摘要:

AbstractA lysed cell system was used to study the organelle structure and nucleation of exogenous tubulin at kinetochores and centrosomes in mitotic PtK2cells. We have used this lysed cell system in conjunction with nuclease digestion experiments to determine which specific nucleic acids (DNA or RNA) are involved in either the structure and/or microtubule‐initiating capacity of kinetochores and centrosomes. The results indicate that DNase I specifically decondenses the kinetochore plate structure, with the eventual loss in the ability of the chromosomes to nucleate microtubule assembly. DNase I had no effect on either the structure or nucleating capacity of centrosomes. Both RNase T1and RNase A specifically attacked the amorphous pericentriolar material of the centrosomes, with a concomitant loss in the ability of this material to nucleate microtubule formation. Neither RNase appeared to affect the structure or nucleating capacity of the kinetochore. Therefore, the two types of nucleases appear to exert preferential effects on the different types of microtubule initiation sites in mitotic mammalian cells. The results suggest that DNA is a major component of the kinetochore, while RNA is a major component of the amorphous pericentriolar material. These findings support the concept that microtubule initiation sites in mitotic cells contain nucleic acids which are essential for the structural and functional integrity of the site

ISSN:0271-6585    

DOI:10.1002/cm.970010102

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

年代:1980

数据来源: WILEY

摘要:

AbstractColonies of Labyrinthula, a colonial marine protist, expand by protrusive movements of the specialized slimeways. The movements recorded in time‐lapse films are of two types – filopodial and lamellipodial – and occur at rates equivalent to those of cell translocation.Evidence is presented that Ca2+regulates the contraction of the actomyosin system of filaments present in the slimeways of Labyrinthula. In glycerinated models or in colonies exposed to ionophore A23187 contraction is evidenced by the occurrence of periodic contractions of the slimeways, giving them the appearance of strings of beads. Glycerinated slimeways contract on the addition of Ca2+and ATP while slimeways provided with ionophore A23187 contract on addition of Ca2+alone. The concentration required is 1.1 × 10−7M Ca2+while concentrations of 6.2 × 10−8or lower were ineffective. Rates of contraction were measured in time‐lapse films which provide evidence that contractions and beading occur everywhere in the slimeway system. When beading occurs, the 6‐nm filaments transform from an array of parallel single filaments into an interwoven meshwork.We have identified by pyroantimonate‐OsO4fixation, as possible Ca2+reservoirs, deposits of Ca2+in bothrosomes – structures through which cell secretions pass into the slimeways. The electron‐dense deposits are located at the base of the bothrosome and disappear after incubation with EGTA. We propose that the translocation of cells as well as the movements of slimeways may be regulated by the cells through the local measured liberation of Ca2+from the bothrosome wh

ISSN:0271-6585    

DOI:10.1002/cm.970010103

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

年代:1980

数据来源: WILEY

摘要:

AbstractFollowing fertilization, the sea urchin egg cortex undergoes a structural change involving the assembly and organization of actin filaments into microvilli. Antifascin localizes this actin cross‐linking protein in the microvilli of the fertilized egg cortex but no organized staining is present in the unfertilized cortex. Determination of the actin content of eggs using the DNAase I inhibition assay indicates that actin is about 1.4% of the total protein. Approximately 90% of this actin is soluble in low calcium isotonic extracts of unfertilized eggs while only 60–65% can be recovered in identical extracts of fertilized eggs. Similar measurements for fascin using a radioimmunoassay indicate this molecule represents about 0.3% of the total egg protein, essentially all of which is recovered in low calcium isotonic extracts of unfertilized eggs. After fertilization only 65–70% of this actin cross‐linking protein is in the soluble phase. These results demonstrate a markedly different solubility for actin and fascin after fertilization, when the indirect immunofluorescence staining localizes fascin in the microvilli, and are consistent with the idea that fascin organizes newly polymerized actin filaments into the microvillar cores. A consideration of the amounts of actin and fascin incorporated into the cortex after fertilization and the number of microvilli on the egg surface indicates that the measured values are sufficient to account for the observed microvillar elo

ISSN:0271-6585    

DOI:10.1002/cm.970010104

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

年代:1980

数据来源: WILEY

摘要:

AbstractMitotic micronuclei were isolated from Tetrahymena thermophila and data on spindle ultrastructure were obtained from serial, transverse sections. Comparison of data from nuclei at meta‐ and early anaphase with data from nuclei at late anaphase showed that during anaphase, sister kinetochores move from the equator to the spindle poles, but kinetochore translocation occurs without any apparent change in either the number or length of kinetochore microtubules. This unprecedented result is ascribed significance with regard to the mechanism of kinetochore transport since there are only a limited number of ways that result could be achieved. The organization of the peripheral sheath changes during anaphase as evidenced by gaps in the sheath at late anaphase. Numerous kinetochore and non‐kinetochore microtubules are located in polar regions of the spindle at late anaphase, whereas those regions contained only peripherally arranged microtubules at earlier stages. Tracking of individual kinetochore microtubules in late anaphase nuclei showed that some of them appeared to become incorporated into the peripheral sheath near the pole. At early and late anaphase, crossbridges connect adjacent microtubules throughout the spindle poleward to the kinetochores, as well as in the interz

ISSN:0271-6585    

DOI:10.1002/cm.970010105

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

年代:1980

数据来源: WILEY

摘要:

AbstractMyosin from the slime mold Physarum polycephalum contains three sizes of polypeptides: a heavy chain and two light chains, LC‐1 and LC‐2. Using a simple qualitative test for calcium binding by comparing electrophoretic migration of the polypeptides in sodium dodecy1 sulfate (SDS) acrylamide gels in the presence and absence of calcium, we have found that Physarum myosin light chain LC‐2 migrates with an apparent molecular weight of 16,900 daltons in the presence of the metal ion chelator ethylene glycol bis (B‐aminoethyl ether) N,N′‐tetraacetic acid (EGTA). However, if calcium chloride is added to the sample prior to electrophoresis, the apparent molecular weight decreases to 16,100. Lanthanide and cadmium ions, but not magnesium, can substitute for calcium. Because the ionic radii of Ca2+, La3+, and Cd2+are almost identical, we conclude that Physarum myosin LC‐2 possesses a very size‐specific binding site for calcium. Physarum myosin LC‐1 and the heavy chain give no evidence for binding calcium by this test. Since cytoplasmic streaming in the plasmodium of Physarum requires calcium, our evidence indicates that the calcium‐binding property of Physarum myosin LC‐2 may be important in regulating the production of force by actomyosin in the ectoplasm. Unexpectedly, the myosin light chain in Physarum capable of binding calcium, LC‐2, is the essential light chain, while LC‐1 is a member of the regulatory class of myosin light chains [V. T. Nachmias, personal communication]. Until now, essential myosin light chains have not been shown to have high affinity divalent cation binding sites. This means a new version of the myosin‐based model for actomyosin regulation by calcium may be required to explain cytoplasmic movement in Physarum, and perhaps in other motile systems involving

ISSN:0271-6585    

DOI:10.1002/cm.970010106

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

年代:1980

数据来源: WILEY

摘要:

AbstractA search for new mutants with altered body‐wall muscle cell structure has been undertaken in the nematode C elegans. One‐hundred seventeen mutants were isolated after mutagenesis with ethyl methanesulfonate or ultraviolet light, enrichment by a motility‐requiring test, and screening by polarized light microscopy; 102 of these mutants were in ten previously established genes, whereas 15 mutants permitted the identification of seven new complementation groups in C elegans. Two of the new genes map on linkage group I (unc‐94andunc‐95) and four genes are sex linked (unc‐96, unc‐97, unc‐98, andunc‐99). One complementation group (unc‐100) could not be mapped because of the special characteristics of its cohort mutants. Representative mutants of the mapped genes were examined by polarized light and electron microscopy. All of the mutants exhibit disruptions of the normal A and I band organization of thick and thin filaments. Several of the mutants produce collections of thin filament‐like structures. In one of these cases, HE177 demonstrated collections of somewhat wider, intermediate‐sized filaments as well, and the HE195 mutant produces paracrystalline aggregates of thin filaments amidst looser arrangements of similar structures. The mutants in newly identified genes, as well as the new mutants in previously established genetic loci, have promise as tools in the study of myofibrillar assembly and function. Among the 22 complementation groups associated with body‐wall structure in C elegans, it is likely that some genes code for regulatory and morphogenetic functions in addition to the well‐studied structural, contractile, and calcium‐

ISSN:0271-6585    

DOI:10.1002/cm.970010107

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe effect of specific components of the extracellular matrix on the motility of tissue cells was studied using organ‐cultured aggregates of embryonic fibroblasts. Spherical aggregates of chick embryo heart and skin fibroblasts were fused with [3H]‐thymidine‐labeled aggregates of the identical cell type. The movement of labeled cells into the unlabeled partner aggregate served as an estimate of cell motility in the cultured tissue‐like aggregates. Collagenase treatment decreased the collagen content of heart fibroblast aggregates and increased cell motility; ascorbic acid treatment increased the collagen content of skin fibroblast aggregates and decreased cell motility. Reduction of the glycosaminoglycan content with testicular hyaluronidase had no measurable effect on cell motility in heart fibroblast agg

ISSN:0271-6585    

DOI:10.1002/cm.970010108

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

年代:1980

数据来源: WILEY

摘要:

AbstractDrosophila Kc cells exposed to physiological doses of the moulting hormone, β‐ecdysone, elongate, become motile, and subsequently aggregate. This pattern of morphogenesis was found to require the assembly of a microtubular cytoskeleton. Tubulin content was significantly increased in hormone‐treated cells when compared to controls, as measured by a3H‐colchicine‐binding assay. However, determinations of rates of tubulin synthesis and breakdown revealed no difference between control and hormone‐treated cells for either parameter. When tubulin content was assayed by methods that do not depend on colchicine‐binding activity, no difference between hormone‐treated and control cells was observed. These results are discussed in terms of a model in which β‐ecdysone affects the distribution of tubulin in “assembly‐active” and

ISSN:0271-6585    

DOI:10.1002/cm.970010109

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

年代:1980

数据来源: WILEY

摘要:

AbstractSea urchin coelomocytes were examined during their morphological transformation from petaloid to filopodial forms by scanning electron microscopy and ciné film analysis. Petaloid coelomocytes have a variable morphology but, in general, consist of numerous thin sheets of cytoplasm, the petals, arranged in three dimensions around a central nuclear region. The transition to the filopodial form can occur in either substrate‐attached or suspended cells and begins with the formation of several microspikes at the edge of each petal. These become more apparent as the cytoplasm between each microspike/filopodium is retracted centripetally. Concomitantly, the diameter of the flattened cell is increased by as much as twofold as the filopodia actively lengthen at a uniform, average rate of 0.5 μm/minute. The transformation process requiresca15 minutes and is complete when the cell diameter no longer increases. These filopodia are functionally distinct from the passively produced retraction fibers observed in cultured mammalian cells. The formation of filopodia is biphasic and includes both a cytoplasmic retraction phase and an active extension ph

ISSN:0271-6585    

DOI:10.1002/cm.970010110

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

年代:1980

数据来源: WILEY

摘要:

AbstractIn multicellular organisms, guidance cues are either diffusible molecules or cellular or extracellular surfaces that are found in reproducible locations and that orient migrating cells and cell processes. The pattern of the guidance cues usually determines the complex in vivo migration routes of motile cells and cell processes. Within organisms, guidance cues are found to be organized in two general patterns: (a) broad gradients ‐ such as diffuse chemotactic gradients; (b) discrete routes (substrate pathways) ‐ such as chemotactic gradients confined to long channels, and such as the axon surface which represents a long specific highway for migrating Schwann ce

ISSN:0271-6585    

DOI:10.1002/cm.970010111

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

年代:1980

数据来源: WILEY