ISSN:0886-1544    

DOI:10.1002/cm.970200102

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn a previous study (J. Cell Biol.109:1229–1243, 1989), we reported that conditions which increased growth cone calcium levels and induced neurite retraction in cultured chick DRG neurons also resulted in an apparent loss of actin filaments in the growth cone periphery. We further showed that the actin‐stabilizing drug phalloidin could block or reverse calcium‐ionophore‐induced neurite retraction, indicating that the behavioral changes were mediated, at least in part, by changes in actin filament stability. In this study, we have further characterized the calcium sensitivity of growth cone behavior to identify which features of calcium‐induced behavioral effects can be attributed to effects on actin filaments alone, and to assess whether two other second‐messenger systems, cAMP and protein kinase C, might influence neurite outgrowth by altering calcium levels or actin stability. The results indicated that growth cone behavior was highly sensitive to small changes in calcium concentrations. Neurite outgrowth was only observed in calcium‐permeabilized cells when extracellular calcium concentrations were between 200 and 300 nM, and changes as small as 50 nM commonly produced detectable changes in behavior. Furthermore, low doses of cytochalasins mimicked all of the grossly observable features of growth cone responses to elevation of intracellular calcium, including the apparent preferential destruction of lamellipodial actin filaments and sparing of filopodial actin, suggesting that the behavioral effects of calcium elevation could be explained by loss of actin filaments alone. The effects of cAMP elevation and protein kinase C activation on growth cone behavior, ultrastructure, and fura2‐AM‐measured calcium levels indicated that the effects of cAMPmanipulations could be partially explained by a cAMP‐induced lowering of growth cone calcium levels and concomitant increased stabilization of actin filaments, but protein kinase C appeared to act through an in

ISSN:0886-1544    

DOI:10.1002/cm.970200103

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe tyrosinylation of chick brain α‐tubulin and the effects of the tyrosinylation status on the assembly and dynamic instability of chick brain MAP2:tubulin microtubule protein have been examined. Each of the eight major α‐isotypes can be tyrosinylated in vitro, irrespective of whether a C‐terminal tyrosine is genetically encoded. The extent of tyrosinylation is however limited to ≏ 0.3 mol.mol−1. The tyrosinylation status (0 vs. 0.3 mol.mol−1) has no effect on either the assembly kinetics of chick brain microtubule protein or on the rate of length redistribution following assembly and shearing. It is therefore unlikely that the tyrosinylation status directly affects the intrinsic stability of assembled microtu‐bules since the rate of length redistribution is both a sensitive assay and a function of the kinetic parameters governing dyna

ISSN:0886-1544    

DOI:10.1002/cm.970200104

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

年代:1991

数据来源: WILEY

摘要:

AbstractCiliated sheets of cell cortex were prepared from Triton‐glycerol‐extractedParameciumto observe directly the change of ciliary orientation. The observation of the ciliary responses revealed the modes of ciliary control by Ca2+and cyclic nucleotides. The cilia changed their pointing direction clockwise from 11–12 to 5 o'clock (with the anterior of the cell defined as 12 o'clock) in the horizontal plane of cell surface when Ca2+concentration was decreased from 10−6M to 10−7M. Cyclic AMP competed with Ca2+ion in determining the orientation of the cilia. On the other hand, cGMP tended to change the ciliary orientation toward 3 o'clock. Ciliary sensitivity to cyclic nucleotides depended on their location on the cell surface. The cilia on the left‐hand field of the cell were more sensitive to cyclic nucleotide than those on the right‐hand field. The differential distribution of ciliary sensitivity within a single cell seems to be functional in the sophisticated turning mechanism in the behavioral response

ISSN:0886-1544    

DOI:10.1002/cm.970200105

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe segregation of the nucleolus during mitosis was examined inSaccharomyces cerevisiaeandSchizosaccharomyces pombeby indirect immunofluorescence using antibodies directed to highly conserved anti‐nucleolus antigens. In mitotic S.pombecells, the nucleolus appears to trail the bulk of the DNA. In wild‐type cells of S.cerevisiae, the nucleolus segregates alongside the bulk of the genomic DNA. Based on its distance from the centromere, we would expect the rDNA in both organisms to segregate behind the majority of the genomic DNA, if telomeric regions trail centromeric regions as in other eukaryotes. We therefore suggest that inS. cerevisiaethe nucleolus is attached to other parts of the nucleus which enable it to segregate along with the bulk of the DNA. The segregation of the nucleolus in topoisomerase mutants and nuclear division mutants of S.cerevisiaewas also investigated. Incdc14mutants which arrest at late anaphase, the vast majority of the DNA is separated, but the nucleolar antigens remain extended between the mother and daughter cells. Thus, theCDC14gene ofS. cerevisiaeappears to be important for the separation of the nucleolus at mito

ISSN:0886-1544    

DOI:10.1002/cm.970200106

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe movement of live trout spermatozoa is very brief (25 sec at 20°C) and conditions have been developed to get synchronous initiation of sperm motility which allowed quantification of the major parameters of sperm movement during the motility phase.Recorded flagellar beat frequencies decreased steadily from values of 55 Hz at the beginning to 20 Hz at the end of the motility phase. Sperm forward velocities followed a similar pattern from 250 to 20 μm.sec−1in the same conditions and the diameters of sperm trajectories were reduced from 370 to 40 μm. Thus none of the characteristics of sperm movement was constant during the motile phase which ended abruptly by a straightening of the flagella.The decrease in flagellar beat frequencies and sperm velocities are much greater than what could be extrapolated from the decrease of intracellular ATP (Christen R. et al: Eur. J. Biochem, 166:667–671, 1987) or from measurements of ATP‐dependence of reactivated sperm velocities (Okuno M. and Morisawa N.: In Biological Functions of Microtubules and Related Structures. New York: Academic Press, pp. 151–162, 1982). Therefore, the cessation of flagellar beating at 25 sec is not directly the result of the low concentration of intracellular ATP.The decrease in the diameters of sperm trajectories which occurred during the first part of the motility phase was correlated with [Ca]imeasurements (Cosson M.P. et al, Cell Motil. Cytoskeleton, 14:424–434, 1989). The effect of Ca2+at the axonemal level does not indicates that Ca2+influx is previous to flagellar beating but rather suggests a classical Ca2+regulation of the flagellar assymetry.The short duration of the motility phase and the characteristics of sperm movement were very similar in various conditions (high external K+, low pH media) where increased external Ca2+or divalent ions were shown to overcome K+and H+inhibition of sperm motility, both conditions which have been shown to depolarize the plasma membrane potential (Gatti J.L. et al: J. Cell Physiol., 143:546–554, 1990).The present study of the parameters of sperm movement suggests that once motility is initiated, a defined set of axonemal events will take place whatever the exter

ISSN:0886-1544    

DOI:10.1002/cm.970200107

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe dense‐bodies in the body wall muscle of the nematodeCaenorhabditis elegansfunction to anchor the actin thin filaments to the adjacent sarcolemma. One of the major components of the dense‐bodies is the actin‐binding protein α‐actinin. To facilitate a genetic analysis of α‐actinin, we have cloned a cDNA encoding the nematode protein, identified its position on the nematode physical map, and developed a unique PCR based approach to test the position of the cloned gene relative to known genetic deletions. The peptide sequence deduced from the cDNA shows that, apart from a few exceptional regions, the nematode protein shows strong similarity to other known α‐actinins. Its position on the genetic map shows that none of the known muscle affecting mutations identified inC. elegansare in this α‐actinin gene. This gene has been given the namea

ISSN:0886-1544    

DOI:10.1002/cm.970200108

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

年代:1991

数据来源: WILEY

ISSN:0886-1544    

DOI:10.1002/cm.970200101

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

年代:1991

数据来源: WILEY