摘要:

Summary—A cytological analysis was performed in order to determine how the formation of the metaphase I‐ and metaphase II‐spindles is dependent upon p34cdc2kinase activity and protein synthesis during the meiotic maturation ofXenopusoocytes. The p34cdc2kinase activity increases abruptly during the prophase‐prometaphase I transition, then drops to a minimum level at the metaphase I/anaphase I transition and further increases again until reaching a maximum stable level at metaphase II. The injection of an indestructible cyclin B into oocytes arrests the maturation process at the onset of anaphase I and prevents the re‐increase of p34cdc2activity which accompanies normal entry into metaphase II. Inhibition of protein synthesis between the germinal vesicle breakdown and the onset of metaphase I spindle induces exit from M‐phase and leads to an ‘interphase‐like’ state characterized by the organization of nuclear‐like structures. In contrast, inhibition of protein synthesis at metaphase II stage does not affect the metaphase II spindle nor p34cdc2activity, indicating that metaphase I‐ and metaphase II‐spindles are not regulated by the same effectors. When protein synthesis is inhibited before induction of M‐phase by MPF transfer, it prevents the formation of the metaphase I spindle, despite a transient elevated level of p34cdc2activity. To dissociate the role of protein synthesis and of p34cdc2kinase activity, the indestructible cyclin B was microinjected in the absence of protein synthesis. This allows thein vivomaintenance of a stable p34cdc2activity. Under these conditions, microtubules do not polymerize and no metaphase I spindle is formed, demonstrating that the synthesis of proteins, different from cyclin B, is required for the organization of the metaphase I spindle in addition to the pr

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80181-9

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summary—Transcription of cell‐specific vasopressin and oxytocin genes as well as transcription of those housekeeping genes responsible for general metabolic activation and cellular hypertrophy is induced in supraoptic hypothalamic neurons by rises in plasma osmolarity. In this study, the nuclear volume, the ultrastructure of chromatin and the number and distribution of nuclear particles in the cell nuclei of supraoptic neurons of 3‐month‐old male Sprague‐Dawley rats were analyzed after osmotically induced activation of transcription by periods of acute (1 day) and chronic (6 days) dehydration, and after halting the stimulation by rehydration of animals. The nuclear volume and the ultrastructure of chromatin were assessed on ultrathin sections. The number and distribution of nuclear particles were assessed on freeze‐fracture replicas. The initial phase of osmotically induced enhancement of transcription was accompanied by an increase in nuclear volume and by a partial replacement of nuclear particles of large diameter (>11 nm) by smaller nuclear particles. This latter change affected predominantly the nuclear periphery (0–1000 nm from the nuclear membrane) and occurred simultaneously with a partial decondensation of chromatin clusters that may be related to chromatin unfolding. In chronically stimulated animals, the decondensation of chromatin and the replacement of large nuclear particles by smaller ones was enhanced in the nuclear periphery and was partially propagated to the interior of the nucleus. After suppression of cellular activation by rehydration of animals, the number of nuclear particles returned to control levels in the nuclear periphery while in the center of the nucleus the number of small particles decreased and the number of large particles increased as compared to control values. These results, together with the observation that in unstimulated cells the nuclear periphery and the nuclear interior differ in their composition of nuclear particles, evidence a structural and functional compartmentalization in the cell nucleus of supra

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80182-0

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summary—We have previously shown the presence, in the amplified DNA of aDrosophilacell line resistant to N‐phosphonacetyl‐L‐aspartate (PALA), of two units of 150 kb and 120 kb respectively duplicated and amplified. The two joints (J1 and J2) linking these units as well as their respective wild‐type counterparts have been sequenced. Sequence analysis indicates that a region of theDrosophilagenome which corresponds to the proximal boundary of the 150 kb unit is common to both joints. In addition to this common region, the J1 junction possesses a 26‐nucleotide sequence belonging to the J2 junction. This indicates that the J2 junction was the first formed, and that J1, therefore, results from recombination between J2 and a region of the wild‐type genome 120 kb distal to J2. Sequence analysis also reveals that the joints result from illegitimate recombination between unrelated regions. AT‐rich sequences, strand bias composition and putative topoisomerase I and II sites were found in at least one of the two parental sequences involved in the formation of the joints. On the basis of these results we can hypothesize that after two illegitimate recombinations between sister chromatids, leading first to J2 and then to J1, the amplification may have arisen by a series of homologous (unequal crossing‐over) or illegitimate recombinations, or by an intrachromosom

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80183-2

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summary—Balbiani ring premessenger ribonucleoprotein (RNP) particles are built from a 7‐nm RNP fiber which is tightly folded into a ring‐shaped RNP ribbon. Isolated particles are known to disintegrate in an all‐or‐none fashion upon RNase A treatment. In the present study we investigated whether this mode of disintegration is dependent on an intact particle structure or is inherent in the 7‐nm fiber. When treated at low ionic strength, the Balbiani ring (BR) particles lost their higher order structure and the 7‐nm fiber was unpacked, as evidenced by sucrose gradient sedimentation and electron microscopy. When treated with RNase A, unfolded as well as intact particles disintegrated in the all‐or‐none fashion, with similar kinetics and without apparent intermediates. Proteinase K treatment, however, obliterated this pattern: the protein‐free particle RNA degraded progressively. As the typical disintegration pattern of the particles was not altered by unfolding, but was lost by deproteinization, the all‐or‐none mode of disintegration is likely to be a propert

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80184-4

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summary—Ultrastructural changes of the germinal vesicle during the growth of rabbit oocytes were studied by means of light and electron microscopy,3H‐uridine autoradiography, Ag‐NOR staining and E‐PTA staining. Particular interest was paid to the nucleologenesis and condensation of chromatin. In contrast to other mammalian species, chromosome condensation in rabbit oocytes occurred concomitantly with rRNA synthesis‐dependent nucleolar compaction and preceded nuclear envelope breakdown and resumption o

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80185-6

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summary—Human luteal granulosa cells, harvested from preovulatory follicles duringin vitrofertilization attempts, were cultured in a serum‐precoated substratum (‘serum cells’) or on a collagen matrix (‘collagen cells’). Concerning the ‘serum cell’ model, E2 secretion was very low in the absence of androgen; when androstenedione was added to the culture medium, cells secreted 180 ± 52 pmol/ml/24 h of estradiol, 440 ± 78 pmol/ml/24 h of testosterone and lower quantities of estrone and estriol. Follicle stimulating hormone induced a significant increase in estradiol and estriol, while the secretion of the other steroids was not altered. The secretion of progesterone was 3.15 ± 1 nmol/ml/24 h and significantly enhanced by luteinizing hormone (+ 95%;P<0.01). The secretions of 17α‐hydroxyprogesterone and 20α‐dihydroprogesterone were low and not modified by luteinizing hormone. ‘Collagen cells’, in basal conditions, showed an increased secretion of estradiol (+ 50%,P<0.05), became rounded and were less responsive to gonadotropins when compared with ‘serum cells’. Thus, the use of a collagen matrix, similarly to gonadotropins, stimulated granulosa cell steroidogenesis in relation to modifications of cell shape. The higher responsiveness of serum cells to gonadotropins makes this model more suitable for physiological and pharmacologic

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80186-8

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summary—Humanα1‐acid glycoprotein (AGP or orosomucoid) is a major glycoprotein of plasma. AGP can be separated on immobilized concanavalin A into three variants bearing none (AGP A), one (AGP B) or two (AGP C) biantennary glycans. In this paper, we show, using flow cytometry and confocal microscopy, that AGP C which is eluted from concanavalin A with mannose, binds to human monocytes, monocyte‐derived macrophages as well as human promonocytic cell lines such as THP1 or U937. Conversely HL60, a promyelocytic cell line, does not express the surface AGP C binding protein. AGP C is internalized and degraded with an efficiency depending on the state of differentiation of these cells. In contrast, AGP A which is not recognized by concanavalin A, does not bind to any of these

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80187-X

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summary—In a previous study, we identified regions on the surface of tumor cells which act as acceptor sites for putrescine (Put) and studied the competition between structural analogs of Put (N,N′‐tetramethyl‐α,ω‐diaminoalkanes) and Put bound to latex microspheres. A chain of four to seven carbons was necessary for inhibition of Put‐latex binding to the cell surface of human glioblastoma (U251) cells. We show here that under the experimental conditions, N,N′‐tetramethyl‐1,4‐butanediamine and N,N′‐tetramethyl‐1,7‐heptanediamine exhibit an antitumor effect. In a first step (1–48 h after treatment), cells exposed to these compounds show large intracellular vacuoles. We failed to detect any acid phosphatase activity in these intracellular structures revealing that they were not lysosomes. Electron microscopy observations argue for the conclusion that these vacuoles are an hypertrophy of the endoplasmic reticulum (ER) and/or of the Golgi vesicles. Our hypothesis is that this typical effect of the analogs reveals that ER could be a physiological target of endogenous polyamines. At a later stage (6 days after treatment), the cells undergo morphological and biochemical changes: thin and long expansions characterize the cells and the GFA protein is overexpressed. Correlated to both these effects, karyotypic modifications are found in chromosomes 3 and 6. These changes evoke a differentiation of the treated cells. The work provides evidence that N‐methylated polyamine analogs taking the place of endogenous putrescine demon

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80188-1

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summary—Aspergillus fumigatus, the causative agent of human aspergillosis, binds to and degrades basement membrane laminin. Using immunoelectron microscopy, laminin binding appeared to be associated with the cell wall expansions of resting conidia, and progressively extended to the outer electron dense layer of the conidial wall during the germination process. Labeling of thin sections revealed numerous binding sites in the cytoplasm, whereas the inner cell wall and the plasma membrane were not labeled. Attachment ofA fumigatusconidia on microtiter plates coated with laminin and its fragments P1 and E8 was also investigated. Conidia cells showed good adhesion to wells coated with laminin. As indicated by inhibition experiments, the interaction was specific and fragment P1 represented the major binding site on the laminin molecule. In addition, sinceA fumigatusproduced an extracellular serine protease, we determined the susceptibility of laminin to this enzyme. We demonstrated that a crude protease extract was capable to degrade laminin in solution as well as in tissue sections. The laminin cleavage products were detected by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. All the three chains were extensively degraded within 1 h. Treatment of the crude protease extract with the enzyme inhibitors, phenylmethylsulfonyl‐fluoride and chymostatin, blocked the degradation of laminin, indicating a chymotrypsin‐like serine protease activity. Immunofluorescence microscopy of cryostat sections of mouse and rat kidneys treated with the protease extract showed widespread loss of laminin epitopes from basement membranes. Enzyme treatment also removed immunoreactivity from lungs as observed after immunoperoxidase performed on paraffin sections. Binding and proteolytic degradation of laminin may together facilitate initial interaction ofA fumigatuswith the host

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80189-3

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Summary—The attachment ofPneumocystis cariniito lung cells could play a role in the pathophysiology ofP cariniipneumonia. The trophozoite attaches to type I alveolar epithelial cells. Physical, chemical, and extracellular matrix factors, involved in the mouseor rat‐derivedP cariniiattachment to fibroblastic cells in culture, were examined using a new model ofin vitroadherence. The development of parasite filopodia penetrating deeply the host cell cytoplasm was observed using transmission electronic microscopy. KilledP cariniiorganisms were unable to attach to cultured cells. Also, parasites were unable to attach to killed target cells. TheP carinii in vitroattachment was partially inhibited by cytochalasin B. In contrast, the parasite attachment was not affected when the target cell cytoskeleton was altered. In our work conditions, sialic acids were not involved in the attachment process. Present results showed that fibronectin (Fn) plays a role in the parasite attachment, and suggest that a specific Fn‐binding receptor is present at the surface of mouse‐derivedP cariniior

ISSN:0248-4900    

DOI:10.1016/S0248-4900(05)80190-X

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY