bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interference in vimentin assembly in vitro by synthetic peptides derived from the vimentin head domain
Authors: Hofmann Ilse , Herrmann Harald 
Published: April 2021

ABSTRACT
The importance of the amino-terminal domain (“head”) of type HI intermediate filament (IF) proteins in IF assembly has been examined by testing the influence of synthetic peptides representing a highly conserved decameric motif, , located near the amino terminus of vimentin. When added to soluble vimentin subunits this peptide induces, at fourfold molar excess or slightly above, the appearance of short, regular rod-like structures as determined by electron microscopy of negatively stained and rotary-shadowed preparations as well as by viscometry. At higher peptide concentrations large, irregularly shaped aggregates of mostly non-IF structures formed, but this aggregation was reversible by prolonged dialysis against low ionic strength buffer. The aggregating effect of this peptide was highly sequence-specific and was not seen with point-mutated sequences such as RR → TR or with unrelated peptides containing a central diarginine, indicating that it is not simply ionic. When different hexapeptides representing different “head” positions were compared, only the central sequence, SYRRXF, was as effective as the decamer.
The addition of peptide during IF assembly did not prevent filament formation, although 50-fold molar excess of peptide resulted in a drastic increase (up to 40 nm) in the width of the filaments, which also appeared less regular, thus reflecting some interference with assembly. In contrast to the effects on soluble vimentin, the decameric peptide did not disturb Ils, indicating that the binding domain is “masked” or stabilized in the filaments.
To identify the domain to which the peptide binds, three different binding assays using vimentin fragments and genetically engineered vimentin deletion mutants were employed. The results indicate that the binding domain of the near-amino-terminal peptide is located at the start of the α-helical “rod” domain of the protein. Possible mechanisms of interaction of these two portions of vimentin during IF assembly are discussed.
WASP and WAVE family proteins: key molecules for rapid rearrangement of cortical actin filaments and cell mov
Authors: Takenawa Tadaomi , Miki Hiroaki 
Published: April 2021

ABSTRACT
Reorganization of cortical actin filaments plays critical roles in cell movement and pattern formation. Recently, the WASP and WAVE family proteins WASP and N-WASP, and WAVE1, WAVE2 and WAVE3 have been shown to regulate cortical actin filament reorganization in response to extracellular stimuli. These proteins each have a verprolin-homology (V) domain, cofilin-homology (C) domain and an acidic (A) region at the C-terminus, through which they activate the Arp2/3 complex, leading to rapid actin polymerization. N-WASP is usually present as an inactive form in which the VCA region is masked. Cooperative binding of Cdc42 and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) exposes the VCA region, activating N-WASP. In addition to this activation mechanism, WISH also activates N-WASP independently of Cdc42 and PtdIns(4,5)P2, by binding to the proline-rich region of N-WASP. N-WASP activation induces formation of filopodia in vivo. In contrast, the ubiquitously expressed form of WAVE2 is activated downstream of Rac, leading to formation of lamellipodia. In this case, IRSp53 transmits a signal from Rac to WAVE2 through formation of a ternary Rac-IRSp53-WAVE2 complex. Thus, N-WASP, which is activated downstream of Cdc42 or independently by WISH, induces formation of filopodia and WAVE2, which is activated via IRSp53 downstream of Rac, induces formation of lamellipodia.
Wild-type, mitochondrial and ER-restricted Bcl-2 inhibit DNA damage-induced apoptosis but do not affect death receptor-induced apoptosis
Authors: Rudner Justine , Lepple-Wienhues Albrecht , Budach Wilfried , Berschauer Johannes , Friedrich Björn , Wesselborg Sebastian , Schulze-Osthoff Klaus , Belka Claus 
Published: April 2021

The proto-oncogene Bcl-2 is expressed in membranes of mitochondria and endoplasmic reticulum and mediates resistance against a broad range of apoptotic stimuli. Although several mechanisms of Bcl-2 action have been proposed, its role in different cellular organelles remains elusive. Here, we analyzed the function of Bcl-2 targeted specifically to certain subcellular compartments in Jurkat cells. Bcl-2 expression was restricted to the outer mitochondrial membrane by replacing its membrane anchor with the mitochondrial insertion sequence of ActA (Bcl-2/MT) or the ER-specific sequence of cytochrome b5 (Bcl-2/ER). Additionally, cells expressing wild-type Bcl-2 (Bcl-2/WT) or a transmembrane domain-lacking mutant (Bcl-2/ΔTM) were employed. Apoptosis induced by ionizing radiation or by the death receptors for CD95L or TRAIL was analyzed by determination of the mitochondrial membrane potential (ΔΨm) and activation of different caspases.
Bcl-2/WT and Bcl-2/MT strongly inhibited radiation-induced apoptosis and caspase activation, whereas Bcl-2/ΔTM had completely lost its anti-apoptotic effect. Interestingly, Bcl-2/ER conferred protection against radiation-induced mitochondrial damage and apoptosis similarly to Bcl-2/MT. The finding that ER-targeted Bcl-2 interfered with mitochondrial ΔΨm breakdown and caspase-9 activation indicates the presence of a crosstalk between both organelles in radiation-induced apoptosis. By contrast, Bcl-2 in either subcellular position did not influence CD95- or TRAIL-mediated apoptosis.
Fine structure of the ventral disk apparatus and the mechanism of attachment in the flagellate Giardia muris
Authors: Holberton D. V. 
Published: April 2021

ABSTRACT
The topography of the Giardia trophozoite is dominated by the large domed sucking disk of the ventral surface. Attached to the host duodenal epithelium, the rim of this disk penetrates the enteric surface coat and interdigitates with microvilli of the epithelial cells, approaching to within 20 nm of the host surface membrane. Distortion of the host brush border within the disk suggests an applied suction force. A mechanical explanation of disk action is sought in a detailed description of the fine structure of components of the ventral surface - but is found to be untenable. The disk is supported by a platform of modified 25-nm microtubules, linked to the ventral membrane by side arms and bearing heavily cross-linked vertical dense ribbons. It is argued that such is the architecture of rigidity rather than relative movement.
Around the disk a mobile cytoplasmic flange is supported by 2 lateral plates of periodic substructure. The flange has no clear mechanical role in attachment; a likely evolutionary origin from a component of the anterior axonemal axis is suggested.
The cavity of the ventral disk leads posteriorly through a portal into the ventrocaudal groove: a shallow depression that houses the ventral flagella. Observation of isolated living trophozoites suggests that attachment depends on the continuing activity of the ventral flagella, which normally beat synchronously in a sinusoidal waveform. Electron micrographs confirm that this waveform is maintained in situ on the host epithelium. Of the 4 pairs of flagella, the ultrastructure of the ventral flagella is notable for additional components in the flagellar shaft, including an intraflagellar dense rod linked to 3 axonemal doublets by fine connectives.
From a consideration of analogous macroscopic systems, a preliminary hydrodynamic analysis is advanced in which the suction force of attachment follows from the pattern of fluid flow induced by the beating ventral flagella.
The significance of the conclusion that cytoplasmic microtubules (or structures derived from them) apparently maintain cell shape in the face of an applied external force is discussed.
Observations on the origin and significance of the nuclear envelopelimited monolayers of chromatin unit threads associated with the cell nucleus
Authors: Haynes M. E. , Davies H. G. 
Published: April 2021

ABSTRACTMonolayers of chromatin structural units about 33·0 nm in width enclosed on both sides by extensions of the nuclear envelope, called sheets, and located either in the cytoplasm (c· ·n· ·c type), or within the nucleus (c·· n ··n type), are common in cultured cells of Burkitt’s lymphoma. The sheets are absent from mitotic cells except at telophase where, unlike interphase, type c· ·n··n is more numerous than c· ·n··c. The degree of nuclear asymmetry is defined in terms of the increase in enclosing membranes over that required to enclose the same area in a circular configuration. The percentage number (Ps) of cells with nucleus-associated sheets averaged over all stages in the cell cycle, increases with cell viability and with nuclear asymmetry. However, during the cycle there is a marked diminution in Ps during the S-phase of DNA synthesis when nuclear asymmetry itself does not change. Hence, it is suggested, and data on other cell types support the hypothesis, that nuclear asymmetry is a necessary but not sufficient factor in causing sheets to form. Microtubules are present within the cytoplasm and their morphological arrangement suggests a role in determining nuclear asymmetry. Treatment with a microtubule depolymerizing agent, colcemid, does not alter either the existing nuclear asymmetry or Ps but when cells are treated early in S-phase the reappearance of sheets in the G2 phase of the cell cycle is considerably delayed. The reappearance takes place when the microtubules are still depolymerized. It is suggested that synthesis of membrane in excess of what is needed to enclose a sphere results in nuclear asymmetry and associated membrane-enclosed monolayers, the resulting nuclear conformation, including the distribution of membrane between types c··n· ·n and c··n··c, depending on what is energetically favoured. No biochemical function has yet been assigned to sheets.
Evidence for erythrocyte-specific histone modification and structural changes in chromatin during goose erythrocyte maturation
Authors: Brasch K. , Adams G. H. M. , Neelin J. M. 
Published: April 2021

ABSTRACT
Regenerating blood of geese suffering from phenylhydrazine anaemia was separated into ‘mature’ and ‘immature’ cell populations by centrifugation through a barrier of BSA. Socalled ‘mature cells’ consisted of mainly mature erythrocytes and ‘immature cells’ included two-thirds polychromatic and younger erythroblasts. Histone proteins, dissociated from isolated nuclei of both populations of cells by sequential extraction with citric acid and hydrochloric acid, were compared and the nuclei were examined by electron microscopy. Erythrocyte-specific histone V (f2c) was fully extracted from immature nuclei at pH 2·0, but only partially extracted at the same pH from mature nuclei. An inverse correlation was found between relative ease of extraction and alkali-labile phosphate content of purified samples of histone V. The more readily dissociated fraction of histone V from immature nuclei had a higher phosphate content than the less readily dissociated component V from immature and mature nuclei. Chromatin in mature nuclei became tightly congealed after only partial extraction of histone V at pH 2·0, but loosened visibly after subsequent full extraction of histone V at pH 1·8. In contrast, chromatin in immature nuclei never became totally congealed. Histone V may be a tissue-specific agent involved in packing of DNA within chromatin fibrils. During erythropoiesis, progressive decrease of histone V phosphate may lead to its increased binding affinity for chromatin and thus to the gradual transformation of the erythrocyte genome into a permanently repressed state.
Basal body and flagellar development during the vegetative cell cycle and the sexual cycle of Chlamydomonas reinhardii
Authors: Cavalier-Smith T. 
Published: April 2021

ABSTRACT
Basal body development and flagellar regression and growth in the unicellular green alga Chlamydomonas reinhardii were studied by light and electron microscopy during the vegetative cell cycle in synchronous cultures and during the sexual life cycle.
Flagella regress by gradual shortening prior to vegetative cell division and also a few hours after cell fusion in the sexual cycle. In vegetative cells basal bodies remain attached to the plasma membrane by their transitional fibres and do not act as centrioles at the spindle poles during division. In zygotes the basal bodies and associated microtubular roots and cross-striated connexions all dissolve, and by 6·5 h after mating all traces of flagellar apparatus and associated structures have disappeared. They remain absent for 6 days throughout zygospore maturation and then are reassembled during zygospore germination, after meiosis has begun.
Basal body assembly in developing zygospores occurs close to the plasma membrane (in the absence of pre-existing basal bodies) via an intermediate stage consisting of nine single A-tubules surrounding a central ‘cartwheel’. Assembly is similar in vegetative cells (and occurs prior to cell division), except that new basal bodies are physically attached to old ones by amorphous material. In vegetative cells, amorphous disks, which may possibly be still earlier stages in basal-body development occur in the same location as 9-singlet developing basal bodies. After the 9-singlet structure is formed, B and C fibres are added and the basal body elongates to its mature length. Microtubular roots, striated connexions and flagella are then assembled. Both flagellar regression and growth are gradual and sequential, the transitional region at the base of the flagellum being formed first and broken down last. The presence of amorphous material at the tip of the axoneme of growing and regressing flagella suggests that the axoneme grows or shortens by the sequential assembly or disassembly at its tip.
In homogenized cells basal bodies remain firmly attached to each other by their striated connexions. The flagellar transitional region, and parts of the membrane and of the 4 micro tubular roots, also remain attached; so also do new developing basal bodies, if present. These structures are well preserved in homogenates and new fine-structural details can be seen.
These results are discussed, and lend no support to the idea that basal bodies have genetic continuity. It is suggested that basal body development can be best understood if a distinction is made between the information needed to specify the structure of a basal body and that needed to specify its location and orientation.
The subcellular distribution of prolyl hydroxylase determined immunohistochemically
Authors: Al-Adnani M. S. , Patricko R. S. , McGEE D. 
Published: April 2021

ABSTRACT
The subcellular distribution of prolyl hydroxylase was determined in rat fibroblasts and chondrocytes immunohistochemically. After fixation in 4% paraformaldehyde fibroblasts were treated with a specific goat antiscrum to rat prolyl hydroxylase followed by rabbit anti-goat IgG conjugated with horseradish peroxidase. After further fixation in glutaraldehyde the bound intracellular peroxidase activity was identified by a standard histochemical procedure. Electron microscopy of the final product showed that the antigen was located only on the membranes of the rough endoplasmic reticulum. From ultracentrifugation analysis of fibroblast homogenates 80% of the prolyl hydroxylase activity could be located in the microsomal fraction. These observations suggest that not only collagen chain synthesis but also proline hydroxylation occurs on the membranes of the rough endoplasmic reticulum.
Rifampicin inhibition of the plastid rRNA synthesis of Marchantia Polymorpha
Authors: Loiseaux S. , Mache R. , Rozier C. 
Published: April 2021

ABSTRACT
The effect of rifampicin on the synthesis of plastid rRNA in Marchantia polymorpha was studied in vivo. As bacterial rRNA and plastid rRNA have the same electrophoretic mobilities, this study was possible only after a method for inhibiting bacterial contamination was developed. It was established that 91–100% of the rRNA synthesized by cultures of bacteria from Marchantia, after a labelling period of 3 and 9 h by 32P, is inhibited by 10 μg/ml of rifampicin. The same inhibition was observed when Marchantia was labelled for 3 h in the presence of 10 μg/ml of rifampicin, showing that no plastid rRNA was synthesized under out conditions, but only bacterial RNA. However, when labelling was continued for 9 h two important peaks of rRNA (23 and 16 s) were labelled in the presence of 10 or 20 μg/ml of rifampicin. These peaks are of chlorophastic origin as confirmed by the following facts: the labelling is light-activated; plastids isolated from thalli labelled for 12 h also show these two radioactive peaks. Cytoplasmic rRNA is synthesized under certain conditions. The synthesis of plastid rRNA is inhibited by higher concentrations of rifampicin, a concentration of 250 μg/ml producing at least 75% inhibition. Marchantia, a primitive multicellular plant, differs in this respect from higher plants, which seem to be, in most cases, insensitive to rifampicin.
Kinetic aspects of synchrony in suspension cultures of acer Pseudoplatanus L.
Authors: Gould A. R. , Street Η. E. 
Published: April 2021

ABSTRACT
Synchronous divisions have been induced in cell suspension cultures of sycamore (Acer pseudoplatanus L.) initiated at low density from stationary phase, nitrate-starved cells. The pattern of division and DNA replication synchrony is unusual in that it does not show progressive decay but rather a sharp transition to asynchrony. Feulgen densitometry data indicate that in terms of an S-phase synchrony index, DNA replication becomes more highly synchronized as cell density rises and interphase duration is reduced. In comparison with asynchronous cultures the duration of mitosis appears to be reduced during synchronous growth. The persistence of division and S-phase synchrony and the apparent shortening of interphase and mitosis in these sycamore cultures suggests the operation of intercellular entrainment. The departure from synchrony during the interphase which precedes initiation of asynchronous division remains unexplained.
X-ray microanalysis of the mid-gut epithelium of the fruitfly Drosophila Melanogaster
Authors: Tapp R. L. 
Published: April 2021

ABSTRACT
The cells in the mid-gut epithelium of Drosophila melanogasler which accumulate copper were examined by X-ray microanalysis. Both wavelength dispersive and energy dispersive analyses were used. The copper was located in granules 0.3−1.0μm in diameter which were bounded by membranes and similar, morphologically, to secondary lysosomes. The copper was associated with high concentrations of sulphur but no other elements with an atomic number greater than 9 (the lower limit of the analysis equipment) were present in appreciable concentrations.
Effects of discrete nuclear u.v.-microbeam irradiation on herpes virus and sv4o infection
Authors: Deák I. I. , Defendi V. 
Published: April 2021

ABSTRACT
The requirement for a nucleolus in the expression of structural genes of nuclear viruses was examined by means of experiments in which the nucleolus or other parts of the nucleus were inactivated by a microbeam of ultraviolet light. These experiments showed that the expression of such genes is not dependent on nucleolar function. This conclusion is discussed in the light of previous experiments in which similar inactivation of the nucleolus was shown to prevent the expression of cellular structural genes.
Proteins of the newt oocyte nucleus: Analysis of the nonhistone proteins from lampbrush chromosomes, nucleoli and nuclear sap
Authors: Maundrell K. 
Published: April 2021

ABSTRACT
An electrophoretic analysis has been carried out on the total protein of lampbrush chromosomes, nucleoli and nuclear sap, obtained from newt oocyte nuclei. In each case, distinctive and heterogeneous banding patterns are observed. The absence of detectable quantities of histones in oocyte chromatin is noted. In the case of the lampbrush chrómosome preparation, it is concluded that all protein species are derived from the ribonucleoprotein matrix of the lateral loops.
An ultrastructural study of the spermatozoid of the fern, Marsilea vestita
Authors: Myles Diana Gold , Bell P. R. 
Published: April 2021

ABSTRACT
The ultrastructure of the mature spermatozoid of Marsilea vestita was studied after its release from the microspore and prior to its penetration of the egg. The spermatozoid is a pearshaped cell with a complex spiral structure coiled around the edge in the narrow anterior end. This coil is composed of a large mitochondrion, elongated nucleus with highly condensed chromatin, a ribbon of microtubules, and a dense band of material (flagellated band) into which the flagella are inserted. There are over a hundred flagella protruding from each spermatozoid along the length of the coil. At the anterior tip of the coil is a short multilayered structure. It is not known what maintains the helical shape of the coil. The microtubular ribbon could be involved, but it is also possible that either the flagellated band, the condensed chromatin, or both, are sufficiently rigid to retain their shapes unaided.
When the spermatozoid is first released from the microspore it includes a cytoplasmic vesicle in the posterior region containing plastids, mitochondria, and other organelles. This vesicle is shed, taking the nuclear envelope with it, before the spermatozoid reaches the egg.
Cytoplasmic streaming in Chara: A cell model activated by atp and inhibited by cytochalasin b
Authors: Williamson R. E. 
Published: April 2021

ABSTRACT
After vacuolar perfusion of Chara internode cells, the cytoplasm remaining in situ can be reactivated by ATP to give full rates of streaming. Observations during both perfusion and reactivation indicated that the generation of the motive force was associated with fibres consisting of bundles of microfilaments. In the absence of ATP, the remaining endoplasmic organelles were immobilized along such fibres. When ATP was introduced, organelles moved along the fibres at speeds up to 50μms−1, but were progressively released from contact to leave the fibres in a conspicuously clean state. Inorganic pyrophosphate freed the organelles from the fibres without supporting movements. Motility required millimolar Mg2+ levels, free Ca2+ at 10−7 M or less and was inhibited by high levels of Cl− and by pH’s on either side of 7·0. The reactivated movements were rapidly and completely inhibited by 25 μ ml−1 cytochalasin B. The results are interpreted in terms of actin filaments in the stationary cortex interacting with a myosin-like protein which is able to link to endoplasmic organelles. Movement results from an active shear type of mechanism.