bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ciliary activity of cultured rabbit tracheal epithelium: beat pattern and metachrony
Authors: Sanderson M. J. , Sleigh M. A. 
Published: April 2021

ABSTRACT
The beat pattern of rabbit tracheal cilia has been investigated using high-speed cine photography and scanning electron microscopy, on cultured epithelia of known orientation.
The cilia normally rest in the position reached at the end of the effective stroke, the ciliary tips pointing towards the oropharynx. Each beat begins with a recovery (or preparative) stroke in which a bend is propagated up the cilium causing the cilium to rotate backwards in a clockwise sweep, as viewed from above. At the end of its recovery stroke the cilium progresses immediately into the effective (or power) stroke, which is almost planar and in a cephalad direction. The active cilium describes an arc of almost 110° before reaching the rest stage. This beat pattern is not significantly altered over an increase in frequency from 13 –29 Hz; the relative durations of the 2 active phases of the beat remain similar over this range.
Metachronal waves exist in the form of short erratic areas of coordinated beating which travel only short distances. Within each area, the non-planar recovery strokes initiate an antilaeoplectic wave of activity which recruits inactive cilia to extend the wave. As cilia perform their effective strokes, adjacent cilia in the plane of beating move in an antiplectic sequence. This pattern of coordination is related to the pattern of beat of the cilia and their distribution on the epithelium.
Infiltration of tumour cells into cultures of isolated hepatocytes
Authors: Roos Ed , Van De Pavert Ilja V. , Middelkoop Otto P. 
Published: April 2021

ABSTRACT
MB 6A lymphosarcoma and TA3 mammary carcinoma cells have previously been shown to infiltrate from liver blood vessels, where they had been arrested, into the liver parenchyma. The same tumour cells were presently added to cultures of isolated hepatocytes, 24 h after their isolation.
Both tumour cell types adhered to both dorsal and lateral surfaces of hepatocytes. The lymphosarcoma cells rapidly infiltrated between the hepatocytes. They first extended pointed pseudopods between the liver cells, and when the tumour cell body intruded, they deeply invaginated the liver cells at an interhepatocyte boundary. The MB 6A cells accumulated between and under the hepatocytes, and after 24 h virtually all cells were contained within the cultures.
TA3 cells also invaginated hepatocytes, not only at interhepatocyte boundaries, but all over the exposed surface. They did not extend pseudopods. The process was much slower than with MB 6A cells: After 24 h a few TA3 cells were completely encircled by hepatocytes. These observations indicate that the mechanism of infiltration is different for the 2 tumour cell types.
Part of the TA3 cells did not invaginate the hepatocytes. Several of these cells spread on the hepatocyte surface, attaining a flattened shape.
TA3 cells formed extensive tight junctions with the hepatocytes, sometimes sealing an intercellular lumen that resembled both a tumour acinus and a bile canaliculus. Also desmosomes were occasionally formed.
The hepatocyte cultures appear to be a suitable model for studying the mechanism of liver infiltration, not only of tumour cells, but also of leucocytes.
Tentacle contraction in glycerinated Discophrya collini and the localization of HMM-binding filaments
Authors: Hackney Carole M. , Butler R. D. 
Published: April 2021

ABSTRACT
The contractile tentacles of the suctorian Discophrya collini contain a central microtubular axoneme as well as filamentous structures in the cortical epiplasm and in a fibrous collar around the axoneme at the tentacle base. The nature and possible roles of these components has been investigated by the use of reactivatable glycerinated cells. In these a mean tentacle contraction to 70 % of the original length could be achieved by a 5-min treatment with a reaction mixture containing ATP, calcium and magnesium ions, the same treatment giving retraction to 30 % in living cells. Both the microtubules of the axoneme and the filaments of the fibrous collar and epiplasm were present in the glycerinated cells, suggesting that these components consist of large water-insoluble molecules. The addition of heavy meromyosin to whole glycerinated cells resulted in the appearance of 36 –50-nm spaced ‘tails’ or filaments attached to the epiplasmic fibres and the aggregation of 3 –6-nm filaments and electron-dense material in the region of the fibrous collar. Neither of these 2 features was apparent after treatment with ATP. It is suggested that actin-like filaments are localized in the region of the fibrous collar and in the epiplasm, and that these are involved in tentacle retraction; whilst the microtubules of the axoneme are concerned with feeding, and play only a cytoskeletal role in the contractile mechanism.
The relationship between nuclear DNA content and centromere volume in higher plants
Authors: Bennett M. D. , Smith J. B. , Ward J. , Jenkins G. 
Published: April 2021

ABSTRACT
The total volume of centromeres per nucleus varies widely within Triticum aestiium cv. Chinese Spring (7-fold) and between 11 higher plant species (24-fold). Such variation is closely correlated with nuclear DNA content, nuclear volume and, to a lesser extent, the total volume of nucleoli per nucleus. Centromere volume reflects minor intraspecific developmental fluctuations in nuclear size independent of variation in nuclear DNA content, but variation in nuclear DNA plays the major role in determining centromere volume. Thus, in general a given total volume of centromeric material is apparently characteristic of an approximately constant nuclear volume and mass of nuclear DNA, but largely independent of chromosome number. The range of volumes of single centromeres in 4 taxa corresponds with the ranges of their single chromosome lengths or chromosome DNA contents. The centromere is, therefore, not a unit structure of constant size and mass but a chromosome segment whose highly variable volume closely reflects the volume and mass of the chromosome to which it belongs. The correlation between centromere size and chromosome size and DNA content is potentially useful for identifying single centromeres in unsquashed interphase and dividing nuclei; thereby facilitating studies of the intranuclear disposition of chromosomes.
The present results for centromeres provide probably the first example to indicate that variation in the total DNA content of small segments present on each chromosome sometimes varies directly in proportion to large interspecific variation in nuclear DNA C-value.
The close correlation between centromere volume, and nuclear DNA content is probably nucleotypic in origin. The functional significance of the variation in centromere volume is unknown, as is the nature of the mechanism which determines that centromere volume closely reflects nuclear and chromosome size and mass.
Surface changes during retraction-induced spreading of fibroblasts
Authors: Chen Wen-Tien 
Published: April 2021

ABSTRACT
Retraction of the trailing edge of an embryonic chick heart fibroblast results in an abrupt increase in protrusive activity at the leading edge of the cell. This increase was studied with time-lapse cinemicrography and scanning electron microscopy. Increased spreading following retraction results primarily from an increase in the duration of the extension phase of lamel-lipodial spreading. Much ruffling accompanies this increased spreading, particularly during its earliest phase. Upon retraction of the trailing edge, folds appear on the surface of the retracted tail and adjacent cell body and, soon after, microvilli-like structures appear as well. Once the moving cell has fully rcspread, however, the upper surface is once again smooth and free of folds and microvilli. Artificial detachment of a spreading lamella with a microneedle, and its consequent retraction, also causes increased protrusive activity of the remaining lamellae of the cell. These results are consistent with the hypothesis that retraction of one part of the cell makes surface membrane and cvtoplasm available for forming protrusions elsewhere.
5-hydroxytrypt amine-stimulated mitochondrial movement and microvillar growth in the lower malpighian tubule of the insect, Rhodnius prolixus
Authors: Bradley J.Timothy , Satir Peter 
Published: April 2021

ABSTRACT
Rapid initiation of ion transport occurs in the lower Malpighian tubule of the insect Rhodnius prolixus following feeding in vivo or stimulation with 5-hydroxytryptamine (5-HT) in vitro. Using the electron microscope, we have conducted a morphometric analysis of cells in the lowest one-third of the lower tubule, demonstrating that 5-HT also induces mitochondrial movement and microvillar growth simultaneously with, but independent of, the onset of ion transport.
Mitochondria move from a position below the cell cortex to one inside the microvilli within 10 min of stimulation with 5-HT, resulting in an 8- to 10-fold increase in the volume of mitochondria within the microvilli. Previous findings indicated that mitochondrial movement is dependent on actin-containing microfilaments, but not microtubules. As the mitochondria enter the microvillus, the core microfilaments are reorganized into a sheath of microfilaments, which extends closely parallel to the outer mitochondrial membrane down into the cell interior. This sheath of microfilaments is also observed around mitochondria in the axopods. We suggest that the core microfilaments are responsible for mitochondrial movement into the microvilli and axopods. Stimulation with 5-HT induces a shift in mitochondrial configuration from orthodox to condensed, indicating a possible increase in oxidative phosphorylation. Following stimulation, the microvilli grow about 3 × in volume and 2·5 × in surface area. These increases are more than can be accounted for by mitochondrial invasion and must involve the addition of new membrane and microfilament polymerization. The observed changes - microvillar growth, insertion of additional membrane, activation and movement of mitochondria adjacent to the ion transport membrane - are described in the light of their significance in ion transport. A simple model is proposed which unifies the observed ultrastructural changes and known ion movements in the lower tubule.
Binding of parbendazole to tubulin and its influence on microtubules in tissue-culture cells as revealed by immunofluorescence microscopy
Authors: Havercroft J. C. , Quinlan R. A. , Gull K. 
Published: April 2021

ABSTRACT
We have shown that the benzimidazole carbamate, parbendazole, is a potent inhibitor of microtubule assembly in vitro and in vivo. Radiolabelled parbendazole was shown to bind to purified tubulin. Immunofluorescence studies using an antitubulin antibody showed that parbendazole effectively depolymerizes cytoplasmic microtubulues in animal cells leaving only one or two microtubules associated with one centriole. The usefulness of parbendazole and other benzimidazole carbamates as inhibitors of microtubule functions is discussed.
Binding of isovaleraldehyde, an attractant, to zoospores of the fungus Phytophthora palmivora in relation to zoospore chemotaxis
Authors: Cameron J. Neil , Carlile Michael J. 
Published: April 2021

ABSTRACT
The interaction of isovaleraldehyde, an attractant, with zoospores of the fungus Phytoph-thora palmivora was investigated by using binding techniques. The amount of isovaleraldehyde bound diminished with time, an effect that may be related to sensory adaptation. In addition to non-specific binding, specific and saturable isovaleraldehyde binding was demonstrated. Cooperativity occurred at intermediate but not at low and high ligand concentrations. [3H] isovaleraldehyde was displaced by unlabelled isovaleraldehyde and by a number of chemically related ligands known to be chemotactic agents. Their dissociation constants as calculated from the displacement experiments paralleled their potency as attractants and it is suggested that these attractants act through the same receptor. Some other chemotactic agents did not displace [3H]isovaleraldehyde, and these presumably act through one or more other receptors.
Modification of fibroblast surface amines alters receptor-mediated cell spreading on protein-coated substrata but not adsorptive endocytosis
Authors: Aplin J. D. , Hughes R. C. 
Published: April 2021

ABSTRACT
Fluorescein isothiocyanate (FITC) and other anionic reagents specific for amine groups have previously been shown to inhibit the adhesion and spreading of cultured fibroblasts to fibronectin-coated surfaces (Butters, Devalia, Aplin & Hughes, 1980). Here it is demonstrated that a population of FITC-labelled cells can be separated using flow cytometry into fractions displaying greater and lesser adhesivity at lower and higher fluorescence, respectively, demonstrating that the inhibition is dose-dependent. Glass coverslips covalently derivatized with the lectins ricin and concanavalin A are used to show that the inhibition also occurs in lectin-mediated cell adhesion as well as in adhesion to collagen coated with fibronectin and plastic coated with serum or antibody, suggesting that all of these responses share a common, F1TC-sensitive component.
Simple primary amine compounds inhibit adhesion to fibronectin, but specific inhibitors of transglutaminases do not affect the process. Transglutaminase activity of cell surfaces has been implicated in protein endocytosis and receptor recycling (Davies et al. 1980).
FITC modification of cells appears to affect specifically adhesive interactions, since ricin cytotoxicity and infection of cells with influenza and Sendai viruses (phenomena thought to proceed by means of receptor-mediated endocytosis) are unaffected. Evidently, receptor-mediated cell attachment, spreading on protein-coated surfaces and protein endocytosis are functionally separate events requiring different cell-surface membrane components, even when the same protein (ricin) is used to trigger these 2 processes.
Mechanisms of nutritive endocytosis i. phagocytic versatility and cellular recognition in Chlorohydra digestive cells, a scanning electron microscope study
Authors: Mcneil Paul L. 
Published: April 2021

ABSTRACT
The quantity of surface membrane internalized during phagocytosis by Chlorohydra digestive cells was estimated for a range of particle types. Challenge with 2 of these particles, freshly isolated symbiotic algae (FIS) and latex spheres (LS), resulted in a greater (2·5 ×) quantity of surface membrane interiorized than with heat-treated symbiotic algae (HTS) and free living algae (FA), Chlorella vulgaris. This discriminatory process was investigated further by a scanning electron microscope (SEM) and transmission electron microscope (TEM) comparison of the surface events associated with phagocytosis of each of these 4 particles. Those particles that were avidly phagocytized, FIS and LS, were both enveloped by a tightly fitting extension of digestive-cell surface, and obtained a prominent surface coating after their injection into the gut of Chlorohydra. Phagocytic challenge with FIS resulted, furthermore, in the rapid formation of a dense microvillar cover on digestive-cell surfaces. HTS and FA, on the other hand, were enveloped by a less closely fitting extension of digestive-cell surface, did not obtain a prominent surface coating, and did not induce the formation of microvilli. In addition, SEM revealed that at least 3 morphologically distinct phagocytic modes were utilized by the versatile nutritive phagocyte of Chlorohydra’. (1) envelopment by the progressive movement of numerous, overlapping tubular protrusions (microvilli) over the particle (FIS) surface, forming first a network of tubular interlocking members, and finally a continuous but rough enclosing surface; (2) envelopment by a single, smooth-surfaced, funnel-like extension of digestive-cell surface (FIS, LS, HTS, FA); and (3) envelopment by multiple, broad folds, often of unequal size, and with overlapping margins (Artemia particles).
The centriolar complex isolated from starfish spermatozoa
Authors: Kuriyama Ryoko , Kanatani Haruo 
Published: April 2021

ABSTRACT
Centrioles from spermatozoa of the starfish, Asterina pectinifera, were isolated and partially purified by solubilization of chromatin followed by sucrose density-gradient centrifugation. The ultrastructure of the isolated centriolar complex was investigated in whole mount preparations by electron microscopy. The complex unit was composed of a pair of centrioles and a pericentriolar structure, which associated with the distal end of the distal centriole by 9 spokelike satellites extending radially to a marginal ring. Each satellite bifurcated at a dense node forming 2 fan-like shapes with a periodic striated pattern. The tubular structure of the centrioles easily disintegrated, leaving the pericentriolar structure or axonemal microtubules intact.
The distal centriole in a spermatozoon served as an initiating site for flagellar microtubule assembly; that is, a number of ‘9 + 2’ axonemal tubules were observed adhering just beneath the distal end of the basal body. In experiments in vitro, polymerization of microtubule proteins purified from porcine brain was initiated by the structure at the ends of both proximal and distal centrioles, but not from the satellites or the marginal ring. Also, few if any microtubules were formed from the sides of each centriole, even in the presence of a high concentration of exogenous tubulin. On the other hand, centrioles of spermatozoa, when they were in mature ooplasm, could initiate the formation of sperm asters by microtubules. Therefore, centrioles in spermatozoa seem to be able to initiate microtubules in 2 ways. A possible explanation of the difference between the 2 types of microtubule organization in vivo, i.e. in the sperm cell itself and in the ooplasm, is discussed.
Heterocyst differentiation and cell division in the cyanobacterium Anabaena cylindrical effect of high light intensity
Authors: Adams David G. , Carr Noel G. 
Published: April 2021

ABSTRACT
Heterocyst differentiation in the cyanobacterium Anabaena cylindrica is initiated by the removal of fixed nitrogen from the medium. These specialized cells occur singly at regular intervals within filaments of vegetative cells. Incubation of cultures for periods of up to 12 h immediately prior to or following removal of fixed nitrogen, at a light intensity (500 μEinsteins cm−2 s−1) approximately 10-fold higher than that required for optimum growth, resulted in the differentiation of pairs of adjacent (double) heterocysts. The frequency of double heterocysts was proportional to the length of the period of high light intensity. During growth at normal light intensity approximately 5% of cell divisions were symmetrical, but this increased more than 3-fold during 10-h incubation at high light intensity. The frequency of dividing cells remained constant during this period, but increased rapidly on return to normal light. The frequency of double heterocysts was reduced if a period of incubation at normal light intensity was interposed between the 12-h period at high light intensity and transfer to nitrogen-free medium. A period of 8 h normal light was required to reduce the frequency of double heterocysts to control values, and this corresponded to the length of time needed for the frequency of symmetrical divisions to return to control levels following 12 h at high light intensity. We confirm that cell division in Anabaena cylindrica is asymmetrical and conclude that the presence of double heterocysts results from an increase in the symmetry of cell division during incubation at high light intensity. The results also support the finding of previous workers that a cell is only susceptible to differentiation during a short period following its formation. During the period of high light the rate of doubling of the absorbance of the culture at 750 mn increased from 24 h to approximately 10 h and decreased to more than 100 h on return to normal light. The very high rate could be explained by increases in the volume and granular content of cells during incubation at high light intensity and did not represent an equivalent increase in the rate of cell division.
Nuclear cycle of Saprolegnia ferax: I. Brent Heath
Authors: Rethoret Karen 
Published: April 2021

ABSTRACT
The mitotic nuclear (equivalent to cell) cycle of the oomycete fungus, Saprolegnia ferax, was analysed by quantitative serial-section electron microscopy of hyphal nuclear populations synchronized by inhibition of DNA synthesis by fluorodeoxyuridine (FdUrd). Following telophase and karyokinesis, kinetochore mitrotubules persist into G, stage as a single group of ∼ 42 per nucleus (an = 42 for this species). During G1 the centrioles replicate and kinetochore microtubules separate into 2 groups of ∼ 21, a configuration they retain through S and G2,. During metaphase a new population of kinetochore microtubules are formed, each one of an amphitelic pair connecting to the opposite pole to that associated with the persistent microtubule from the previous division. Thus, by the end of metaphase, there are ∼ 42 kinetochore microtubules per half spindle. FdUrd, applied for 2 h with uracil, completely blocks DNA synthesis yet permits centriole replication and causes nuclei to accumulate with 2 pairs of centrioles, 2 arrays (each of 21) of kinetochore microtubules, and apparently enlarged nucleoli. Removal of FdUrd permits rapid (within 30 min) DNA synthesis followed by successive rounds of decreasingly synchronous nuclear cycles. These post-FdUrd cycles are 25 times longer than normal at 2·5 h, with S plus G2 being more extended than other phases. Calculated durations of a normal nuclear cycle are: G1, 33 min; S, 7 min; G2, 10 min; metaphase, 8 min; anaphase, 0·5 min; and telophase, 4 min.