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90130-S

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—We have studied by way of confocal laser scanning microscopy the subcellular localization of cyclin B inDrosophila‐cultured cells and report here evidence that a part of the cyclin B cell pool is closely associated with the centrosome. This cyclin B centrosomal signal is strong in prophase and metaphase but disappears during anaphase. Moreover, the signal is absent in the acentriolarDrosophilacell line 1182‐4. These results put forward additional arguments suggesting that the centrosome plays an important role in the control of the cell

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90131-J

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—We have developed a reconstituted model system to study the interaction of the Golgi membranes isolated from rabbit liver with taxol‐stabilized bovine‐brain microtubules without microtubule‐associated proteins (MAPs). The Golgi membranes are associated with microtubules. The sheets of vesicles and the membranous tubules are observed along microtubules by direct visualization using differential‐interference‐contrast, dark field, or fluorescence microscopy. The monoclonal antibody against Golgi membranes suggests that the Golgi membranes, but not the contaminating vesicles, are interacting with microtubules. The degree of association is assayed quantitatively using rhodamine‐labeled microtubules after separation of the complex from unbound microtubules by centrifugation upon sucrose gradient. The association is inhibited by crude MAPs, purified MAP2, or 1.0 mM ATP. However, the association neither requires the cytosol from rat liver or bovine brain norN‐ethylmaleimide, brefeldin A, or GTP‐γ‐S. The association is mediated by trypsin‐sensitive peripheral protein(s)

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90132-K

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—Membrane fluidity of erythrocytes obtained from 15 children with trisomy 21 and 20 healthy controls were studied by measuring steady‐state fluorescence anisotropy and fluorescence lifetime of 1,6‐diphenyl‐1,3,5‐hexatriene (DPH) and 1‐(4‐trimethylammoniumphenyl)‐6‐phenyl‐1,3,5‐hexatriene (TMA‐DPH) incorporated in hemoglobin‐free erythrocyte membranes. Our results demonstrate a significant decrease in DPH fluorescence anisotropy and a significant increase in TMA‐DPH fluorescence anistropy in erythrocytes from subjects with trisomy 21. No significant differences between the two groups were observed in the fluorescence lifetime of DPH and TMA‐DPH. These data suggest an increase in membrane fluidity in the interior part of the membrane and a decrease in fluidity at the lipid‐water interface region. This could be in part attributed to an increased

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90133-L

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—cdc25 proteins are universally involved in the control of cell division. Using an original method of sequence analysis, cdc25 proteins from different sources were compared to protein phosphatases. Protein phosphatases could clearly be characterized as two distinct protein families, the phospho‐seryl/threonyl phosphatases, and the phospho‐tyrosyl phosphatases. None of the cdc25 proteins analyzed fitted with the phospho‐tyrosyl phosphatases, indicating that if they indeed possess this biochemical activity, they form a distinct phosphatase protein group. Unexpectedly, higher eucaryotic cdc25 proteins (from human and fly) were found to be structurally related to phospho‐seryl/threonyl phosphatases. These results fit well with the expected function of the proteins, associated solely in higher eucaryotes, to dephosphorylation of threonine in the cell cycle control pro

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90134-M

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The enzyme geranylgeranylpyrophosphate synthase (GGPPS), which plays a key role in the synthesis of diterpene compounds, carotenoids and higher terpenoids, has been localized inCapsicumfruit cells by ultrastructural immunogold cytochemistry, after conventional chemical fixation of tissues and quick‐freezing followed by freeze‐substitution of isolated chloroplasts and chromoplasts. In agreement with previous biochemical studies on cell fractions, the enzyme seems restricted to the plastid compartment. Together with the phenotypic changes of the fruit and the ultrastructural modifications of the plastids during the transition of chloroplasts to chromoplasts, the amount of immunolabelling over plastid sections increases more than a ten‐fold factor in the course of fruit ripening. In chemically fixed tissues, the gold labelling of chloroplasts is very faint and erratically localized whereas in further transition stages, and in chromoplasts, most of the gold particles surround the developing plastoglobuli, which are the characteristic carotenoid‐bearing structures. Because of the very low and inconstant labelling of chloroplasts in green fruits after chemical fixation, cryofixed and acetone freeze‐substituted purified plastids were used as a model system for an accurate localization of the enzyme in these organelles. Quick‐freezing in buffered sucrose by slam‐freezing on a cold copper block results in optimal preservation of the plastids and improved labelling of GGPPS. The enzyme is not scattered at random throughout the stroma. Gold particles are concentrated in distinct stroma regions, and especially at the sites of initiation of stroma globuli which are the early structural event of carotenoid accumulation. A few gold particles are also present on the margins of thylakoids and, presumably, on the plastid envelope. This paper reports further evidence of the central role of the plastid compartment in the production of C20 isoprenoid intermediates in the plant cell, shows the spatial relationship of the enzyme geranylgeranylpyrophosphate synthase with the plastid substructures and the existence of several GGPPS pools within the plastids. It demonstrates the interest of cryo‐methods for an accurate localization of various enzym

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90135-N

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The effects on vascular wound repairin vitroof aFGF and TGF‐β, growth factors having opposite influences on endothelial cell growth and angiogenesis, were studied using as a model a mechanical lesion of confluent endothelium. Modulation by heparin of the activities of these growth factors during the repair process was also examined. Whereas heparin alone inhibited repair by lowering both cell proliferation and cell migration, TGF‐β alone mainly inhibited cell proliferation. When added together, TGF‐β and heparin exerted a combined inhibitory effect resulting in a residual lesion 50% larger than in controls. aFGF alone accelerated lesion coverage and this effect was enhanced by 40% over control values when heparin was added with aFGF. This acceleration was slightly (less than 10%) but consistently diminished by TGF‐β. Cell density in confluent unwounded areas was increased by 40% in the presence of aFGF, but TGF‐β diminished cell density by 20%. A small (30%) increase in intracellular cAMP was measured whenever aFGF was present during the repair process. In comparison, intracellular cAMP inducing agents (forskolin, dbcAMP) accelerated cell migration by 20% during lesion recovery without affecting cell proliferation or density. The present results show that the inhibitory effects of TGF‐β during vascular wound repair are opposed by aFGF. Furthermore, heparin (or heparan sulfatesin vivo) modulates growth factors having activating or inhibiting functions and thus plays a regulatory role during the repair process. cAMP‐inducing substances other than growth factors are able to acce

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90136-O

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY