摘要:

AbstractAvian muscular dystrophy is characterized by the degeneration of fast white skeletal muscle fibers, with onset during development. Using a one‐dimensional peptide mapping technique, we have detected two forms of the myosin heavy chain in the fast white fibers of adult domestic chickens, one form characteristic of birds homozygous for muscular dystrophy, the other of their normal controls. Four dystrophic strains carrying the same gene for muscular dystrophy were examined.No differences were detected in the embryonic heavy chain peptide maps of normal and dystrophic chickens, consistent with the developmental onset of the condition. Differences were also absent from the peptide maps of heavy chains from slow red fibers, which are unaffected in dystrophy. No dystrophy‐specific peptide map differences were detected in the three light chains. Analysis of peptide maps of rod and the heavy chain component of subfragment‐1 from normal and dystrophic heavy chains indicates the presence of amino acid sequence differences in the two pro

ISSN:0271-6585    

DOI:10.1002/cm.970010402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractI have used fluorescence microscopy and antibodies to 10nm filaments and tubulin labelled with contrasting fluorochromes to compare the distribution of these proteins in endothelial cells during cell division. During interphase the two filament systems have entirely different distributions: The bulk of the 10nm filaments form a ring that surrounds the cell center and nucleus and remains parallel to the substrate, while the microtubules radiate from the cell center to the cell's border. When the mitotic spindle replaces the radial microtubule pattern in mitosis, the spindle poles remain within—and in close proximity to—the ring of 10nm filaments. This was confirmed by electron microscopy which showed the ring and centrioles in the same plane separated by a distance of 300–4

ISSN:0271-6585    

DOI:10.1002/cm.970010403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractCalcium is now generally thought to play a key role in regulating a variety of cellular movements. When the plasmodium of Physarum polycephalum was treated with the calcium‐ionophore A23187 or the quasi‐ionophore amphotericin B, Ca2+leaked out. Ca2+efflux into the ambient solution from the plasmodial strand segment was measured by the luminescence of a photoprotein aequorin, and the tensile force production was recorded simultaneously. Ca2+efflux oscillated with the same period as the cycle of tension generation in the strand, but the phase of cyclic changes in Ca2+efflux was opposite to that of tension generation. That is, Ca2+efflux fell in the increasing tension phase and rose in the decreasing tension phase. Cyclic changes in efflux of Ca2+are provisionally interpreted as reflecting corresponding changes in concentrations of free Ca2+in the cytopl

ISSN:0271-6585    

DOI:10.1002/cm.970010404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractDissociated bovine brain microtubule protein has been shown to reassemble at 0°C in the presence of the drug taxol. Tubulin polymerization was monitored both by electron microscopy of the polymeric structures and by incorporation of tritiated GTP into filterable polymeric structures. Most of the labeled guanine nucleotide uptake into tubulin polymeric structures occurred in the first 30 minutes of incubation with the drug. The initial polymerization event results in the formation of protofilamentous tubulin ribbons. The first microtubules were noted after 1 hour of incubation with the drug. After 20 hours of incubation at 0°C with taxol, the bulk of the polymerized tubulin appeared to be in the form of microtubules. Cold‐stable tubulin rings with a mean diameter of 34 nm were present in the reaction mixture before the addition of taxol and throughout the 20‐hour incubation. Most of the rings were apparantly not involved in the taxol‐induced microtubule assembly. The results are consistant with a model whereby taxol induces an initial formation of protofilamentous ribbon structures, mostly from free tubulin dimers, and a slower subsequent folding of the ribbon structures into micro

ISSN:0271-6585    

DOI:10.1002/cm.970010405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractIncomplete cytokinesis followed by the disappearance of the midbody and spindle remnant results in intercellular bridges between the cells of the blastoderm of the squid embryo. An electron microscope study of the morphology of the stages of development of the intercellular bridge is presented. Cytokinesis ceased as the furrow base reached a diameter slightly larger than the midbody. As furrowing stopped, a dense material accumulated to form a cylindrical sheath 50 nm thick, lining the inner surface of the furrow base. Proteolytic enzymes showed this material to have a significant protein component. As the midbody broke down, vesicles lined the inner surface of the bridge sheath. In this configuration, there was cyto‐plasmic continuity between the cells, and organelles appeared to pass through the bridge.The intercellular bridge could become temporarily closed. Vesicles entered the channel and fused with the vesicles lining the inner surface of the sheath. The vesicles enlarged until the channel became occluded with a series of transverse cisternae, the edges of which were embedded in the material of the sheath. When the bridge reopened, the transverse cisterna appeared to dissociate from the sheath, move out of the channel, and break down. Occasionally bridges were seen in which the bridge wall appeared distorted into lobes. It is suggested that such bridges might be in the porcess of breaking down, resulting in the final separation of the cell

ISSN:0271-6585    

DOI:10.1002/cm.970010406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractThe reassembly of microtubules is described in mitotic cells after release from nocodazole‐induced block. The formation of microtubules was followed by light microscopic immunocytochemical staining using the PAP method, combined with to‐luidine blue staining of the chromatin. The light microscopic observations on whole cells were compared with ultrastructural observations on thin sections. This step is essential to ascertain complete destruction of microtubules during the nocodazole treatment and to correlate immunocytochemical staining with the presence of microtubules.Removal of nocodazole (10 or 1 μg/ml) after a sufficiently long incubation to induce a complete disappearance of microtubules resulted in the appearance of tubulin staining specifically associated with the centromeres and with one or two isolated points in the cytoplasm. Electron microscopy confirmed that the staining was due to the massive accumulation of small microtubules at the kinetochores and centrosomes. Kinetochore nucleation was seen only in association with condensed metaphase‐stage chromosomes and not with the less‐condensed prophase chromosomes.In a second type of experiment cells were allowed to enter mitosis in the presence of an incompletely active concentration of nocodazole (0.1 μg/ml). The construction of the mitotic spindle was arrested; however, short microtubules were assembled at the kinetochores and centrosomes.These experiments demonstrate that in living mitotic PTK2cells the kinetochores, as well as the centrosomes, exert a nucleating action on tubulin assembly.The further elongation of microtubules after removal of nocodazole was seen to occur preferentially along axes between the centrosomes and the kinetochores. This resulted in the construction of normal metaphases that evolved through anaphase and telophase. We have attempted to formulate a hypothesis that may explain the oriented assembly that seems to be essential in the construction of th

ISSN:0271-6585    

DOI:10.1002/cm.970010407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractBoth actin and tubulin, the major proteins of the cytoskeleton, bind nucleotide triphosphate (NTP) and exhibit the phenomenon of “polymerization‐coupled” NTP hydrolysis. In this report I review the nature of polymerization‐coupled NTP hydrolysis, and its possible role in the cellular function of actin and tubulin. Polymerization‐coupled hydrolysis may be viewed as simply reflecting differences in the NTPase activity of free subunit as compared to polymer. Making assumptions concerning the values of various rate constants, it is possible to write expressions for the effects of NTP hydrolysis on the kinetics of polymerization. The role of NTP hydrolysis may be viewed in at least three different ways: (1) Hydrolysis alters the kinetics of assembly and disassembly. This leads to a consideration of the role of subunit flow in microtubule and microfilament function. (2) Hydrolysis is an essentially irreversible step that separates the assembly and disassembly reactions. This suggests a role of NTP in the regulation of polymer content during cellular cycles of assembly and disassembly. (3) NTP may allow transient stabilization of intersubunit bonds. This suggests a role of NTP in nucleation and possible regulation of nonequilibrium states of

ISSN:0271-6585    

DOI:10.1002/cm.970010408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractMicrotubule‐associated proteins (MAPs), isolated from brain tubulin, bound to and saturated outer fibers of Chlamydomonas flagella. MAPs present on these microtubules prevented the subsequent recombination of dynein. MAPs also bound to intact axonemes and thus did not specifically bind to the dynein binding sites on the A subfiber. A molar ratio of 1 mole MAP2per 27 moles tubulin dimers at saturation of the outer fibers with MAP2suggested that MAPs could effectively interfere with dynein recombination only if the MAPs were near the dynein binding sites to sterically prevent binding. However, electron microscopic observations indicated that MAPs were not localized but, instead, were dispersed around the outer fibers. In addition, MAP2present at saturating amounts on in vitro assembled brain microtubules had no significant effect on dynein binding. Dynein‐decorated microtubules contained clusters of arms suggesting that there may be cooperative interaction between the arms during dynein binding. Because the A subfiber of axonemes contains sites to which dynein preferentially attaches, MAPs may prevent recombination by interfering with cooperative binding to these specific sites. Dynein presumably binds with equal affinity to any protofilament on in vitro assembled microtubules, and, therefore, the MAPs may not be capable of effectively interfering with cooperative binding of dynein to these microtubu

ISSN:0271-6585    

DOI:10.1002/cm.970010409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

ISSN:0271-6585    

DOI:10.1002/cm.970010401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY