摘要:

Summry—The new data presented by the participants during the ‘Colloquium on the Nucleolus’ were reviewed and regrouped in different topics concerning the molecular and functional significance of nucleolar structure. The topics included: rRNA transcription and nucleolar organization, the nucleolus in relation to cell proliferation including nucleolus in pathology during the cell cycle and cell division, nucleologenesis, and nucleolar pro

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86824-4

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—Structural investigations on the chitin secretion system of a deep‐sea hydrothermal vent tubeworm,Riftia pachyptila, are presented. In this organism, 300‐nm cup‐shaped organelles are responsible for the formation of large (50 nm) crystalline chitin microfibrils of the rare β form. Electron tomographic reconstructions of plastic‐embedded cup‐shaped organelles were carried out, using 93 projections distributed over a ± 70° angular range with a 0.63‐nm pixel size. In addition, the shrinkage profile of the plastic sections was measured to determine the required imaging conditions. The entire data collection was done automatically and carried out under cryo‐conditions. Automation resulted in an efficient use of irradiation dose; 96% of the total dose is required for the data itself, only 4% is used for the required compensation of focus change and image shift. The results are presented as 3‐nm thick slices through the 3‐D reconstruction, (parallel to the original thin section,iethe x‐y plane). The 3‐nm slices allow to visualize separate structures that are overlapping in a conventional 2‐D projection of the initial thin section. Also, these thin slices through the 3‐D reconstruction show the fine contours of the nascent microfibril tip, w

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86825-6

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—In the course of the apoptotic cell death, cells fragment into apoptotic bodies, the elimination of which by phagocytosis is thought to avoid the release of cytosolic constituents whose occurrence is indicative for necrotic cell death. Confluent cultures of chicken embryo fibroblasts, however, show a different behaviour. After serum deprivation, they transiently released with the same time course mitogenic activity, lactate dehydrogenase and cytosolic peptidyl prolylcis‐transisomerases into the serum‐free culture medium. The release correlated in time with a decrease of the cell number which started ∼3 h after serum removal and ceased within ∼10 h at about half of the initial cell density. Morphological features like cell shrinkage, membrane blebbing and cell fragmentation as well as internucleosomal DNA fragmentation indicated apoptotic cell death whereas necrotic cell death could be excluded. Conditioned medium (Mr≥ 30 kDa) from serum‐deprived cultures of chicken embryo fibroblasts completely prevented chicken embryo fibroblasts to undergo apoptosis as did phorbol 12‐myristate, 13‐acetate and, to ∼60%, L‐cysteine. Cycloheximide had no effect on serum deprivation‐induced apoptosis. From the present results it can be concluded that chicken embryo fibroblasts and possibly other cells undergoing apoptosis release cytosolic components and endogenous survival factor(s)

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86826-8

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—Before fertilization, capacitation and the acrosome reaction in mammalian spermatozoa must be completed. The motility and fertility of hamster sperm were examined in four kinds of modified Tyrode's solution with or without bovine serum albumin (BSA). Since the presence or absence of polyvinylalcohol (PVA) in the media was another variable, its effect on the sperm motility and fertility was also studied. Sperm were incubated in four different media for up to 6 h at 37.5°C. After 4 h of incubation in the media containing BSA alone or BSA and PVA, sperm were hyperactivated, showing a high sperm motility index (SMI) and were able to fertilize more than 80% of eggs. However, their fertility rapidly decreased during further incubation. In contrast, sperm in the medium containing PVA and no BSA showed low SMI scores after 4 h. However, during the following 2‐h period, the SMI progres‐sively increased and sperm were hyperactivated. Furthermore, the hyperactivated sperm in the PVA containing medium were able to effectively fertilize eggs. Our results indicate that hamster sperm can be capacitated in BSA‐free medium and that capacitation occurs much more slowly in such a medium. We suggest that PVA is a reasonable alternative to BSA inin vitrofertilization and that this slowly progressing system may be a good model for studying various steps in sperm ac

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86827-X

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—The flagellate form ofTrichomonas vaginalis(Tv) transforms to amoeboid cells upon adherence to coverslips. They grow and their nuclei divide without undergoing cytokinesis, yielding giant cells and a monolayer ofTvF‐actin was demonstrated inTrichomonas vaginalisby fluorescence microscopy using phalloidin and an anti‐actin mAb which labelled the cytoplasm of both the flagellate and amoeboid forms. Comparative electrophoresis and immunoblotting established that the actin band has the same 42 kDa as muscle actin, but 2‐D electrophoresis resolved the actin band into four spots; the two major spots observed were superimposable with major muscle actin isoforms. Electron microscopy demonstrated an ectoplasmic microfibrillar layer along the adhesion zone of amoeboidTvadhering to coverslips. Immunogold staining, using anti‐actin monoclonal antibodies demonstrated that this layer was mainly composed of actin microfilaments. A comparative immunoblotting study comprising seven trichomonad species showed that all trichomonads studied expressed actin. The mAb Sigma A‐4700 specific for an epitope on the actin C‐terminal sequence labelled only actin ofTrichomonas vaginalis, Tetratrichomonas gallinarum, Trichomitus batrachorumandHypotrichomonas acosta, but not the actin ofTritrichomonas foetus, Tritrichomonas augustaandMonocercomonassp. This discrimination between a ‘trichomonas branch’ and a ‘tritrichomonas branch’ is congruent with inferred sequence phylogeny from SSu rRNA and with classical phyl

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86828-1

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—Basement membrane structures, or their main component, type IV collagen, have been detected in all multicellular animal species, except sponges. We cancel this exception by the demonstration of type IV collagenous sequences in a new marine sponge species by cDNA and genomic DNA studies. One of these sequences is long enough to demonstrate the specific characteristics of type IV collagen chains. The 12 cysteines are at conserved positions in the carboxyl‐terminal non‐helical NC1 domain, as are the interruptions in the carboxyl‐terminal end of the triple helical domain. The gene organization of the region coding for the NC1 domain is similar to that of the human genesCOL4A2, COL4A4andCOL4A6. An additional, shorter sequence suggests the presence of a second chain. The expected tissue localization of this collagen has been confirmed using polyclonal antibodies raised against a sponge recombinant protein. These results demonstrate that type IV collagen is representated in all animal phyla. It is actually the only known ubiquitous collagen and it has at least two different alpha chains in all the species where it has been charac

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86829-3

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—Protein tyrosine kinases play important roles in the development of the mammalian nervous system during embryogenesis and in the maintenance of function of the adult brain. Using a semi‐nested PCR technique based on a short amino acid motif of protein tyrosine kinases, we isolated a human genomic DNA encoding a peptide whose sequence was related to known mammalian protein tyrosine kinases. The expression was examined by Northern blot analysis, and transcripts were detected almost exclusively in the brain. The corresponding cDNA was sequenced, and it was revealed that the gene designated asbykcoded for a receptor‐like molecule with a motif of protein tyrosine kinase. Immunohistochemical analysis demonstrated that the Byk protein was expressed in neurons and was located in the nuclear envelope. To understand the physiological significance of the Byk protein, we investigated the behavior of this molecule in the hippocampus after ischemia. Byk‐like immunoreactivity disappeared from the neurons in the fields CA1 through CA3 and the dentate gurus of the hippocampus following 20 min of ischemia. After recirculation of blood flow, neurons in the CA3 field and the dentate gyrus re‐expressed Byk‐like antigen but CA1 neurons did not. Interestingly, Byk‐like immunoreactivity was detected in microglial cells and astrocytes in the CA1 field that were activated after ischemia. Byk could be a new tool to study the neuron‐glia and glia‐

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86830-X

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summry—Synaptotagmins are a family of calcium‐ and phospholipid‐binding proteins implicated in the function of cell exocytosis. Synaptotagmins I and II are neurally expressed proteins thought to be involved in neurotransmitter release from neurons. We have expressed rat synaptotagmin II in severalSaccharomyces cerevisiaetemperature‐sensitive secretory mutants that are defective in Golgi to plasma membrane vesicular transport. Synaptotagmin II expression was able to partially rescue the growth defect in one particular mutant,sec15. No suppression was observed when synaptotagmin II was expressed insec1, sec2, sec4, sec5, sec6, sec8, sec9, sec14, sec17, orsec18. Two synaptotagmin II deletion mutants were also expressed insec15and screened for suppression. The expression of the cytoplasmic domain of synaptotagmin alone was not able to suppress thesec15growth defect. In addition, the expression of a synaptotagmin II fragment lacking the second half of the cytoplasmic domain including the second C2 domain did not suppresssec15. We have isolated a membrane fraction enriched in post‐Golgi vesicles from asec15strain expressing synaptotagmin II and found that synaptotagmin II co‐purifies with this fraction, suggesting that the rat synaptotagmin II is targeted to membranes in yeast. Sec 15p forms a large multisubunit protein complex that includes Sec6p and Sec8p. This protein complex is thought to function in a late stage of exocytosis in yeast. Sec6p and Sec8p homologs have been identified in mammalian cells. Our studies suggest that synaptotagmin may be a part of this complex or regulate its function in mamm

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86831-1

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86835-9

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0248-4900    

DOI:10.1016/S0248-4900(97)86837-2

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY