bluuebunny/crossref_metadata_2025 huggingface dataset:
Limpet haemocytes: II. The role of spikes in locomotion and spreading
Authors: Partridge T. , Davies P. S.
Published: April 2021

A new preparation for the study of cell spreading and locomotion was investigated, using time-lapse cinemicrography and photomicrography. The preparation of limpet haemocytes has the advantage of being a natural one, not derived by tissue dissociation, and is functional at normal laboratory temperatures.

The commonest cell type, the amoebocytes, have numerous spikes, up to 15 μm in length, which project from their surface, carry lamellar extensions between them, and run deep into the cytoplasm. In the spread cell this spike-supported lamella constitutes the margin of the cell, resulting in a crenate appearance. The extensions have the properties of lamellipodia, and spreading and locomotion both occur by extension, first of spikes then lamella. It is suggested that the direction of movement may be regulated by the spikes. Contact inhibition of movement is accompanied by disappearance of the spikes in the region of contact between cells and production of spikes in other regions which lead the cells away from the contact.

Spreading of cells from large aggregates of amoebocytes entails rapid centrifugal locomotion of the peripheral cells which is thought to be a consequence of contact inhibition. However, there also appears to be an opposing influence which largely prevents complete loss of contact between cells, resulting in an epithelioid morphology in a spread culture.

Amoebocytes are not adhesive to the substrate in Ca1+ and Mg2+-free (CMF) conditions but rapidly regain adhesiveness and spread normally on addition of either divalent cation to the concentration normally found in seawater. Spikes and lamellae are produced in CMF conditions but do not spread on to the substrate and do not show their normal reactions to contact with other cells.

Macrophages spread as disks of gradually increasing diameter without the aid of spikes but with the formation of conspicuous ruffle-like thickenings. Once fully spread they become quiescent and show little or no further ruffling and undergo no significant locomotion. The attachment and spreading of these cells was found to be independent of the presence in the medium of divalent cations.
The accessibility of a developing lepidopteran nervous system to lanthanum and peroxidase
Authors: McLaughlin Barbara J.
Published: April 2021

The accessibility of the nervous system of Manduca sexta to horseradish peroxidase and lanthanum during metamorphosis has been studied. In the fifth instar larva, peroxidase penetrates the thick neural lamella but does not reach the perineurium. In the first week after larval-pupal ecdysis, when the intercellular channels between hypertrophied perineurial I cells are the least tortuous, the enzymic tracer bypasses the perineurial I tight and gap junctions and penetrates as far as the perineurial II bracelet layer. During this time, there is active uptake of peroxidase by the perineurial I cells but no reaction product is found in the underlying perineurial II cell bracelet. In the second week after larval-pupal ecdysis, when the perineurium is a flattened interdigitating cell layer, peroxidase does not penetrate as far as the perineurial I and II interspace and there is little or no uptake of the protein by the perineurial I cells. Lanthanum, in contrast, passes the perineurial I tight and gap junctions, which are presumed to be macular, and travels within the entire perineurial I and II interspace throughout metamorphosis. As it travels within this interspace, it gains access to the perineurial II bracelet connexions, which differ in their ability to restrict lanthanum. Lanthanum is able to penetrate the entire overlapping connexion with its predominant gap junctions before being stopped, but penetrates the more complex interdigitating connexion with its extensive tight, gap and septate junctions for only a short distance. The relevance of the perineurial II bracelet layer and its intercellular connexions to the maintenance of a blood-brain barrier in this developing nervous system is discussed.
Effect of near ultraviolet and visible light on amoeba
Authors: Chatterjee S. , Bhattacharjee S. K.
Published: April 2021

The near ultraviolet and visible light (VL) impinging at an intensity of 2·5 × 102 J s−1 m−s for 2·5 h kills the mitotic and the early 5-phase (0- to 15-min-old) amoebae. At the mid- and late S-period only a fraction of cells are killed by VL and the G2 phase cells are quite resistant. Amoebae of all cell cycle stages show a delay in the first mitotic division. DNA synthesis, as measured by [3H]thymidine incorporation, is depressed in the VL-exposed early-S amoebae. A concurrent but temporary inhibition in [3H]leucine incorporation also occurs in these cells. However, no significant change in [3H]uridine incorporation has been found.

To localize the site of lethal damage, nuclear transplantation studies were undertaken between the control amoebae and the amoebae treated with VL. The nucleus of a VL-exposed early S-phase cell recovers when transplanted immediately after VL exposure into an enucleate G2 cytoplasm but dies if grafted into an enucleate S-phase cytoplasm. The therapeutic effect of the G2 cytoplasm, although at a lower level, is also evident even when the treated early S-phase nucleus is implanted 20 h later, but not after 48 h, into the G2 cytoplasm. The amoeba cytoplasm shows resistance to VL-irradiation, can accept a control nucleus from any cell cycle stage, and function normally. The G, nucleus also remains apparently unaffected to VL exposure and can survive when it is transferred to the control cytoplasm of any cell-cycle phase. All these findings are discussed in the light of the possible existence of a repair system against VL-induced damage in the G2-phase amoeba.
Cell density dependence of the aggregation characteristics of the cellular slime mould Dictyostelium discoideum
Authors: Hashimoto Y. , Cohen M. H. , Robertson A.
Published: April 2021

We have measured fruiting body density and spore formation efficiency in Dictyostelium discoideum as functions of initial cell density. Experiments were performed on agar made up with distilled water and on buffered agar. Minor differences are seen; these are discussed. The functions show 4 regions of density dependence which can be accounted for by changes in aggregation characteristics with density and changes in the efficiency of spore differentiation. The results are discussed in terms of the relaying mechanism for signal propagation controlling cell aggregation. They extend earlier measurements by Bonner & Dodd and by Hohl & Raper, supply data for a quantitative model of the aggregation process, allow estimates of signal range, and show the importance of entrainment between neighbouring centres in defining aggregation territories.
Selective In vivo damage by ‘visible’ light of brdu-containing mitochondrial dna in a thymidine kinase-deficient mouse cell line with persistent mitochondrial enzyme activity
Authors: Croizat B. , Attardi G.
Published: April 2021

The selective incorporation of 5-bromodeoxyuridine (BrdU) into mitochondrial DNA (mit-DNA) in the LM(TK−) Cl1D cell line, a thymidine kinase-deficient derivative of L fibroblasts with persistent mitochondrial enzyme activity, has been utilized to specifically damage mit-DNA by ‘visible’ light irradiation. (‘Visible light’ indicates the source of light used, although the components most active photochemically on BrdU-substituted DNA are in the near-visible range, 300–340 nm.) (Szybalski & Opara-Kubinski, 1965).

LM(TK−) Cl 1D cells, which had been grown in the presence of 30 μg/ml BrdU, were irradiated with ‘visible’ light. Analysis of the pre-existing mit-DNA in these cells, which had been long-term labelled with [5-3H]deoxycytidine, showed a progressive decrease, with increasing duration of irradiation, in the proportion of the closed-circular form and an increase in that of the open-circular form of mit-DNA, with the subsequent appearance of fragments of this DNA. Furthermore, there was a decrease during irradiation in the total amount of mit-DNA, which became about 35 % of the non-irradiated control after 65 h irradiation. On the other hand, irradiation with ‘visible’ light failed to cause any quantitative or qualitative change, with respect to the non-irradiated control, in mit-DNA from cells grown in the absence of BrdU and long-term labelled with [Me-3H]thymidine.

An analysis of the incorporation of [5-3H]deoxycytidine into mit-DNA of BrdU-grown cells, during a 3-h exposure of the cells to the precursor following irradiation, showed a fairly rapid decline of mit-DNA labelling; this became about 50% of the non-irradiated control after 12 h irradiation, decreasing to about 25% in the next 48 h. By contrast, no effect of irradiation was observed on the subsequent pulse-labelling of mit-DNA with [Me-3H]thymidine in cells grown in the absence of BrdU. Furthermore, no change in the size of the extracted nuclear DNA was found in irradiated BrdU-grown cells.

The progressive and selective damage and destruction of mit-DNA during irradiation with ‘visible’ light of Cl 1D cells correlate fairly well with the kinetics of loss of cell viability occurring under the same conditions, as described in the accompanying paper, strongly suggesting a link between the two phenomena.
Studies on the function and composition of the 10-nm(100- å) filaments of vertebrate smooth muscle
Authors: Small J. V. , Sobieszek A.
Published: April 2021

The extraction of isolated vertebrate smooth muscle cells at high and low ionic strength yields cell ghosts which are seen in the electron microscope to be composed of a complex network of 10-nm filaments, together with residual actin. After SDS-gel electrophoresis of the cell ghosts only 2 bands may be recognized, one corresponding to actin and the other migrating at about 55000 mol. wt that arises from the 10-nm filaments. The 10-nm filaments are extremely sensitive to proteolysis and are absent from cells exposed to crude collagenase in the presence of Triton X-100. Such cells, lacking 10-nm filaments, still contract in response to ATP. The data indicate that the 10-nm filaments are not essential for contraction, but rather form a specialized intracellular cytoskeleton.

While completely insoluble in concentrated salt solutions the 55000 mol. wt protein is readily extracted with acetic acid from homogenized and salt-extracted smooth muscle residue. The extracted protein reassembles, on dialysis, into filaments of about 10-nm diameter and has an amino acid composition almost identical to that deduced for vertebrate neurofilaments. From the cytoskeletal role that the 10-nm filaments play in smooth muscle and, as appears likely, in other cell types the filament protein has been tentatively termed ‘skeletin’. Results relating to the proportion of skeletin in smooth muscle and the structure of the 10-nm filaments are described and discussed.
The structure of syncytia induced by the phytoparasitic nematode Nacobbus aberrans in tomato roots, and the possible role of plasmodesmata in their nutrition
Authors: Jones M. G. K. , Payne H. L.
Published: April 2021

The structure of syncytia induced within galls in tomato roots by the false root-knot nematode Nacobbus aberrans has been examined by light and electron microscopy. A syncytium develops by breakdown of individual cell walls, which allows movement of cytoplasmic contents between transformed cells. The wall breakdown takes place at pit fields, where the plasmodesmata may be protected from digestion until the surrounding wall is removed. Numerous sieve elements differentiate in the cells outside the syncytium. These sieve elements, and also plasmodesmata in pit fields, are demonstrated by fluorescence microscopy. The possibility of a symplastic pathway of solute movement from the phloem to the syncytium is suggested. A massive accumulation of starch occurs in the gall cells and syncytial cells, which may be related to the proliferation of phloem. Wall ingrowths typical of transfer cells are absent, and a comparative survey of the structure and mode of solute entry into nematode-transformed cells in which ingrowths are present or absent is presented.
Hijacking of the host cell Golgi by Plasmodium berghei liver stage parasites
Authors: De Niz Mariana , Caldelari Reto , Kaiser Gesine , Zuber Benoit , Heo Won Do , Heussler Volker T. , Agop-Nersesian Carolina
Published: April 2021

The intracellular lifestyle represents a challenge for the rapidly proliferating liver stage Plasmodium parasite. In order to scavenge host resources, Plasmodium has evolved the ability to target and manipulate host cell organelles. Using dynamic fluorescence-based imaging, we here show an interplay between the pre-erythrocytic stages of Plasmodium berghei and the host cell Golgi during liver stage development. Liver stage schizonts fragment the host cell Golgi into miniaturized stacks, which increases surface interactions with the parasitophorous vacuolar membrane of the parasite. Expression of specific dominant-negative Arf1 and Rab GTPases, which interfere with the host cell Golgi-linked vesicular machinery, results in developmental delay and diminished survival of liver stage parasites. Moreover, functional Rab11a is critical for the ability of the parasites to induce Golgi fragmentation. Altogether, we demonstrate that the structural integrity of the host cell Golgi and Golgi-associated vesicular traffic is important for optimal pre-erythrocytic development of P. berghei. The parasite hijacks the Golgi structure of the hepatocyte to optimize its own intracellular development.

This article has an associated First Person interview with the first author of the paper.
A twelve-channel automatic device for continuous recording of cell aggregation by measurement of small-angle light-scattering
Authors: Thomas William A. , Steinberg Malcolm S.
Published: April 2021

We describe here a 12-channel aggregometer, evolved from the instrument described by Beug & Gerisch in 1972, which records the course of aggregation or agglutination of cells or other particles by following the changes in light-scattering of the aggregating suspension. The instrument incorporates a simple memory system for condensing the data, introduces an improved cuvette design, and can be adjusted in its responsiveness to light-scattering by particles of different sizes.

In our aggregometer, a vertical wheel in an opaque thermostatted chamber accommodates up to 12 cuvettes each containing a cell suspension and an air bubble. The constant rising of the bubble as the wheel rotates causes the stirring action which promotes aggregation. At a certain point in its rotational path, each cuvette is penetrated by a beam of light focused upon an absorbing beam stop centred in front of a photomultiplier tube. Particles suspended in the cuvette scatter a portion of the light beyond the beam stop into the photomultiplier tube to produce an electrical pulse proportional to the photon input. Collection of these pulses with the wheel in continuous motion avoids any disturbance of the course of aggregation. The pulses are routed to memory circuits for summation and eventual recording by a 12-channel printing potentiometer which automatically colour-codes and numbers each curve.

The cuvettes consist of 2 glass microscope coverslips affixed with silicone grease over a hole in a thin, stainless steel blank. They are very durable and are easily dismantled and reassembled for cleaning. The coverslips are replaced after each use. The discoid chamber of our cuvette permits uniform circulation of the bubble, which in turn causes gentle stirring of the aggregating suspension at a rate that is a direct and continuous function of rev/min.

Measurement of light-scattering at small angles (3–5·5°) provides great sensitivity to the disappearance of single cells and progressively less sensitivity to the coalescence of aggregates of progressively larger size. The signal generated by the photomultiplier tube decreases as aggregation proceeds.

At 32 rev/min, one data point per channel, representing the sum (average) of 24 successive measurements, is printed every 45 s. In the course of a 60-min assay under standard conditions, up to 23040 individual readings can be automatically taken, summed and plotted. In a comparison of 8 identical samples run simultaneously, the printed values after 60 min agreed with a standard deviation of ± 2 %.
In situ hybridization to lampbrush chromosomes: A potential source of error exposed
Authors: Callan H. G. , Old R. W.
Published: April 2021

Denatured 3H-labelled DNAs containing Xenopus or human globin sequences hybridize to RNA transcripts on a single pair of lateral loops on lampbrush chromosome IX of Triturus cristatns carnifex, and to no other loops on this chromosome or the rest of the complement. However they do so, not because of the globin sequences in the probes, but rather because the plasmids from which the probes were prepared were constructed with G.C homopolymer tails. Simple sequence poly d(C/G)n probes also hybridize with RNA transcripts on this same pair of loops, and with no others.
Cell proliferation and migration on collagen substrata in vitro
Authors: Schor Seth L.
Published: April 2021

Quantitative data are presented regarding cell proliferation and migration on (a) collagen films (b) the surface of 3-dimensional gels of native collagen fibres and (c) within the 3-dimensional collagen gel matrix, as part of a study of the effects of the extracellular matrix on cell behaviour. The nature of the collagen environment was found to influence the proliferation of certain cell types, but not of others. For example, HeLa cells proliferate at approximately the same rate and reach the same saturation cell densities on all of the collagen substrata, while human skin fibroblasts grow more slowly within the 3-dimensional collagen gel matrix compared with cells either on the gel surface or on collagen films. The 3-dimensional gels of native collagen fibres may also be used to study cell migration on the gel surface, as well as cell migration (or ‘infiltration’) from the gel surface into the 3-dimensional collagen matrix. Two methods have been used to obtain quantitative information concerning cell infiltration into the collagen gel, one involving the selective removal of cells from the gel surface, while the other relies on direct microscopic examination. Of the cells examined to date, epithelial cells (both normal and tumour) do not show infiltrative behaviour, while both normal and virally transformed fibroblasts, as well as tumour cells of non-epithelial origin (e.g. melanoma), do infiltrate into the collagen gel matrix, at rates which vary considerably according to cell type.
Clonal death associated with the number of fissions in Paramecium caudatum
Authors: Takagi Yoshiomi , Yoshida Michiko
Published: April 2021

Contrary to an earlier report suggesting clonal immortality in Paramecium caudatum, the clones of the same species in this study terminated inevitably with a maximal life-span of 658 fissions and showed, prior to clonal death, decreased fission rate, increased probability of the appearance of non-dividing or dead cells after cell division, and increased frequency of morphological abnormality and of division asynchrony. Clonal senescence and death after a limited number of fissions was reproducible even if subclones derived from the original clone of a known fission age were examined again after a lag of 468 days. These results indicate that clones of P. caudatum are mortal and that they use fissions, not days, to measure life-span. Possible causes for the discrepancies between the earlier report and the present one are discussed.
Ultrastructure of modified root-tip cells in Ficus carica, induced by the ectoparasitic nematode Xiphinema index
Authors: Wyss U. , Lehmann H. , Jank-Ladwig R.
Published: April 2021

The migratory ectoparasitic root nematode Xiphinema index, added to Ficus carica seedlings in. sterile agar culture, fed exclusively on the tips of the roots. As a response the tips started to swell and became transformed into terminal galls as long as feeding was continued.

When the cytology of swollen root-tips was examined 24 h after the first nematode attack, necrotic cells, scattered singly or in small groups within the root apex, were found in ultrathin sections. These cells, whose protoplasts showed features of a hypersensitive reaction, were most probably those fed upon by the nematodes. Each necrotic cell was surrounded by several enlarged, mostly binucleate cells with dense cytoplasm. One day later the binculeate cells were multinucleate, containing 4 or even 8 nuclei. The clear-cut demarcation between necrotic and modified cells indicated that only the stimulus for the induction of modified cells but not the stimulus for cell necrosis passed into neighbouring cells.

Root-tip galls that provided the appropriate food for egg production in nematodes contained greatly enlarged multinucleate cells between necrotic cells. The modified cells showed features of high metabolic activities, expressed in nuclear and nucleolar hypertrophy, invagination of the nuclear envelope, increased cytoplasmic density, abundance of mitochondria, plastids and rough endoplasmic reticulum. Wall ingrowths, typical of transfer cells, were rare and if present occurred only adjacent to necrotic cells. In older modified cells new cell plates, surrounded by phragmoplasts, were formed.
Euglena plasma membrane during normal and vitamin B12 starvation growth
Authors: Lefort-Tran M. , Bre M. H. , Ranck J. L. , Pouphile M.
Published: April 2021

Freeze-fracture and optical diffraction techniques were used to study the organization of the Euglena pellicle during the normal and replicative stages of the cell cycle and during vitamin B12 starvation. It was shown that the diffuse layer underlying the tripartite structure has a fibrillar structure. Despite the absence of homology in the 2 fracture faces of the pellicle, the EF striated and the PF particulate ones appear complementary as shown by optical diffraction studies; it must therefore be considered as a true membrane. The grooves are free from such particles and striations. They appear as a specific pattern of the cortex, different from the ridges in their structural organization and their replicative capacity as observed during vitamin B12 starvation. This notion is confirmed by the mode of pellicular growth which is characterized by 2 steps. The first occurs during the early replicative stage (pre-mitotic phase of the cell cycle) when the formation of a new ridge is correlated with the appearance of the ‘minor’ orientation of a 2-dimensional lattice on the EF and the PF faces and the spread of the particles over the PF face of the space between the old ridges. The second takes place during the lengthening of the ridges from the initiating posterior side (non-replicative stage).During this second step, the ‘major’ orientation of the lattice is preferentially observed in control cells and exclusively in starved cells.

The striking differences between the grooves and the ridges is discussed, as well as the 2 modes of growth and their significance in morphogenesis.
The nucleolus in telophase, interphase and prophase
Authors: Ashraf Mohammad , Godward M. B. E.
Published: April 2021

The ultrastructure of telophase to interphase has been followed in a green alga, Spirogyra submargaritata. A series of changes transitional between the late anaphase chromatid, the decondensing chromatid of telophase, and the ‘pale fibrillar material’ occupying channels in the nucleolus at interphase have been demonstrated. Early stages in the regeneration of the nucleolus are described.

It has been shown that the pale fibrillar material in the nucleolus is attached to, and continuous with, the fully condensed (chromocentric) part of the nucleolar-organizing chromosome at interphase. It is also shown that in early prophase, the channels in the nucleolonema of the nucleolus are no longer occupied by pale fibrillar material, but instead a long section of condensed chromosome is present, traversing the nucleolonema. It is contended that these observations taken together constitute evidence that the pale fibrillar material of the nucleolus is the chromatin of the nucleolar-organizing region of the chromosome, expanded for transcription.

A model of the nucleolus as it is seen in most electron-microscope sections, and as it can be interpreted in the light of present-day knowledge about it, is presented. A brief review of the relevant literature considers the views supporting the model, and the contrary views, implicating the use of the term ‘nucleolar organizer’, that are still current at the present time.
Nematocyte migration in hydra: evidence for contact guidance in vivo
Authors: Campbell Richard D. , Marcum Beverly A.
Published: April 2021

Nematocytes rapidly emigrate from normal tissue implanted into an epithelial hydra, which lacks its own nematocytes. We observed emigrating nematocytes, both in time-lapse movies and in fixed whole mounts, to learn what controls directionality. The cells migrate at speeds of 10—30μm/min with a pseudopod forward and the capsule trailing. Migration is aligned parallel to the polyp axis, but cells move both proximally and distally and often shuttle back and forth. Thus, migration is strongly bidirectional, with a slight distal bias since at any time more cells are moving towards the tentacles. Nematocytes freely migrate through tissue of reversed polarity. No evidence was found for a chemotactic stimulus emitted from the tentacles. The bidirectional movement pattern appeared to be imposed by epithelial muscle processes, which form an axial, fibrous mat on which nematocytes migrate. Experimental deformation of the muscle alignment results in a corresponding deformation of nematocyte migration. Thus, nematocyte migration appears to be bidirectionally oriented through contact guidance by epithelial muscle processes.
ATP-driven tubule extrusion from axonemes without outer dynein arms of sea-urchin sperm flagella
Authors: Hata H. , Yano Y. , Mohri T. , Mohri H. , Miki-Noumura T.
Published: April 2021

We have prepared axonemes without outer dynein arms from sea-urchin (Pseudocentrotus depressus, Hemicentrotus pulcherrimus) sperm flagella by selective solubilization with NaCl. Electron microscopy revealed that the axonemes gradually lost their outer arms in 0·5 M NaCl during 10 min. Such axonemes retained 42·8 ±7·3 % of their total axonemal ATPase activity and showed C, A, D and B bands in the dynein region of 4 % SDS-gel, while a solubilized fraction of the outer arms consisted almost entirely of A band polypeptide. We have succeeded in causing extrusion of the outer doublets from such axonemes by addition of ATP and trypsin. A bundle of outer doublets was sometimes observed to be extruded first from an axoneme and to show bending motion for a while, subsequently followed by a sliding of separate doublets past each other. The speed of the tubule extrusion process was slower and around 60 % of that of intact axonemes having both types of arm.

These observations indicate that the inner arms have a function equivalent to that of the outer arms, of sliding on adjacent doublets, although the inner arms seem to be constituted from polypeptide(s) different from that of the outer arms.
Structural responses of amoebae to the injection of heterologous cytoplasm
Authors: Flickinger Charles J. , Read Graham A. , Kabana Ellen M.
Published: April 2021

Responses to the introduction of heterologous cytoplasm and the fate of foreign organelles were investigated in amoebae. Heterologous cytoplasm was transferred by microinjection from Pelomyxa carolinensis to Amoeba discoides. In control experiments, homologous cytoplasm was transferred from one A. discoides to another. Recipient cells were observed by light microscopy, and samples were prepared for ultrastructural study at intervals between 15 min and 3 days after operation. Recipients of heterologous cytoplasm showed two main responses. First, about 40 % recipients expelled small amounts of cytoplasm by a blebbing process within 30 min after injection. Second, organelles were segregated and broken down in membrane-bounded cytoplasmic vacuoles between 6 h and 2 days after operation. Acid phosphatase reaction product was observed in these vacuoles along with altered organelles. Use of electron-dense thoria particles to mark donor cells demonstrated the presence of injected cytoplasm in the vacuoles. In contrast, when amoebae were injected with homologous cytoplasm, none was expelled and vacuoles containing degenerating organelles were uncommon. The survival rate and general appearance of recipients of heterologous cytoplasm were much poorer than those of homologous recipients, and most of the former died by 1 week after operation. It is postulated that amoebae are capable of recognizing heteiologous organelles introduced into the cytoplasm and that they respond by expulsion and/or destruction of the foreign cellular components. The previously described lethal effect of heterologous cytoplasm was confirmed.
Isolation and characterization of membranes from the cells of maize root tips
Authors: Baydoun Elias A-H. , Northcote D. H.
Published: April 2021

A discontinuous sucrose density gradient was used to separate membrane fractions from a homogenate of maize rcottips. Endoplasmic reticulum-, Golgi apparatus-, plasma membrane- and mitochondria-rich fractions were identified by their enzymic characteristics and by their appearance under the electron microscope. Maize roots were incubated in vivo with D-[U-14C]glucose, [Me-14C]choline chloride and diazotized [U-3H]sulphanilic acid. The pattern of incorporation of radioactivity into the various membrane fractions was investigated. Analyses of the polypeptide chains of the membrane fractions by SDS-polyacrylamide gel electrophoresis showed that the mitochondria-rich fraction had a different pattern of polypeptides from that of the other membrane fractions. The results are discussed in relation to the hypotheses of endomembrane flow and differentiation.
On the role of small peptides in the regulation of rna synthesis in Tetrahymena pyriformis
Authors: Andersen H. A. , Lykkesfeldt Anne E. , Nielsen S.J.
Published: April 2021

Tetrahymena cells secrete a factor which inhibits RNA synthesis in vivo and in vitro. The factor is a relatively small peptide with a molecular weight between 300 and 1500 Daltons. Other, non-specific peptides in the broth medium or added to a chemically defined medium have a stimulatory effect on RNA synthesis in vivo and such peptides also stimulate the in vitro synthesis of RNA in an r-chromatin preparation. On the basis of these results we conclude that such extracellular small peptides compete with a specific factor which is part of the intracellular regulatory mechanism controlling the rate of RNA synthesis. The consequence of such competition is a high overproduction of ribosomal RNA in cells inoculated on peptide-rich broth media.
Effects of Colchicine on the Golgi Complex and Gerl of Cultured Rat Peritoneal Macrophages and Epiphyseal Chondrocytes
Authors: THYBERG JOHAN , PIASEK ANDRZEJ , MOSKALEWSKI STANISLAW
Published: April 2021

Thioglycollate-elicited rat peritoneal macrophages and epiphyseal chondrocytes were cultured in vitro, treated with colchicine, and then studied by electron-microscopic and cytochemical techniques. Colchicine, but not lumicolchicine, caused disappearance of cytoplasmic microtubules and breakup of the Golgi complex with spreading of its dictyosomes from a well defined juxta nuclear area throughout the cytoplasm. There was also an altered distribution of lysosomes, which oriented themselves close to the dictyosomes both in controland colchicine-treated cells. Further, the structure of the individual dictyosomes was changed, especially in the chondrocytes. GERL equivalents were observed in control cells but were difficult to detect after exposure to colchicine. Reaction product for thiamine pyrophosphatase was found in narrow cisternae on the inner side of the dictyosomes in control cells but invacuole-like structures in colchicine-treated cells. Reaction product for acid phosphatase was present in GERL equivalents and lysosomes in control cells but mainly in lysosomes incolchicine-treated cells. Nevertheless, the total specific activities of these enzymes as well as of 5â€²-nucleotidase, a plasma membrane marker, remained unaffected by the drug treatment.

These observations show that cytoplasmic microtubules play an important and, in many respects similar, cytoskeletal role in two so functionally diverse cell types as macrophages and chondrocytes. They are particularly important for the structural integrity of the Golgi complex, which in both cells is normally organized in the area around the centrioles, from which numerous microtubules radiate into the cytoplasm. The observations further suggest that GERL is an integrated part of the Golgi complex in these cells.
Effects of colchicine on endocytosis of horseradish peroxidase by rat peritoneal macrophages
Authors: Piasek Andrzej , Thyberg Johan
Published: April 2021

Horseradish peroxidase (HRP) was used as an exogenous marker to study the effects of microtubule-disruptive drugs on endocytosis in cultures of thioglycollate-elicited rat peritoneal macrophages. Colchicine and vinblastine, but not lumicolchicine or cytochalasin B, reduced HRP uptake by about 30–40 %. However, as determined by stereological measurements, the size of the HRP-containing compartment within the cells remained unaltered. In both control cells and cells treated with colchicine or vinblastine the HRP-reactive vesicles were preferentially located close to the dictyosomes (stacks of cistemae) despite the fact that the Golgi complex was disorganized in the treated cells. These results suggest that intact cytoplasmic microtubules are required to maintain a normal rate of fluid phase endocytosis in macrophages. On the other hand, it seems as if microtubules are not necessary for the translocation of newly formed endocytic vesicles/lysosomes to the dictyosomes, from which they probably are supplied with digestive enzymes.
Adhesion of leukocytes to endothelium: Roles of divalent cations, surface charge, chemotactic agents and substrate
Authors: Hoover R. L. , Folger R. , Haering W. A. , Ware B. R. , Karnovsky M. J.
Published: April 2021

The attachment of polymorphonuclear leukocytes (PMN) to the endothelial lining of blood vessels is an important initial event in the acute inflammatory reaction. Experiments were carried out to examine some of the parameters of this adhesive interaction and the extent to which the substrate (endothelium) plays a role in controlling the process. Using a monolayer collection assay for adhesion, we found a requirement for divalent cations. Mn’+produces maximal adhesion followed by Zn2+ > Ni2+ > Mg2+ > Ba2+ > Ca2+. Pretreatment of either the endothelium or PMN with chemotactic agents (zymosan-activated serum, a bacterial filtrate, Csa and formyl-methionyl-leucyl-phenylalanine) causes an increase in the attachment of PMN to endothelial monolayers. Modulations of net surface charge, as measured by laser Doppler electrophoresis, are not correlated to alterations in adhesion. Mn 2+, which produces maximal adhesion, reduces the net surface charge to the same extent as Ca2+, which has the smallest effect on adhesion. Similarly, reductions in net surface charge are not responsible for the increases in adhesion due to the chemotactic agents because there are no differences in electrophoretic mobilities between cells treated with either chemotactic agents or their appropriate controls. Scatchard analysis of the binding of the chemotactic tripeptide, formyl-methionyl-leucyl-phenylalanine, indicates the presence of high-affinity binding sites on the surface of the endothelium. The results suggest a role for the endothelium in mediating the adhesive interaction with the PMN.
Fine structure and behaviour of a pericentric inversion in the sand rat, Psammomys obesus
Authors: Ashley Terry , Moses M. J. , Solari A. J.
Published: April 2021

In pachytene spermatocytes of the sand rat, Psammomys obesus, a long autosomal bivalent was observed, which was asynaptic for a large interstitial segment of its length in early pachytene. This bivalent also exhibited unaligned kinetochores. In late pachytene spermatocytes all autosomal bivalents were fully synapsed, but one of the shortest bivalents now possessed unaligned kinetochores. Evidence is presented in support of the proposition that the asynaptic interstitial region observed in early pachytene is due to the bivalent being heterozygous for a pericentric inversion. Using the maximum extent of homologous pairing, the break points were mapped at 26% from one end and 20% from the other. The unaligned kinetochores support the proposal that the aberration is an inversion and measurements of their positions confirm the estimated break points. In one cell a bivalent with interstitial (but no terminal) synapsis also confirms the inversion hypothesis. It is proposed that the bivalent is so small that topological considerations prevent the formation of the expected inversion loop. Evidence is also presented that complete synapsis of the bivalent during late pachytene can be attributed to ‘synaptic adjustment’, characterized by non-homologous synapsis (heterosynapsis). The position of the aberrant bivalent in relation to the sex chromosomes also changes during pachytene. When the bivalent is incompletely synapsed it generally associates by its ends with the ends of the sex chromosomes, but when it is non-homologously synapsed it is not associated with them.
Intracellular transport and secretion of fibroin in the posterior silk gland of the silkworm Bombyx mori
Authors: Sasaki Sadao , Nakajima Etsuko , Fujii-Kuriyama Yoshiaki , Tashiro Yutaka
Published: April 2021

Intracellular transport and secretion of fibroin in the posterior silk gland cells of the silkworm, Bombyx mori, were investigated in relation to the radial microtubule and circular microtubule-microfilament systems of the cells.

The silk glands were pulse-labelled for 3 min with [3H]glycine in vitro and then chased in media containing excess cold glycine and in some cases antimitotic reagents (colchicine or vinblastine) or cytochalasin (B or D), and the flow of the label in the glands was investigated by radioautography. It was revealed that the label initially located over the rough endoplasmic reticulum subsequently moves to the Golgi bodies to be condensed there. The secretory granules of fibroin or fibroin globules thus formed are transported via the radial microtubule system to the apical cytoplasm to be secreted there under some regulation by the circular microtubule-microfilament system. In the presence of colchicine or vinblastine, the secretion of fibroin was suppressed and marked accumulation of fibroin globules in the Golgi regions was observed, while in the presence of cytochalasin B or D the secretion was accelerated and extensive invagination of the luminal surface, which was probably due to the serial exocytosis of fibroin globules, was observed. These results suggest that the radial microtubule system and the circular microtubule-microfilament system are responsible for intracellular transport of fibroin globules from Golgi bodies to the apical cytoplasm and secretion by exocytosis at the luminal surface, respectively.
Fibonectin is a component of the surface coat of human neutrophils
Authors: Hoffstein S. T. , Weissmann G. , Pearlstein E.
Published: April 2021

Although adherence to surfaces is central to neutrophil function many of the determinants of neutrophil adherence are still unknown. The possible involvement of cell surface material, fibronectin in particular, was therefore studied. Surface coat material was visualized ultra-structurally by the ferrocyanide-reduced osmium technique of Kamovsky (1971). Loosely attached surface coat material was seen distributed uniformly on cells in suspension. Indirect immunofluorescence indicated the presence of fibronectin on the neutrophil surface. Distribution of fibronectin as determined by indirect immunoferritin localization corresponded with the distribution of cell coat material. Some, if not all, of this fibronectin was synthesized by neutrophils themselves since metabolically labelled fibronectin could be obtained by immunoprecipitation after short-term culture with [35S]methionine. Neutrophils also adhere to Sepharose beads to which gelatin is covalently linked (GS) but not to plain Sepharose beads (PS). In the process they transfer surface coat material to GS but not PS. Similar transfer was seen when cells were permitted to adhere to glass or plastic coverslips. Indirect immunofluorescence showed that fibronectin-containing material was transferred from neutrophils to GS but not PS. Parallel studies with antisera to 2 other plasma proteins, factor VIIIR and alpha1-antitrypsin showed that neutrophils did not transfer these to either GS or PS beads. The data suggest that material antigenically and functionally related to fibronectin is associated with the extracellular coat of neutrophils and is transferred with cell surface material to surfaces to which neutrophils adhere.
Differentiation between mitochondrial and cytoplasmic protein subunits of blowfly flight muscle mitochondria synthesized in vivo
Authors: Ashour M. Badr , Tribe Michael
Published: April 2021

Total adult blowfly flight-muscle mitochondrial protein was labelled in vivo with [14C]leucine. The labelled proteins were enumerated and characterized by their electrophoretic mobility using sodium dodecyl sulphate/polyacrylamide gel electrophoresis and autoradiography.

When different gel concentrations were used to resolve the maximum number of bands and their molecular weights, it was possible to observe at least 35 electrophoretic bands after staining and scanning; their molecular weights ranged between 11000 and 130000.

When mitochondria were labelled in the presence of cycloheximide, only 6–8 bands could be identified on gradient gels after electrophoresis and autoradiography. By comparison, controls (where cycloheximide was absent), which were run alongside the drug-treated mitochondria, revealed 17–20 radioactively labelled bands from densitométrie tracings. Whilst the molecular weights of these bands could be estimated, it was difficult to identify the precise nature and function of the proteins made in these mitochondria.
Motility of basal fragments of sea urchin sperm flagella
Authors: Goldstein Stuart F.
Published: April 2021

Both live and reactivated sea urchin sperm flagella were broken by passage through a pipette. Distal fragments stopped, but basal fragments continued to beat. Intact flagella were about 48 /4m long; basal fragments were about 4–20 μm long.

Beat periods of tritonated fragments were 1 1% shorter than those of unbroken controls, possibly reflecting decreased viscous loading; beat periods of live fragments were 18% shorter than those of unbroken controls, possibly reflecting reduced rates of ATP consumption as well as decreased viscous loading.

The undulations of basal fragments were compared with those of the basal regions of unbroken flagella, using the patterns of development of the radii and angles of basal bends. Fragments closely resembled basal regions of unbroken flagella, except that bends tended to open as they approached the distal end of a fragment, so that their radii increased more rapidly than those of unbroken flagella.

Fragments about 4 μm long contained only one bend during part of the cycle, and appeared to be straight during part of the cycle. They flipped back and forth with fairly constant angular speeds and abrupt changes in direction, so that plots of angle between their distal end and base often resembled triangular waves, although the peaks of the waveforms were often rounded. This behaviour suggests a mechanism in which sliding switches between 2 modes. Both the speed of sliding and the maximum angles attained in one direction of bending were greater than those attained in the other direction, suggesting differences between the doublets on the 2 sides of the axoneme. Sliding of the doublets continued at fast speeds as the fragments straightened, in contrast to the characteristics of some curvature-sensitive models.

These flagellar fragments provide a simplified system for the study of flagellar oscillations.
Cell adhesion on model substrata: Threshold effects and receptor modulation
Authors: Aplin J. D. , Hughes R. C.
Published: April 2021

Trypsinized BHK cells become attached to glass that has been derivatized with a variety of lectins with well-defined specificity for cell-surface carbohydrates. Provided a threshold concentration of glass-immobilized protein is present the cells undergo a transformation to a wellspread morphology. The matrix density of lectins (ricin and concanavalin A) required to trigger this morphological transformation is higher by 10 to 40-fold than the value determined earlier (Hughes, Pena, Clark & Dourmashkin, 1979) for fibronectin.

Cells resistant to the toxic lectin, ricin, and expressing 10% or less of ricin-binding carbohydrate groups at their cell surfaces require correspondingly greater matrix densities of ricin to promote active cell spreading. All cell lines spread equally well on concanavalin A-based matrices consistent with their similar binding properties.

The quantitative interaction of complementary molecules on the cell surface and matrix, promoting cell adhesion, is demonstrated by these results and a model is proposed for the events leading to a well-spread cell morphology on a protein-coated substratum.
Oxygen gradients cause pattern orientation in Dictyostelium cell clumps
Authors: Sternfeld John , David Charles N.
Published: April 2021

We have investigated the formation of the prestalk-prespore pattern in Dictyostelium discoideum. Pattern formation occurs in clumps of Dictyostelium cells embedded in agar under a 100% oxygen atmosphere. Agar embedding allows us to control spatially the environment surrounding the cell clumps. Our results suggest that the ambient oxygen concentration plays a role in controlling the size of the multicellular mass. Further, oxygen gradients established across clumps embedded in agar or held in holes in a plastic barrier cause orientation of the prestalk-prespore pattern such that the anterior prestalk region forms at the highest end of the gradient. The results also indicate that developing cells have the ability to migrate up a gradient of oxygen.
Freeze-fracture analysis of membrane events during early neogenesis of cilia in Tetrahymena: changes in fairy-ring morphology and membrane topography
Authors: Hufnagel Linda A.
Published: April 2021

A freeze-fracture analysis of early neogenesis of somatic and oral cilia of Tetrahymena was conducted using exponentially grown cultures and also cells induced to undergo oral reorganization. In this report, presumptive ciliary domains (PCDs), sites of future outgrowth of somatic cilia, are identified and their membrane structure is described in detail. The fairy ring, an array of membrane particles that occurs within the PCD and appears to be a precursor of the ciliary necklace, is described. A sequence of early stages in the formation of the ciliary necklace of somatic cilia is deduced from topographical information and membrane particle arrangements and numbers. Evidence is presented that basal bodies are seated at the cell surface prior to initiation of necklace assembly and a possible role for the basal body in necklace assembly is suggested. In dividing cells, new oral cilia grow out prior to orientation of cilia-parasomal sac complexes relative to cell axes. In dividing cells and during oral reorganization, new cilia also develop prior to their alignment into membranelles. Thus, growth of cilia is independent of their spatial orientation. Fairy’ rings were not observed during oral reorganization. During cell division, proliferation of new cilia is accompanied by the formation of a network of junctions between a cortical system of membranous cisternae, the cortical ‘alveoli’. These interalveolar junctions may serve as tracks for early positioning and orientation of new oral basal bodies.