bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetochore microtubules shorten by loss of subunits at the kinetochores of prometaphase chromosomes
Authors: Cassimeris Lynne , Salmon E. D. 
Published: April 2021

ABSTRACT
The site of tubulin subunit dissociation was determined during poleward chromosome movement in prometaphase newt lung cell mitotic spindles using fluorescence photobleaching techniques and nocodazole-induced spindle shortening. Synchronous shortening of all kinetochore microtubules was produced by incubating cells in 17 μM nocodazole to block microtubule assembly. Under these conditions the spindle poles moved towards the metaphase plate at a rate of 3.6±0.4 μmmin−1 (n=3). On the basis of anti-tubulin immunofluourescent staining of cells fixed after incubation in nocodazole, we found that nonkinetochore microtubules rapidly disappeared and only kinetochore fibers were present after 60–9 0 s in nocodazole.
To localize the site of tubulin subunit dissociation, a narrow bar pattern was photobleached across one half-spindle in prometaphase-metaphase cells previously microinjected with 5-(4,6-dichlorotriazin-2-yl) amino fluorescein (DTAF)-labeled tubulin. Immediately after photobleaching, cells were perfused with 17 μM nocodazole to produce shortening of kinetochore microtubules. Shortening was accompanied by a decrease in the distance between the bleach bar and the kinetochores. In contrast, there was little or no decrease in the distance between the bleach bar and the pole. Compared to their initial lengths, the average kinetochore to pole distance shortened by 18 %, the bleach bar to kinetochore distance shortened by 28% and the average bleached bar to pole distance shortened by 1.6%. The data provide evidence that tubulin subunits dissociate from kinetochore microtubules at a site near the kinetochore during poleward chromosome movement These results are consistent with models of poleward force generation for chromosome movement in which prometaphase-metaphase poleward force is generated in association with the kinetochore.
Neomycin reversibly disrupts mitotic progression in stamen hair cells of Tradescantia
Authors: Larsen Paul M. , Chen Tung-Ling L. , Wolniak Stephen M. 
Published: April 2021

ABSTRACT
Neomycin has been reported to inhibit polyphosphoinositide cycling by preventing the hydrolysis of phosphatidylinositol 4,5-bisphosphate into inositol 1,4,5-trisphosphate and 1,2-diacylglycerol. Inositol 1,4,5-trisphosphate, through the mobilization of calcium, and 1,2-diacylglycerol, through the activation of protein kinase C, trigger many physiological responses. The addition of 2 mM neomycin to stamen hair cells of Tradescantia virginiana at various [mints during mitosis arrests cells in prophase, prior to nuclear envelope breakdown, or in metaphase. Arrest in prophase is irreversible. Metaphase arrest can persist for over 2h before the cells attempt to revert to interphase without dividing. Entry into anaphase by the majority of cells in our sample arrested in metaphse occurred after treatment with 1,2-dioctanoylglycerol while 1,3-dioctanoylglycerol was totally ineffective at reversal. Perfusion of 100 μM calcium chloride solution past the cells was sufficient to reverse arrest in approximately half of the cells in the sample. Magnesium could not be substituted for calcium in the reversal. Clindamycin, another member of this class of aminoglycoside antibiotics, with no known inhibitory effect on polyphosphoinositide cycling, is without effect on mitotic progression in stamen hair cells. Our results indirectly implicate one or more episodes of polyphosphoinositide cycling and its resultant protein phosphorylation by protein kinase C in the regulatory cascade that leads to anaphase.
Polarity in spontaneous unwinding after prior rotation of the flagellar beat plane in sea-urchin spermatozoa
Authors: Takahashi Keiichi , Shingyoji Chikako , Katada Jun , Eshel Dan , Gibbons I. R. 
Published: April 2021

ABSTRACT
The flagellar beat plane of live and reactivated seaurchin sperm held by their heads in the tip of a vibrating micropipette will rotate along with the plane of the imposed vibration for up to 10 revolutions in either a clockwise or a counterclockwise direction. Subsequent cessation of the imposed vibration is followed by spontaneous unwinding of the flagellar beat plane. Nearly complete unwinding occurs after prior counterclockwise winding. The unwinding of the beat plane after prior clockwise winding is incomplete, but the number of revolutions that remain unwound affects the response of the flagellar beat plane to a second set of imposed revolutions. The initial angular velocity of spontaneous unwinding is approximately proportional to the number of prior winding cycles, independent oftheir direction. The maximum initial velocity of unwinding was 27rad s−1 and 20rad s−1 for live and reactivated sperm, respectively. These data suggest that the force responsible for unwinding of the beat plane is derived from the elastic distortion of some component in the axonemal structure. The difference in completeness of spontaneous unwinding between the two directions of rotation is consistent with the previously suggested hypothesis that imposed rotation of the beat plane reflects the forced rotation of the central pair within the axoneme.
Abnormal chromatin (abc), a maternal-effect locus in Drosophila melanogaster
Authors: Vessey Kristin B. , Ludwiczak Rachael L. , Briot Amy S. , Underwood Eileen M. 
Published: April 2021

ABSTRACT
Mutations in the maternal-effect gene abnormal chromatin (abc) in Drosophila melanogaster result in a variety of defects involving nuclear replication/ division. Three recessive alleles of this gene, which maps near 51F on chromosome 2, all result in female sterility. They cause slower embryonic development that is usually abnormal from the earliest nuclear divisions and arrested by the sixth one. Nuclei tend to be large and erratically distributed, some intensely staining. Mitotic asynchrony is common. Few embryos reach the gastrula stage and none hatch. With the weakest allele, fsPL, bridges between nuclei are common; abnormal chromatin clumps that resemble yolk nuclei occur before the other nuclei reach the surface; and spindle anomalies and DNA wads with numerous centrosomes are seen. Females with the stronger alleles, fsA5 and fs27, lay fewer eggs and a smaller proportion of embryos reach blastoderm; developmental arrest occurs earlier, usually with several large nuclei distributed along the length of the embryo. Chorion defects occur in all three mutants. Mitotic asynchrony, nuclear bridging, endoreduplication and nuclear behavior aberrant from the first division suggest that the abc gene product operates in DNA replication/nuclear division. Larval (homozygous F1) neuroblast chromosome structure and mitotic indices are normal, indicating that any mitotic function is strictly maternal, i.e. abc is not a general mitotic gene. Thus abc is one of a few known genes with a maternal effect that appears to function in the embryonic cell cycle.
Implications of DNA replication for eukaryotic gene expression
Authors: Wolffe Alan P. 
Published: April 2021

ABSTRACT
DNA replication has a key role in many developmental processes. Recent progress in understanding events at the replication fork suggests mechanisms for both establishing and maintaining programs of eukaryotic gene activity. In this review, I discuss the consequences of replication fork passage for pre existing chromatin structures and describe how the mechanism of nucleosome assembly at the replication fork may facilitate the formation of either transcriptionally active or repressed chromatin.
Cytoskeletal targets for oncogenic tyrosine kinases
Authors: Kellie S. , Horvath A. R. , Elmore M. A. 
Published: April 2021

ABSTRACT
The past decade has seen intense investigation into the role of tyrosine phosphorylation in cell growth and tumorigenesis (Cooper and Hunter, 1983). Whilst it is now well established that receptor occupancy by a number of growth factors is associated with tyrosine phosphorylation, the signal transduction pathways and the mechanism by which oncogenic tyrosine kinases induce cell growth and neoplastic changes remain elusive (Jove and Hanafusa, 1987; Yarden and Ullrich, 1988). The acutely transforming avian sarcoma viruses have been invaluable tools for examining the molecular basis underlying the changes in cell morphology and growth regulation that occur during neoplasia. The src gene product of Rous sarcoma virus (RSV) is probably the best-characterised oncogenic tyrosine kinase, and we shall review the evidence showing that components of the cytoskeleton are functional targets for this enzyme.
Assembly of a chondrocyte-like pericellular matrix on non-chondrogenic cells Role of the cell surface hyaluronan receptors in the assembly of a pericellular matrix
Authors: Knudson Warren , Knudson Cheryl B. 
Published: April 2021

ABSTRACT
In this study, we have examined the capacity of various cell types, which express cell surface hyaluronan receptors, to organize a chondrocyte-like pericellular matrix when given chondrocyte-derived extracellular matrix macromolecules exogenously. The assembly of a pericellular matrix was visualized by a particle exclusion assay. Without the addition of exogenous macromolecular components, none of the cell types studied exhibited significant pericellular matrices extending from their plasma membranes. However, upon the addition of high molecular weight hyaluronan in combination with aggregating cartilage proteoglycan monomers, large pericellular matrices were formed within two hours of incubation. No pericellular matrices were formed if these macromolecular components were added separately at equivalent concentrations or if the components were added in the presence of hyaluronan hexasaccharide, a competitive inhibitor of hyaluronan interaction with cell surface hyaluronan receptors. Fully assembled pericellular matrices could also be displaced by the subsequent addition of hyaluronan hexasaccharides. Nonliving, glutaraldehyde-fixed cells, which retained functional hyaluronan receptors, maintained the capacity to assembly pericellular matrices with exogenous components, in serumcontaining or serum-free medium. Cells that were incubated with exogenous matrix macromolecules for 24 h, followed by a chase incubation in medium minus the exogenous macromolecules, continued to maintain the matrix for up to 6 h on live cells and more than 24 h on glutaraldehyde-fixed cells. Cell types that did not express hyaluronan receptors were not capable of organizing such pericellular matrices when incubated with these exogenous components. These findings suggest that cells expressing hyaluronan receptors have a significant capacity to organize their immediate extracellular environment via hyaluronan-hyaluronan receptor interactions. Possible physiological functions for this type of matrix organizing capacity are discussed.
Effects of β-xylosides on proteoglycan biosynthesis and morphology of PC12 pheochromocytoma cells and primary cultures of rat cerebellum
Authors: Margolis R. K. , Goossen B. , Tekotte H. , Hilgenberg L. , Margolis R. U. 
Published: April 2021

ABSTRACT
We have examined the effects of β-xylosides, which act as exogenous acceptors for glycosaminoglycan chain initiation, on the morphology and proteoglycan biosynthesis of PC 12 pheochromocytoma cells, and on monolayer, aggregate and explant cultures of early postnatal rat cerebellum. PC 12 cells cultured for 13 days in the presence of nerve growth factor (NGF) and β-xyloside, and labeled during days 11-13 with sodium [35S]sulfate, showed an 8- to 11-fold increase in [35S]sulfate-labeled macromolecules released into the culture medium. Most of the increase was accounted for by chondroitin sulfate, which was in the form of free glycosaminoglycan chains, which were not acid-precipitable. The presence of β-xylo-side also led to a 65-115% increase in [35S]sulfate incorporation into cell-associated glycosaminoglycans and glycoproteins of untreated and NGF-treated PC 12 cells, respectively. β-Xyloside treatment reduced the size of the chondroitin sulfate chains in both the cells and medium from approximately 34 000 to 10000Mr, but had much less effect on heparan sulfate, which decreased in size from 16000 to 13 000-14 500 Mr (in the medium and cells, respectively). β-Xyloside inhibition of proteoglycan biosynthesis was accompanied by significant morphological effects in NGF-treated PC12 cells, consisting of an increase in length and decrease in the branching, diameter and adhesion to the collagen substratum of the PC 12 cell processes. p-Nitrophenyl- and 4-methylumbelliferyl-β-D-xylosides produced similar effects, which were not seen with p-nitrophenyl-β-D-galactoside. fi-Xylosides also produced distinct alterations in the adhesion and morphology of monolayer, aggregate, and explant cultures of early postnatal rat cerebellum, which occurred together with inhibition of chondroitin sulfate proteoglycan biosynthesis and a decrease in glycosaminoglycan chain size. These studies indicate that chondroitin sulfate (and probably also heparan sulfate) proteoglycans play a significant role in modulating cell-cell and cellmatrix interactions in nervous tissue development and differentiation.
Cytoskeletal rearrangements accompanying Salmonella entry into epithelial cells
Authors: Finlay B. Brett , Ruschkowski Sharon , Dedhar Shoukat 
Published: April 2021

ABSTRACT
Salmonella bacteria can enter (invade) eukaryotic cells, and exist as intracellular parasites. Confocal, light immunofluoresence and electron microscopy were used to examine various cytoskeletal components of cultured Madin Darby canine kidney (MDCK) and HeLa epithelial cells after infection with Salmonella typhimurium. These bacteria entered and remained within membrane-bound vacuoles and were surrounded by large (5-10 μm) dense structures composed of various cytoskeletal components. These structures consisted of extensive aggregations of polymerized actin, a-actinin and tropomyosin above and beside the invading bacterium in both epithelial cell lines. These structures were evident soon after bacterial addition (maximal at 20 min for HeLa cells, 60 min for MDCK cells), and disappeared later in the infection as the cytoskeletal components returned to a more normal distribution after bacterial internalization. Surprizingly, tubulin also aggregated above internalized Salmonella although bacterial entry or penetration through polarized monolayers was not disrupted by the microtubule-inhibiting agent nocadazole (this treatment actually enhanced tubulin accumulation around these organisms). There were little if any rearrangements in intermediate filaments composed of keratin or vimentin. Large amounts of talin also accumulated above and around invading Salmonella, but there was only a minor accumulation of vinculin around a few organisms. Pretreatment of epithelial cells with the microfilament inhibitor cytochalasin D blocked bacterial internalization but did not prevent accumulation of polymerized actin and a-actinin directly beneath uninternalized bacteria, yet prevented accumulation of the other cytoskeletal components. These results suggest that Salmonella bind to the surface and trigger a signal in epithelial cells that causes marked rearrangements in various cytoskeletal components, including recruitment of actin filaments and a-actinin, which then generates the force necessary for bacterial uptake.
Chemoreceptor-mediated elongation of stereocilium bundles tunes vibration-sensitive mechanoreceptors on cnidocyte-supporting cell complexes to lower frequencies
Authors: Watson Glen M. , Hessinger David A. 
Published: April 2021

ABSTRACT
Cnidocyte-supporting cell complexes (CSCCs) discharge nematocysts into targets upon coincidental stimulation of specific chemoreceptors and contactsensitive mechanoreceptors. In addition, CSCCs in the tentacles of at least one species of sea anemone discharge nematocysts into targets vibrating at specific frequencies. In seawater alone, these CSCCs discharge nematocysts preferentially at 55, 50 and 75 Hz. In the presence of 10−7M N-acetylneuraminic acid (NANA) or mucin, the CSCCs discharge nematocysts preferentially at the lower frequencies of 0, 5, 15, 30 and 40 Hz. Furthermore, the stereocilium bundles (SBs) within ciliary cones of CSCCs elongate significantly from a mean length of 6.08 /on in seawater to 7.14 μm in 10−7M mucin. The responses of (1) shifting the optimal frequencies for discharging nematocysts to lower frequencies and (2) elongating the SBs both exhibit dose-dependency and temporal adaptation to chemosensitizer. We conclude that these responses are controlled by CSCC chemoreceptors for N-acetylated sugars. We suggest that specific size-classes of SBs respond to specific frequencies of vibration, since the dose-response parameters to NANA depicting the relative abundances of SB size classes measuring 3–4, 5 and 7 μm correlate with dose-response parameters for the discharge of nematocysts into targets vibrating at 75, 55, and 30 Hz. Treating tentacles with cytochalasin disorganizes the SBs of ciliary cones and decreases the number of frequency optima for nematocyst discharge without significantly affecting nematocyst discharge into static targets. Thus, ciliary cones on CSCCs are vibration-sensitive mechanoreceptors that can be tuned by chemoreceptors to specific, lower frequencies by the elongation of SBs.
Effects of truncated neurofilament proteins on the endogenous intermediate filaments in transfected fibroblasts
Authors: Chin Steven S. M. , Macioce Pompeo , Liem Ronald K. H. 
Published: April 2021

ABSTRACT
The expression and assembly characteristics of carboxyl- and amino-terminal deletion mutants of rat neurofilament low Mr (NF-L) and neurofilament middle Mr (NF-M) proteins were examined by transient transfection of cultured fibroblasts. Deletion of the carboxyl-terminal tail domain of either protein indicated that this region was not absolutely essential for co-assembly into the endogenous vimentin cytoskeleton. However, deletion into the α-helical rod domain resulted in an inability of the mutant proteins to co-assemble with vimentin into filamentous structures. Instead, the mutant proteins appeared to be assembled into unusual tubular-vesicular structures. Additionally, these latter deletions appeared to act as dominant negative mutants which induced the collapse of the endogenous vimentin cytoskeleton as well as the constitutively expressed NF-H and NF-M cytoskeletons in stably transfected cell lines. Thus, an intact a-helical rod domain was essential for normal IF co-assembly whereas carboxyl-terminal deletions into this region resulted in dramatic alterations of the existing type HI and IV intermediate filament cytoskeletons in vivo. Deletions from the amino-terminal end into the a-helical rod region gave different results. With these deletions, the transfected protein was not co-assembled into filaments and the endogenous vimentin IF network was not disrupted, indicating that these deletion mutants are recessive. The dominant negative mutants may provide a novel approach to studying intermediate filament function within living cells.
Expression in escherichia coli of human lamins A and C: influence of head and tail domains on assembly properties and paracrystal formation
Authors: Moir Robert D. , Donaldson Anne D. , Stewart Murray 
Published: April 2021

ABSTRACT
We have expressed in Escherichia coli cDNA corresponding to human lamins A and C, together with a number of fragments produced using site-specific mutagenesis. The proteins produced in this way were characterised both biochemically and ultrastructurally, and appeared to retain their native conformation. Crosslinking showed that all fragments formed 4-chain molecular dimers (‘tetramers’) analogous to those formed by intact intermediate filament proteins. Shadowed preparations showed the presence of rod-like particles that closely resembled those observed for other intermediate filament proteins and their proteolytically prepared rod domains. Moreover, the expressed lamins and a series of fragments in which different domains had been deleted formed paracrystals similar to those observed with native material. Deletion of either the Nor C-terminal non-helical domains altered the solubility and aggregation properties of the expressed protein, indicating that both domains have a role in lamin assembly.
Cell density affects spreading and clustering, but not attachment, of human keratinocytes in serum-free medium
Authors: Malcovati Massimo , Tenchini Maria Luisa 
Published: April 2021

ABSTRACT
Attachment, spreading and clustering of second-passage human keratinocytes in serum-free medium have been evaluated within 24 h after plating, as a function of the density of the inoculum and of time, in two different strains.
The results show that attachment is unaffected by cell density and differs significantly from strain to strain.
Cell density affects the distribution of attached keratinocytes among three morphologically distinct classes: unspread, spread and clustered cells. The percentage of unspread keratinocytes shows a linear decrease at increasing cell density, and that of spread keratinocytes an increase, resulting from statistically significant increases in the percentages of both single and clustered cells. Spreading on uncoated surfaces appears therefore as an inducible phenomenon. The use of media conditioned by keratinocytes, fibroblasts and HeLa cells shows that keratinocytes specifically secrete a diffusible ‘spreading factor’. We term this phenomenon ‘autocrine induced spreading’. Preliminary physicochemical characterization suggests that a protein could be responsible for the spreading activity of conditioned media. The ‘spreading factor’ seems to act directly on the cells, and not through a modification of the plastic surface of the dishes, since most (&gt;70%) of the spreading activity can be recovered in the conditioned media used in pre-coating experiments.
The percentages of clusters follow ‘saturation’ kinetics at increasing cell density, while the percentage of clustered cells increases linearly with the density of inoculum.
Time-course experiments show that the rate of spreading is cell density- and strain-independent. The percentages of clusters and of total clustered cells are time-independent, suggesting that cluster formation takes place in suspension.
These data indicate the existence of a complex functional heterogeneity of cultured human keratinocytes.