摘要:

Summry—This article is the fruit of reflections on the comparative study of centrosomal structures of various protists, and on recent data on the organization and composition of the centrosome of multicellular organisms. On the basis of a few significant situations encountered in protists, a model is proposed in which the metazoan centrosome represents a complex of three types of specialized microtubule‐organizing centers (MTOCs) of different origin and function, designated MTOC1, MTOC2, MTOC3. MTOCs1, presumably the most primitive, drive the mitosis. Associated with the chromosomes, they would be primitively included in the nuclear matrix acting as polar bodies in closed mitosis which characterizes many protists. MTOCs2 correspond to the centrioles, relics of basal bodies, whose primitive function was to engender a motor organelle. They differ from other cytoskeletal organizing centers only by their ubiquity and their 9+0 organization. MTOCs3, which may form stable structures of specific shape in some protists, control cellular morphology and intracellular traffic. The relationships between the various components and the nucleus are considered. Using a speculative scheme, we attempt to understand how this ensemble has diversified over the evolution of proti

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84770-8

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—TheCDC25gene product fromSaccharomyces cerevisiae, the prototype of the family of ras guanine nucleotide exchange factors, is expressed as a 180‐kDa polypeptide, tightly bound to a membrane fraction. The ability to complement acdc25defect is located in the 3′ part of the gene (codons 877–1589). Sequence analysis reveals only a short hydrophobic domain (residues 1459–1471) and no consensus sequence for post‐translational acylation. The SH3 domain present in the N‐terminal part of Cdc25p is not involved nor required for membrane localization, since the N‐terminal part of Cdc25p did not fractionate with a membrane pellet. In contrast, the C‐terminal part was attached to a 18000gpellet after subcellular fractionation and immunoblotting. This subcellular localization was conserved in aras1ras2double disruption mutant and in aira2disruption mutant. Immunofluorescence analysis showed a patchy staining, mainly at the periphery of the cells. These patches were quite distinct from actin patches by double immunolabeling. By analysing a set of truncated derivatives, the elements required for a particulate localization were restricted to r

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84771-X

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—The molecular mechanism whereby protein kinase C (PKC) molecules transduce signals into the cell nucleus is unknown. In this study, we provide evidence thatDictyostelium discoideumcontains PKCδ‐like protein that is localized in the nucleus. TheDictyosteliumPKCδ‐like protein has an apparent molecular mass of 76 kDa. This protein is already highly expressed in vegetativeDictyosteliumcells. The expression level remained constant up to 12 h of development, and sharply decreased after 16 h. The PKCδ‐like protein is phosphorylatedin vivoin response to cAMP and phorbol ester stimulation. Immunofluorescent studies, as well as subcellular fractionation experiments, have indicated thatDictyosteliumPKCδ‐like protein is permanently located in the nucleus. Our results may indicate that PKCδ‐like protein inDictyosteliumfunctions as a link between cAMP and the tumor‐promoting phorbol esters, and events that take pl

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84772-1

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—Extensive developmentally programmed DNA rearrangements, including thousands of internal deletions, occur in the differentiating somatic macronucleus inTetrahymena thermophila. Some deletion systems involve the use of multiple alternative deletion sites. We report here the cloning and the sequences of three new alternative deletion systems (RR, RP and B) obtained using genomic subtraction. The RP and RR deletion systems are 2 kb apart on chromosome IR, and both involve the removal of5 kb. All three deleted regions are very AT rich (∼ 80%) and do not appear to encode any protein. Sequences of the regions flanking the deletion junctions of all three systems revealed no sequence similarity among them nor with any previously reported deletion systems, suggesting that differentcis‐acting elements are involved for rearrangement. Unlike other deletion systems in ciliates, the B deletion system lacks short terminal direct repeats. Our results suggest an average of at least one alternative deletion system per 134 kb of micronuclear DNA and lead to an estimate that at least 25% of all deletion systems inTetrahymenautilize alternative ends. The genomic subtraction method employed in this study could prove useful for the isolation of alternatively deleted DNA in special‐purpose cases inTetrahymenaand other ciliates. The hybridization parameters for genomic subtraction worked out here for highly AT‐rich DNA may have wider u

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84773-3

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—The subcellular partitioning of the phosphoinositidase C (PIC) isoforms involved in signal transduction, with the selective localization of the PIC β1isoform in the nucleus, represents a crucial aspect of the complex mechanism of cell response to agonists. In order to further elucidate this phenomenon, we utilized human osteosarcoma Saos‐2 cells, transfected with the cDNA for rat PIC β1. In the cells overexpressing this isoform, immunocytochemical analyses at the electron microscope level reveal an increased synthesis at the cytoplasm and a significant accumulation within the nucleus of the protein. Interestingly, the sites of intranuclear localization are, as in wild type cells, the interchromatin domains. These results indicate that the transfected cells maintain the capability of accumulating the enzyme within the nucleus and can be considered a model for functional studies on the nuclear signal transduction also in response to specific ago

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84774-5

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—In mesangial cells (MC) isolated from streptozotocin (STZ)‐induced diabetic rat kidneys, sensitivity to bradykinin (BK) for the induction of cell division and collagen synthesis, was found to be lower than in normal MC. Nevertheless, decreased activities could be revertedin vitroby insulin, at non‐proliferative concentration (Girolamiet al(1995),Can J Physiol Pharmacol73, 848–853). The aim of the present study was to determine whether differences in the properties of diabetic MC could be ascribed to the diabetic stateper se, and/or to experimental conditions,ieculture replating. Through successive cell replating, normal and diabetic types of MC were compared in terms of proliferation, contraction, free calcium concentration in response to KCl depolarization, and in relation to the expression of two cytoskeleton proteins specific to muscle cells, myosin and dystrophin. Studies of proliferation, contraction and free calcium concentration consistently showed that passage 5 was a limit beyond which differences between the two MC types were very small and sometimes non‐significant. We found that the mean maximum contraction (MMC) and especially the proportion of contractile cells (PCC) among diabetic cells was lower than in normal MC. In addition, loss in proliferation activity and in [Ca2+]iconcentrations were also found to occur during these five early passages. Dystrophin, a new marker of contractile phenotype recently described in smooth muscle cell (Leiset al(1994)Cell Biol Toxicol10, 305), was first localized in MC and was compared with myosin also expressed in MC. However, during the course of cell replating and/or with the diabetic state, no visible quantitative changes were detected in the expression of the two contractile proteins. We conclude that cultured mesangial cells undergo phenotype modulations, as observed in other cells, in particular smooth muscle cells and consequently, comparative studies between normal and diabetic MC should not be carried out after the 5t

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84775-7

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—Plasma membrane fluidity of platelets (PLT) obtained from subjects with primary nocturnal enuresis (PNE) and healthy controls was investigated before and after addition of desmopressin (DDAVP). Membrane fluidity was studied by measuring steadystate fluorescence anisotropy of 1‐(4‐trimethylammoniumphenyl)‐6‐phenyl‐1, 3, 5‐hexatriene incorporated into PLT plasma membrane. Our results show an increase in membrane fluidity at the surface level of PLT from subjects with PNE. Moreover, the addition of DDAVP induces a stable and significant decrease of membrane fluidity in both groups. These results suggest alterations of the lipid order in the exterior part of the PLT plasma membrane from pati

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84776-9

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—Immunofluorescence microscopic observations indicated that a monoclonal antibody, Vmp 18, raised against the peptide 199–208 of murine interleukin 1α, cross‐reacted with an antigenic determinant ofDrosophilathorax muscles. Immunoelectron microscopic analysis showed that the gold particles were mainly localized in the Z‐line which is the attachment site of thin filaments from adjacent sarcomeres. On the contrary, the antibody failed to mark the Z‐line in vertebrate skeletal muscle. A Western blot of total protein extract fromDrosophilathorax muscles bound a protein of 43 kDa. Our observations suggest that the Vmp 18 antibody could contribute to clarify the composition of the Z‐line in insect's fl

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84777-0

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—In the present study we describe the induction of changes in intracellular fluorescein fluorescence polarization (IFFP) in lymphocytes undergoing activation with a variety of stimulants. These stimulants included the lectins phytohaemagglutinin (PHA), concanavalin (ConA), pokeweed mitogen (PWM) and anti‐CD3 antibody. Changes in IFFP were detected in individual cells using the Cellscan apparatus. Our results show that by employing mitogenic concentrations of PHA, as revealed in a [3H]‐thymidine incorporation assay, a decrease in the IFFP in human peripheral blood lymphocytes (PBL) occurred within 40 min. ConA and anti‐CD3 affected similarly IFFP, whereas PWM, a B lymphocyte lectin, had no effect on IFFP at the concentrations employed. Kinetic analysis revealed that changes in IFFP occurred within 20–40 min after exposure to the stimulants and lasted for 24 h. Our results show that stimulants which activate CD3+lymphocytes caused immediate changes in IFFP, in an enriched population of human PBL. The possible mechanisms involved in IFFP modulation following exposure to selected stimulants are

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84778-2

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—The influence of metal contamination on the marine algaTetraselmis suecicawas investigated at physiological and ultrastructural levels. For this analysis, the growth response of this microalga was studied after the addition of various concentrations of heavy metals (Cd, Cu). The concentration corresponding to 50% growth inhibition (IC50) and the number of days per cell cycle (Td) studied, revealed that the toxic effects of copper are heavier than those of cadmium. In the case of copper contamination, the Td grows with increasing metal concentration in the culture medium, while it remains unchanged during the cadmium contamination. The toxicity of cadmium, only observed in the latency phase of growth, suggests an adaptation phenomenon ofT suecicato this metal. Ultrastructural changes in response to pollutants were investigated; copper induced cytoplasmic vacuolisation, organelle changes, appearance of cells with multilayered cell walls and excretion of organic matter. In the case of cadmium contamination, ultrastructural changes mainly affected the osmiophilic vesicles, of which both number and volume increased with increasing metal concentration in the culture medium. The results of X‐ray microanalysis revealed that Cd and Cu were strongly present in excreted organic matter and osmiophilic vesicles. The latter can be excreted during cell division, thus participating in detoxification processes. Intracellular cadmium incorporation proved that some toxic effects of this metal are a result of interaction with endogenous cellular constituents. In the case of copper contamination, the presence of copper in walls of a multilayered cell suggests that these structures constitute an additionnal adsorbing area for this element, reducing metal free concentration in the medium. Mechanisms of metal detoxification ofTetraselmis suecicaare discus

ISSN:0248-4900    

DOI:10.1016/0248-4900(96)84779-4

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY