摘要:

AbstractThe biflagellate green algaSpermatozopsis similisexhibits a remarkable avoidance reaction in addition to the photophobic or stop response characteristic of such algae.S. similisnormally swims forward with its anteriorly attached flagella directed posteriorly and propagating sine‐like waves from base to tip. Upon contact with surfaces or other cells,S. similisresponds with rapid backward swimming, covering distances of up to 50 μm in 140 to 220 msec. This reaction, which we term the mechanoshock response, also can be triggered by vigorous mechanical stimulation, but not by physiological light intensities. It consists of 3 phases: (1) a rapid acceleration phase with average duration of 31 msec; (2) a phase of about 66 msec with constant high speed (maximal velocities of>600 μm·sec−1) or slow deceleration; and (3) a deceleration phase of ∼ 83 msec, followed by a stop or short period of circling. The cells then resume forward swimming in a random direction. Prior to the mechanoshock response the flagella rapidly are brought together into a close parallel configuration extending anteriorly of the cell body. They then appear to propel the cell by undulatory beating, while the cell describes a pronounced helical path. Small decreases in the extracellular Ca2+concentration, as well as low concentrations of Ba2+, strongly suppress the probability of this phobic reaction. We conclude that this mechanoshock response involves large Ca2+influxes, probably mediated by mechanosensitive and/or stretch‐activated ion‐channel(s). © 1994 Wi

ISSN:0886-1544    

DOI:10.1002/cm.970290202

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

年代:1994

数据来源: WILEY

摘要:

AbstractHigh molecular weight microtubule‐associated proteins MAP1A and MAP2 form thin projections from microtubule surfaces and have been implicated in crosslinking microtubules and other cytoskeletal components. We have purified native MAP1A from bovine brain and have studied its interaction with G‐ and F‐actin. Using a solid‐phase immunoassay we show that MAP1A binds in a dose‐dependent manner to both G‐actin and F‐actin. Addition of MAP1A to F‐actin causes gelation of F‐actin and SDS‐PAGE analysis shows that MAP1A co‐sediments with the gelled network, under conditions where F‐actin alone does not pellet. The low apparent viscosity of F‐actin is markedly increased in the presence of MAP1A, suggesting that MAP1A can crosslink F‐actin. Co‐incubation experiments indicate that MAP1A and MAP2 may bind to common or overlapping sites on the actin molecule. The widespread distribution of MAP1A and its interaction with microtubules, actin, and intermediate filaments suggests that it may constitute an important determinant of neuronal and non‐neuronal cellular mor

ISSN:0886-1544    

DOI:10.1002/cm.970290203

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe report here a novel intracellular localization and function of Tau proteins in cultured cerebellar neurons. Immunofluorescence staining of detergent‐extracted cytoskeletons with antibodies specific for Tau proteins revealed intense labeling of growth cone microtubules. Besides, suppression of Tau by antisense oligonucleotide treatment results in the complete disappearance of antigen 13H9, a specific growth cone component with properties of microfilament‐ and microtubule‐associated protein [Goslin et al., 1989:J. Cell Biol.109:1621–1631], from its normal intracellular location. This phenomenon is unique to neurite‐bearing cells, is not associated with the disappearance of microtubules from growth cones, and is not reversed by taxol, a microtubule‐stabilizing agent. In addition, Tau‐suppressed neurons display a significant reduction in growth cone area and fillopodial number; on the contrary, fillopodial length increases significantly. The alterations in growth cone morphology are accompanied by considerable changes in the phalloidin staining of assembled actin. Taken together, the present results suggest that in developing neurons Tau proteins participate in mediating interactions between elements of the growth cone cytoskeleton important for maintaining the normal structural organization of this neuritic domain. © 1994 W

ISSN:0886-1544    

DOI:10.1002/cm.970290204

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe effects of 6‐dimethylaminopurine (6‐DMAP) on the length of the cell cycle and on the state of phosphorylation of a putative intermediate filament protein, p117, have been studied in sea urchin embryos. Embryos were transferred into sea water containing 600 μM 6‐DMAP at 0.5, 2 or 5 min after insemination, and incubated for 30 or 90 min. The effects of 6‐DMAP on cell cycle length were studied by determining the time required for completion of mitosis upon return of the embryos in normal sea water. In all instances, except for the embryos transferred 0.5 min after insemination (AI) and incubated for 30 min, the duration of the M phase was shortened compared to controls, being faster in the embryos incubated for 90 minutes compared to the 30 min incubation period. However, embryos transferred 0.5 min AI have a longer M‐phase than those transferred 2 minutes or later after fertilization, suggesting that between 0.5 and 2 min after fertilization, critical phosphorylating events occur which affect the commitment of the cells to enter M‐phase.To study the pattern of p117 phosphorylation during the cell cycle, the eggs were transferred 2 minutes after fertilization in presence of 600 μM 6‐DMAP and with 200 μCi/ml of32P‐orthophosphate. Analyses of32P‐labelled proteins after exposure of SDS‐PAGE gels and their corresponding blots suggested that phosphorylation of p117 greatly increases at the time of pronuclear fusion, and then declines slightly at prophase‐metaphase. This decrease is markedly enhanced when the cells are treated with 6‐DMAP during metaphase in order to induce a premature breakdown of the mitotic apparatus. A causal link is suggested between the level of phosphorylation of p117 and its state of assemb

ISSN:0886-1544    

DOI:10.1002/cm.970290205

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

年代:1994

数据来源: WILEY

摘要:

AbstractCiliary and flagellar motion is driven by the dynein‐tubulin interaction between adjacent doublets of the axoneme, and the resulting sliding displacements are converted into axonemal bends that are propagated. When the axoneme is bent in the normal beating plane, force develops across the axoneme in the plane of the bend. This transverse force (t‐force) has maximal effect on the interdoublet spacing of outer doublets 2–4 on one side of the axoneme and doublets 7–9 on the opposite side. Episodes of sliding originates as the t‐force brings these doublets into closer proximity (allowing dynein bridges to form) and are terminated when these doublets are separated from each other by the t‐force. A second factor, the adhesive force of the dynein‐tubulin attachments (bridges), also acts to pull neighboring doublets closer together. This force resists termination of a sliding episode once initiated, and acts locally to give the population of dynein bridges a type of excitability. In other words, as bridges form, the probability of nearby bridges attaching is increased by a positive feedback exerted through the interdoublet spacing. A conceptual working hypothesis explaining the behavior of cilia and flagella is proposed based on the above concepts. Additionally, the feasibility of this proposed mechanism is demonstrated using a computer simulation. The simulation uses a Monte Carlo‐type algorithm for dynein attachment and adhesive force, together with a geometric evaluation of the t‐force on the key microtubule pairs. This model successfully develops spontaneous oscillations from any starting configuration (including a straight position). It is compatible with the physical dimensions, mechanical properties and bridge forces measured in real cilia and flagella. In operation, it exhibits many of the observed actions of cilia and flagella, most notably wave propagation and the ability to produce both cilia‐like and flagella‐like waveforms.

ISSN:0886-1544    

DOI:10.1002/cm.970290206

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

年代:1994

数据来源: WILEY

摘要:

AbstractA 100‐kDa polypeptide with microtubule‐interacting properties was identified in a Golgi vesicle‐enriched fraction fromCorylus avellanapollen. The k71s23 antibody (directed to the kinesin heavy chain from bovine brain) [Tiezzi et al., 1992:Cell Motil. Cytoskeleton21:132–137] localized the polypeptide on the external surface of membrane‐bounded organelles. Some 100‐kDa‐containing vesicles co‐pelleted with microtubules (polymerized from purified bovine brain tubulin) either in presence or absence of 5 mM AMPPNP, but they could be released by 10 mM ATP or 0.5 M KCl. The pollen microtubule‐interacting protein, salt‐extracted from membranes and partially purified by gel filtration, exhibited an ATPase activity (16.2 nmolPi/mg/min) which could be stimulated about 2‐fold (32.5 nmolPi/mg/min) by addition of bovine brain microtubules. We suppose that the 100‐kDa polypeptide is part of a molecular complex showing properties of the kinesin class.

ISSN:0886-1544    

DOI:10.1002/cm.970290207

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

年代:1994

数据来源: WILEY

摘要:

AbstractUsing a monoclonal antibody 2D3 generated against a kinetochore‐enriched human chromosome preparation, we identified a high molecular mass protein with nuclear staining in interphase and polar staining of the pericentriolar region in the mitotic spindle. Initially termed centrophilin, this protein associates with the minus‐ends of spindle microtubules (MT) and appears to be important in spindle organization [Tousson et al., 1991:J. Cell Biol.112:427–440]. Comparison of a partial cDNA sequence obtained for centrophilin with the full length cDNA sequence of nuclear mitotic apparatus protein (NuMA) [Compton et al., 1992:J. Cell Biol.116:1395–1408; Yang et al., 1992:J. Cell Biol.116:1303–1317] has indicated that NuMA and centrophilin are the same protein. Using a polyclonal NuMA antibody, we have provided further evidence that NuMA exists as iso‐forms as shown by peptide mapping and immunoblots. Sequential fractionation experiments along with immunofluorescence, immunoblotting, and EM immunogold labeling have demonstrated that NuMA isoforms are novel components of nuclear core filaments. Thus, NuMA, a long coiled‐coil protein, appears to have dual functions in interphase and mitosis during the cell cycle. In interphase, NuMA likely plays a structural role in the nucleoskeleton that may be important in nuclear organization and functions, whereas in mitosis, NuMA appears to be associated with spindle MT organization and chromosome positioning. © 1994 W

ISSN:0886-1544    

DOI:10.1002/cm.970290208

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

年代:1994

数据来源: WILEY

摘要:

AbstractFlagellar axonemes of sea urchin sperm display high frequency (200–400 Hz) vibration with nanometer scale amplitudes in the presence of ATP [Kamimura and Kamiya, 1992:J. Cell Biol.116:1443–1454]. To investigate how various axonemal components affect the vibration, we examined vibration in wild‐type and mutant axonemes ofChlamydomonas. At 1 mM ATP, wild‐type axonemes underwent vibration at 100–650 Hz with amplitudes of 4–40 nm. This vibration was similar to, but less regular than, that in sea urchin sperm. Axonemes of the mutantsida1 andida4 lacking part of the inner arm dynein underwent vibrations indistinguishable from that of wild‐type. The mutantoda1 lacking the entire outer arm underwent vibration at about half the wild‐type frequency. Unexpectedly, the paralyzed mutantspf18 lacking the central pair andpf14 lacking the radial spokes displayed vibration with significantly higher frequencies and smaller amplitudes than those in the wild‐type vibration. These results indicate that the high‐frequency vibration is common to many kinds of mutant axonemes that lack various axonemal substructures, but that its manner is sensitive to the presence of outer arm dynein and the central pair/radial spoke system. Simultaneous measurements of amplitude and frequency in wild‐type and mutant axonemes suggest that the velocity of microtubule sliding in vibrating axonemes is lower than the velocity of sliding under load‐free conditions. The velocity is particularly low inpf18. A possible mechanism is proposed to explain the lower sliding velocity and vibration amplitude in thepf18 axoneme, based on an assumption that central pair/radial spoke system may work to regulate the switching of two antagonizing forces within the axoneme.

ISSN:0886-1544    

DOI:10.1002/cm.970290209

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

年代:1994

数据来源: WILEY

摘要:

AbstractMotile spermatozoa of the polychaeteArenicola marinawere observed to swim intermittently. On the basis of the behaviour of the flagellum, the quiescent periods can be classified into two main types. The first are those in which, although the generation of the flagellar wave appears to be initiated, its passage down the axoneme appears blocked. This results in the formation of an acute bend (of approximately 2.65 rad) in the proximal region of the flagellum with the remainder of the axoneme remaining straight. These have been termed Type I quiescent periods and are very similar to the “cane‐shaped” configuration which has been described in the spermatozoa of some sea urchins. Sperm may also enter a Type II quiescent period, in which both the propagation and the generation of flagellar waves appears blocked. The flagellum of such sperm appears straight or slightly curved and they can remain in this configuration for several minutes. With increased intensity and duration of irradiation, the length of time spent in Type II quiescent period was increased significantly. Both types of quiescent period were (1) reduced in duration and frequency by deletion of calcium from artificial sea water (ASW); (2) either abolished or reduced in duration by the addition of 1 mM cadmium chloride to ASW. In addition, flagellar waveforms very similar to those displayed by spermatozoa in Type I quiescent periods could be induced (if only for a short time) by the addition of the divalent cation ionophore A23187 to ASW. It is suggested that this type of behaviour may be induced following an influx of calcium into the intraflagellar compartment of spermatozoa and that this may be mediated by certain intensities and wavelengths of light. © 1994 Wiley‐L

ISSN:0886-1544    

DOI:10.1002/cm.970290210

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

年代:1994

数据来源: WILEY

ISSN:0886-1544    

DOI:10.1002/cm.970290201

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

年代:1994

数据来源: WILEY