bluuebunny/crossref_metadata_2025 huggingface dataset:
Adhesion and locomotion of granulocytes under flow conditions
Authors: Doroszewski Jan , Kiwala Anna
Published: April 2021

The aim of this study was to compare the strength of the surface adhesion of migrating human granulocytes and the main parameters of their locomotion under the influence of various external forces. The strength of adhesion of granulocytes moving in a quiescent medium was studied by detaching them gravitationally from the plane surface situated above them. In these conditions the force of adhesion is of the same order of magnitude as the gravitational force operating upon the cells. The locomotion characteristics of granulocytes migrating on a surface below them are similar to those observed during their movement on a surface above. When the granulocytes migrate with the medium flowing past them, they are not detached from the surface even by relatively great shearing forces (10 and 100 times greater in comparison with the gravitational force) and the locomotion parameters are only slightly modified. The results show that granulocytes are able to migrate in a similar manner when they are subjected to various external forces.
The effects of glycosylation inhibitors on the proliferation of a spontaneously transformed cell line (3T6) in vitro
Authors: Engstrom Wilhelm , Larsson Olle
Published: April 2021

We have examined the effects of different inhibitors of glycosylation processing on the proliferation of a spontaneously transformed murine cell line (3T6) in vitro. It was found that whereas two compounds that specifically inhibit distal steps in the glycosylation chain (swainsonine and castanospermine) only exerted marginal inhibitory effects on cell multiplication, a proximal inhibitor (tunicamycin) efficiently decreased the rate of DNA synthesis in a dose-dependent fashion. This tunicamycin-induced inhibitory effect on cell proliferation was cell cycle-specific, in the sense that cells in G1 only were blocked in their cell cycle progression. Like others (Volpe & Goldberg, 1983), we found that tunicamycin inhibited the activity of 3-hydroxy-3-methylglutaryl coenzyme-A reductase (HMG-CoA), which constitutes the ratelimiting step in the biosynthesis of cholesterol and isoprenoid derivatives, by cata lysing the reduction of HMG-CoA to mevalonate, and it has been suggested that it plays a role in the control of cell proliferation and in tumour transformation. This raises the question as to whether tunicamycin exerts its inhibitory effects on cell proliferation via the isprene-synthetic pathway in addition to its effects on aspargine-linked glycosylation. By adding exogenous mevalonate, the rate-limiting step at which HMG-CoA reductase converts HMG-CoA to mevalonate can be bypassed. We found that addition of mevalonate partially reverses the effects of tunicamycin on cell proliferation. This suggests that tunicamycin exerts different effects, which taken together lead to a cessation of cell proliferation. One of these effects is likely to be mediated via the mevalonate-synthetic pathway.
Characterization of D-[3H]cis-diltiazem binding to membrane fractions and specific binding of calcium channel blockers to isolated flagellar membranes of Chlamydomonas reinhardtii
Authors: Dolle R. , Nultsch W.
Published: April 2021

Plasma membranes were separated from the intracellular membranes by using an aqueous two-polymer phase system. D-[3H]cis-diltiazem was employed to characterize benzothiazepine-selective receptors in these different membrane fractions of Chlamydomonas reinhardtii. The separation revealed that one type of binding site with higher affinity (KD = 33 nM) can be attributed to the intracellular membrane fraction and a second type with lower affinity (KD = 313nM) to the plasma membrane fraction. The apparent dissociation constants determined from the association and dissociation rate constants in kinetic experiments are comparable to those determined by saturation experiments. The maximum numbers of binding sites of the intracellular mem-brane fraction and the plasma membrane fraction are Bmax = 6·4pmolmg-1 protein and Bmax= 19pmolmg-1 protein, respectively. D-[3H]cis-diltiazem binding is inhibited by (±)ver-apamil and calcium chloride in both fractions. Moreover, nifedipine stimulates D-[3H]cis-diltia-zem binding by the intracellular membrane fraction, but shows no effect on the plasma membrane fraction.

Ligand displacement binding studies with isolated flagella revealed the occurrence of a D-cis- diltiazem binding site with about the same affinity to this drug (KD = 400 nM) as the one found in the plasma membrane fraction. The maximum number of binding sites is 4-5pmolmg-1 protein. The apparent dissociation constants for specific [3H]nimodipine and [3H]verapamil binding to the flagella were calculated to be 8nM and 38 nM, respectively. The corresponding Bmax values are 345fmolmg-1 protein and 1’Spmolmg-1 protein, respectively.
Metaphase position of an interchange quadrivalent of Allium triquetrum III. the expected distribution based on randomness
Authors: Rickards Geoffrey K. , Baker Wendy A.
Published: April 2021

The position of an interchange quadrivalent at metaphase I of Allium triquetrum was modelled so as to simulate the original placement of the quadrivalent in the spindle and the preparation of linear spreads through squashing. In this way an expected distribution for the quadrivalent in linear spreads was generated. The procedure used polar views of metaphase I to which the quadrivalent was assigned pairs of positions normally occupied by bivalents. The positions of the bivalents and assigned quadrivalent were then projected into a linear array and analysed as ‘real’ data. Comparisons with observed distributions showed that a general bias in favour of marginal placement of the quadrivalent in the linear array is expected; and also showed that the quadrivalent is positioned non-randomly in the metaphase plate prior to slide preparation.
Phagosome formation in Paramecium:, Effects of solid particles
Authors: Fok Agnes K. , Sison Benjamin C. , Ueno Marilynn S. , Allen Richard D.
Published: April 2021

Digestive vacuole (DV) formation in Paramecium can be separated into four steps: sequestration and recycling of the spent DV membrane, sweeping and concentrating of particles into the nascent DV, vacuole growth, and the release of the nascent DV. How the size, load and surface charge of solid particles affected formation and subsequently the digestive processes in log-phase cells were investigated. Pulsing cells continuously with beads resulted in an initial linear increase, followed by a steady state, of labelled DVs. Above a certain threshold concentration, the rate of formation and the size of the DVs formed (as well as the steady state) all increased with increasing bead load, so that for a 16-fold increase in bead load, a corresponding fourfold increase in the incorporation of the recycled membrane into the DVs was observed. The threshold values, which depended on the sensitivity of the technique used to score these DVs, were lowered as bead size increased. The steady state of labelled DVs was shown to correspond to a strict balance between the formation and defecation rates as shown by efflux measurements and pulse-chase protocols using two consecutive labels. The duration of the pulse required to reach these steady states was inversely proportional to the logarithm of the bead number at low bead loads but remained constant at higher bead loads. The formation rates and the DV size were similar when cells were pulsed with beads from 0·5 to 3 μm, but DV size increased using beads of 4·5 and 5·7 μm. The maximal bead size that could be ingested was − 10 μm. Beads with a positive surface charge reduced the formation rate as well as the DV size. These results show that: (1) under normal conditions particle concentration can determine the formation rate and the DV size; (2) paramecia can form DVs continuously without any detectable interruptions; and (3) the rate of defecation and thus the rate of recycling of spent DV membrane is dependent on the rate of DV formation.
Presence And Distribution Of Specific Prosome Antigens Change As A Function Of Embryonic Development And Tissue-Type Differentiation In Pleurodeles Waltl
Authors: Pal J. K. , Gounon P. , Grossi de SA M.-F. , Scherrer K.
Published: April 2021

The prosomes, biochemically well characterized small RNA-protein complexes, found associated with mRNA in all eukaryotic cells tested, have been identified as maternal components in sea urchin and chick embryos. In this study, we investigated their presence and cytolocalization in the oocytes and embryos of Pleurodeles waltl by immunoblot analysis and immunofluorescence, using monoclonal antibodies prepared against duck prosome proteins. Of the four anti-bodies tested, three recognized the corresponding antigens in oocyte total protein extracts. Immuno-fluorescence analysis, using the three prosomal antibodies, demonstrated a drastic change in the localization of the prosome antigens, which changed from the cytoplasm to the nucleus during oogenesis. In the nucleus, in diplotene stages, prosomal antigens appeared to be associated with the lampbrush chromosomes and the nuclear matrix.

During embryogenesis, the subcellular distribution of the prosome antigens was a function of development and differentiation: in the cleavage stages up to the mid-blastula they were localized in the cytoplasm and on the plasma membrane, while in the late blastula, gastrula and neurula they were in the nucleus. Interestingly, one of the prosome antigens, p31K, was found to be in a different location in certain cells in the animal pole of the mid-blastula and was absent in the neural tissue in the neurula. In still later stages, in the free-swimming larva, all three antigens were localized in the cytoplasm, specifically in certain cell types in the epidermal tissues. Furthermore, they were sectorially distributed in the cytoplasm. These data taken together indicate the possible presence of tissue-type-specific prosome antigens in Pleurodeles. Differentiation-dependent subcellular localization of the prosome antigens suggests a cell-compartment-related multiple function of prosomes.
Variation In Thin Filament Size In The Skeletal Muscle Of The Frog
Authors: Corsi Andrea , Granata Anna Luisa , Vecchi Cesare , Strabbioli Rosanna , Re Lamberto
Published: April 2021

The sartorius muscle of Rana esculenta was fixed and dehydrated by different methods and cross-sections of sarcomeres of different lengths were examined by electron microscopy. The area within the outlines of the thin filaments in negatives was measured using a high-resolution television system and a graphics tablet or by using a microdensitometer and computer processing the images with a density threshold above the background level.

In all specimens the area of the thin filaments in the I-bands was found to be larger than in the fizones of the A-bands where the thick and thin filaments interpenetrate. The difference was statistically significant and independent of the length of the sarcomere. The results are in agreement with previous observations in glycerol-extracted fibres. It is suggested that the change in size of the thin filaments might be accounted for by some interaction with the thick filaments.
The 3T3 cell cycle at low proliferation rates
Authors: Brooks Robert F. , Riddle Peter N.
Published: April 2021

When the proliferation rate of Swiss 3T3 cells is decreased by limiting the availability of growth factors, cell cycle variability increases, as predicted by the transition probability model. Nevertheless, the transition probabilities would appear to play a relatively minor role in the regulation of proliferation rate. Instead, at least 40% of the increase in the average cycle time is brought about by an elongation of the minimum cycle time (i.e. the ‘deterministic’ part of the cycle). In addition, we have found that a substantial proportion of the cells (roughly 20%, in the present experiments, for doubling times of the order of 35–40 h) drop out of cycle in each generation, leading to a growth fraction of less than 1·0. The non-dividing cells, which we have previously shown to remain capable of division, would seem to support the existence of a Go state outside the normal cell cycle, and distinct from the indeter-minate states postulated by the transition probability model. Because of the generation of non-dividing cells at low proliferation rates, the log α and β plots (distributions of cycle times, and sibling cycle time differences, respectively) are markedly concave, with a continuously decreasing slope. The transition probabilities cannot therefore be estimated directly and it is impossible to determine the extent to which they contribute to the regulation of proliferation rate. Rather, our data suggest that the transition probabilities are not uniform throughout the population under these conditions, but vary substantially from cell to cell.

In addition to the changes in cell cycle kinetics, we also report an increased failure rate of cyto-kinesis, at low proliferation rates, leading initially to the appearance of binucleate cells. Such failures of cytokinesis may be responsible for the well-known rise in the incidence of binucleate and polyploid cells in the liver, with age.
In Situ Preparation Of The Nuclear Matrix Of Physarum Polycephalum: Ultrastructural And Biochemical Analysis Of Different Matrix Isolation Procedures
Authors: Waitz Werner , Loidl Peter
Published: April 2021

A novel method for in situ preparation of nuclear matrix from whole plasmodia of Physarum polycephalum without isolation of nuclei is presented. Plasmodia are encapsulated in agarose beads and after solubilization of the cytoplasm the nuclear matrix is prepared. With this quick and easy technique nuclear matrix can be reproducibly prepared with perfect recovery. We compared the ultrastructural and biochemical properties of the matrix after three different matrix isolation procedures: preparation with high salt, ammonium sulphate and lithium diiodosalicylic acid. The results show that the ultrastructure and protein composition of the three types of matrix are very similar or even identical. We conclude that many of the conflicting results on nuclear matrix in the literature are due to perturbations of nuclear integrity during the isolation of nuclei. For this reason the new in situ method is an important approach in the standardization of nuclear matrix isolation.
Expression of a mutated ras gene in Dictyostelium discoideum alters the binding of cyclic AMP to its chemotactic receptor
Authors: Ludérus M. E. E. , Reymond C. D. , Van Haastert P. J. M. , Van Driel R.
Published: April 2021

Dictyostelium discoideum cells contain a ras gene that codes for a polypeptide that is highly homologous to the human ras proteins. Extra copies of the wild-type gene or a gene carrying a missense mutation in codon 12 (ras-Glyl2 and ras-Thrl2, respectively) have been introduced into Dictyo-stelium cells by transformation.

We have investigated the properties of the chemotactic cell surface cyclic AMP receptor in crude membrane preparations of wild-type Dictyostelium cells and ras-Glyl2 and ras-Thrl2 transformants. In vitro, an ATP- and Ca2+-dependent reduction of the number of cyclic AMP receptors was observed in membranes from all three cell types. The number of available receptors was decreased maximally by about 50%. In the presence of ATP the half-maximal Ca2+ concentration required for this process was about 10−5M in wild-type and ras-Glyl2 membranes, and less than 10−7M in ras-Thrl2 membranes. Addition of GTP (but not GDP) or the phorbol ester PMA (phorbol-12-myristate-13-acetate) reduced the Ca2+ requirement of the process in wild-type and ras-Gly12 membranes to the physiological level of less than 10−7M. In membranes derived from ras-Thrl2 cells addition of GTP or PMA had no effect.

The results indicate that D. discoideum cells contain a cyclic AMP receptor-controlling pathway that can be activated in vitro and involves a GTP-binding protein and a Ca2+ plus ATP-dependent activity, possibly protein kinase C. It is concluded that the ras protein specifically inter-acts with this pathway; the pathway appears to be constitutively activated by the mutated ras gene product.
Cytotoxic effects of cisplatin, cis-dichlorodiammineplatinum(ll), on Tetrahymena
Authors: Nilsson Jytte R.
Published: April 2021

A study was made of the effects of cisplatin, cis- dichlorodiammineplatinum(II) (5-250 mg 1−1), on the physiology and fine structure of Tetrahymena. The physiological effects observed were dose-dependent. Endocytosis was inhibited reversibly in all, but late in the high, concentrations. After an initial dose-related increase, due to division of cells most advanced in the cell cycle, proliferation ceased for at least two normal cell generations (6h) in 50 and 100 mg drug 1− 1, but for 24h in 250mgl−1, after which multiplication was resumed in a dose-dependent manner. Exposure to cisplatin resulted in the appearance of small, refractive granules and platinum (i.e. electron-dense material) accumulated in these granules. Fine structural observations of cells exposed to 250 mg drug I− 1 showed nucleolar fusion and appearance initially of lipid droplets, dense granules and autophagosomes. A time-dependent redistribution of cell organelles was revealed by morphometry; in particular, the mitochondria increased in number, but decreased in size. Moreover, after prolonged treatment (24 h) and without cell division, the inner mitochondrial membrane had diminished and the ratio of the inner to the outer mitochondrial membrane was only half of the value for control mitochondria. Concomitantly with this decrease, the cell content of ATP was reduced to a similar extent. The findings indicate a specific action of cisplatin on mitochondria, resembling that induced in Tetrahymena by chloramphenicol and methotrexate.
Molecular organization of cell-wall crystals from Chlamydomonas reinhardtii and Volvox carteri
Authors: Goodenough Ursula W. , Heuser John E.
Published: April 2021

The extracellular matrices of Chlamydomonas reinhardtii and Volvox carteri contain homologous salt-extractable crystalline layers that will self-assemble in vitro. The organization of these crystals is examined using the quick-freeze deep-etch technique. In C. reinhardtii, the outer layer of the crystal is an open polygonal weave (W6B); this is shown to be constructed from regular overlapping associations between the fibrous hydroxyproline-rich glycoprotein GP1. The inner layer of the crystal (W6A) is shown to be a copolymer of GP2 and GP3. The bulky globular domains of these glycoproteins form the rows of granules seen on the upper and lower surfaces of W6A in both Chlamydomonas and Volvox, and their filamentous domains interact to form a dense meshwork.
The shape of cultured epithelial cells does not depend on the integrity of their microtubules
Authors: Middleton C. A. , Brown A. F. , Brown R. M. , Roberts D. J. H.
Published: April 2021

Fibroblasts are thought to require an intact system of cytoplasmic microtubules in order both to adopt and to maintain a polarized morphology in culture, but whether the same is true for epithelial cells is not clear. We therefore compared the effects of the microtubule-disrupting drugs, colcemid and nocodazole, on the morphology of isolated embryonic chick heart fibroblasts (HF), corneal epithelial (CE) and epidermal epithelial (EE) cells. Immunofluorescence observations showed that all three cell types contained abundant microtubules when cultured in control medium and that these were absent from cells cultured in medium containing either colcemid or nocodazole. Qualitative observations suggested that these drugs inhibited the polarization of spreading HF but had no effect on the morphology of either of the epithelial cell types. We confirmed this observation quantitatively using two measures of cell shape, elongation and dispersion, both of which increase with increasing polarization. Our measurements show that microtubuledisrupting drugs significantly reduce both the elongation and dispersion of spreading HF but do not have a significant effect on either of these measures for the epithelial cell types.

We quantified in a similar way the effects of microtubule-disrupting drugs on the morphology of all three cell types that had previously spread in control medium. We found that transferring spread HF to colcemid-containing medium significantly reduced both the elongation and dispersion of these cells but that the same treatment had no effect on these measures for either of the epithelial cell types.

Our observations suggest that, unlike the fibroblasts, the epithelial cell types we have studied do not require microtubules either to adopt or to maintain a polarized morphology.
Mechanism of ca2+ inhibition of cytoplasmic streaming in lily pollen tubes
Authors: Kohno Tadashi , Shimmen Teruo
Published: April 2021

Using a Ca2+ ionophore, A23187, the free Ca2+ concentration ([Ca2+]) in the cytoplasm of pollen tubes of Liliutn longiflorum was controlled from the cell exterior. At [Ca2+] higher than 1·0×10−5M (pCa5-0), cytoplasmic streaming was inhibited, and the inhibition was irreversible. The ATP content did not change, but actin filaments were fragmented and formed aggregates. A subsequent decrease in [Ca2+] almost stopped the progress of the actin filament fragmentation, but filamentous actin did not re-form from the fragmented actin. In a previous paper, we reported that pollen tube organelle movement along characean actin bundles was inhibited by Ca2+ at 10−sM levels and the inhibition was reversible. In the present study, the reversibility was also demonstrated using an in situ Ca2+ treatment. Organelles were isolated from pollen tubes that had been treated with high [Ca2+] and A23187. They moved along characean actin bundles in Ca2+-free medium.

It is concluded that Ca2+ inhibition of cytoplasmic streaming can be attributed to both inactivation of myosin and fragmentation of actin. The irreversibility of Ca2+ inhibition in situ is attributed to the irreversible fragmentation of actin filaments.
Chemical signal-response in diatoms of the genus Amphora
Authors: Cooksey Barbara , Cooksey Keith E.
Published: April 2021

The marine diatom Ampbora coffeaeformis is positively chemotactic to glucose and sugars of similar structure. A free hydroxyl group is required at the 2-position of the ring; however, D-mannose (a toxic sugar) and L-glucose promote negative chemotaxis. Sugar metabolism is not necessary for a chemosen-sory response. When the direction of higher concentration in a D-glucose gradient is reversed, cells already orientated reverse their direction of movement. Pretreatment of diatoms with a uniform concentration of D-glucose before exposure to a concentration gradient eliminates the chemotactic response. When diatom cells attached to surfaces in the presence of 5 mM-Ca2+ are exposed to 0·25–0,625mM Ca2+, their motility drops rapidly. However, when this experiment is carried out in the presence of a uniform concentration of D-glucose or 3-O-methyl-D-glucose, motility is sustained for 25–30 min before falling. Speed of motility is also increased during this period. These results can be interpreted in terms of an agonist bindingsecretion coupling model for diatom chemotaxis.
Localization of calmodulin in the enterocyte of Necturus small intestine
Authors: Scully R. R. , Dedman J. R. , Schultz S. G.
Published: April 2021

Calmodulin was localized in the small intestine of Necturus maculosa at both the light- and electron-microscopic levels utilizing an affinity-purified, monospecific antibody and immunoperoxidase cytochemistry. The microvilli and basolateral membranes of the epithelium were highly reactive, the cytoplasm was moderately reactive. Connective tissue, endothelia, and muscularis of the submucosa were also reactive. The mitochondrial matrix, nuclear envelope, and terminal web, and mucous granules of goblet cells were unreactive. Omission of the primary antibody, substitution of immunoglobulin not bound to the affinity column or inappropriate immunoglobulin (sheep anti-viral src product) for the primary antibody, caused no immunoreaction product to be formed.
Maintenance of multiplication rate stability by cell populations in the face of heterogeneity among individual cells
Authors: Grundel Ralph , Rubin Harry
Published: April 2021

We addressed the question of how a population of cells can maintain a constant multiplication rate given the heterogeneity of its individual members. Using the NIH 3T3 line of mouse embryo cells, comparisons were made of multiplication rates between offspring subclones and the parental clones from which the subclones were derived. Parents at all levels of multiplication rate produced offspring with a wide range of multiplication rates. Offspring from parent cells with the highest growth rates rarely exceeded their parents in rate of multiplication. Offspring from slow-growing parents, however, often exceeded the parents.

It is concluded that the multiplication of NIH 3T3 populations represents constant diversification in multiplication rate: heterogeneous parents producing heterogeneous offspring. Population growth rates can remain stable because the fastest-growing parents generally produce offspring that multiply slower than the parents while the slowest parents often produce offspring that multiply faster than the parents.
Supramolecular structure of the thylakoid membrane of Prochlorothrix hollandica: A chlorophyll b-containing prokaryote
Authors: Miller Kenneth R. , Jacob Jules S. , Burger-Wiersma Tineke , Matthij Hans C. P.
Published: April 2021

Prochlorothrix hollandica is a newly described photosynthetic prokaryote, which contains chlorophylls a and b. In this paper we report the results of freeze fracture and freeze etch studies of the organization of the photosynthetic thylakoid membranes of Prochlorothrix. These membranes exhibit four distinct fracture faces in freeze fractured preparations, two of which are derived from membrane splitting in stacked regions of the thylakoid membrane, and two of which are derived from nonstacked regions. The existence of these four faces confirms that the thylakoid membranes of Prochlorothrix, like those of green plants, display true membrane stacking and have different internal composition in stacked and non-stacked regions, a phenomenon that has been given the name lateral heterogeneity. The general details of these fracture faces are similar to those of green plants, although the intramembrane particles of Prochlorothrix are generally smaller than those of green plants by as much as 30%.

Freeze etched membrane surfaces have also been studied, and the results of these studies confirm freeze fracture observations. The outer surface of the thylakoid membrane displays both small (less than 8·0 nm) and large (greater than 10·0 nm) particles. The inner surface of the thylakoid membrane is covered with tetrameric particles, which are concentrated into stacked membrane regions, a situation that is similar to the inner surfaces of the thylakoid membranes of green plants. These tetramers have never before been reported in a prokaryote. The photosynthetic membranes of Prochlorothrix therefore represent a prokaryotic system that is remarkably similar, in structural terms, to the photosynthetic membranes found in chloroplasts of green plants.
Polarity and differentiation of human rectal adenocarcinoma cells in suspension and collagen gel cultures
Authors: Kirkland Susan C.
Published: April 2021

HRA-19a1.1. cells, derived from a primary human rectal adenocarcinoma, form polarized monolayers when grown on tissue-culture plastic. The apical membrane of the cells is in contact with the culture medium while the basolateral surface is attached to the plastic substratum. Cells cultured on non-tissueculture plastic form floating colonies. Cells within these colonies are orientated so that their apical membrane is in contact with the culture medium while the basolateral membrane faces the centre of the colony. When these colonies are embedded in collagen gel the cells organize to form glandular structures similar to those observed in xenografts of this cell line. In addition a reversal in the orientation of cell polarity is observed with the basolateral membrane now in contact with the collagen gel, while the apical membrane faces lumina within the colony. This interaction is specific to collagen gel, as in a control experiment where colonies are embedded in agarose gel, neither a reversal in polarity nor the formation of glandular structures is observed. These results demonstrate an induction of glandular organization in human rectal adenocarcinoma cells by collagen gel. In addition an increased absorptive cell differentiation and reversal in cell polarity is observed in response to collagen gel.
Modified hydroxyethylmethacrylate hydrogels as a modelling tool for the study of cell-substratum interactions
Authors: Bergethon Peter R. , Trinkaus-Randall Vickery , Franzblau Carl
Published: April 2021

The interactions between cells and their extracellular substratum environment are complex and difficult to study. Defined, synthetic substrata are valuable tools for experimentally determining the role of ionic and receptor-specific interactions between cells and their substrata. Hydrogels have been modified to contain stoichiometrically defined quantities of both positive and negative charge as well as specific proteins. These synthetic surfaces are water-rich matrices that possess hydroxyl groups, positive and negative ionized charges and native proteins, and can be considered as models of extracellular matrices on which an assessment of charge contribution and macromolecular content and specificity can be addressed with respect to cell-matrix interactions. This study shows that simple gels made of polyhydroxyethylmethacrylate do not support the spreading of cells but that the generation of copolymers by the addition of monomers that contain ionizable functional groups, will permit cell spreading. These simple modifications do not lead to cellular proliferation, yet when collagen is entrapped in the hydrogel substratum, proliferation occurs. The proliferative rate of cells grown on collagen-containing surfaces may be modified by altering the stoichiometry of the ionizable polymers used to make the surface. This study describes a synthetic, definable model for the study of cell-substratum interactions and control.
‘Corkscrewing’, as evidence for force generation within a detergent-extracted microtubule translocation system from insect ovaries
Authors: Stebbings H. , Sharma K. K.
Published: April 2021

Microtubule-based translocation channels within the ovaries of the hemipteran insect Notonecta have been isolated by microdissection, and then detergent-extracted to leave a bundle of some 30000 aligned microtubules. On addition of ATP and other hydrolysable nucleotides the microtubule bundle contorts into a helical configuration, a property we have called ‘corkscrewing’, before straightening again. This we believe to be indicative of force generation within the bundle.

Electrophoretic analysis of the bundle of native microtubules reveals many polypeptides apart from the tubulins, and a number of these comigrate with microtubule-associated proteins (MAPs), which copolymerize with tubulins in reassembled microtubules from the same system.

Corkscrewing does not occur if the microtubule bundle is pretreated with salt, a procedure that removes MAPs from microtubules, suggesting that the force is generated by a MAP or MAPs. In addition, certain minor polypeptides comprising the native microtubules are ATP-sensitive, a property expected of a microtubule motor.
Interaction of Drosophila 27000Mr heat-shock protein with the nucleus of heat-shocked and ecdysone-stimulated culture cells
Authors: Beaulieu J.-F. , Arrigo A. P. , Tanguay R. M.
Published: April 2021

The intracellular localization and expression of hsp27 (heat-shock protein 27) were investigated by cellular fractionation and immunofluorescence microscopy in Drosophila S3 cells. In unstressed cells, hsp27 is expressed in only 2 % of the cells, whereas following heat shock, during recovery or after induction by ecdysone, the protein is detected in all cells. Under all these conditions, hsp27 appears to be concentrated in the nuclear region as revealed by immunofluorescence. During heat shock, this hsp is localized primarily in the nucleus with an enrichment in the perinucleolar region. However, the cellular fractionation data indicate that the nature of hsp27 interaction with nuclear components greatly differs depending on whether or not cells were subjected to elevated temperatures. After heat shock, hsp27 is resistant to non-ionic detergent extraction. In cells allowed to recover at normal temperature and in those where its synthesis was induced by the molting hormone, ecdysone, this hsp is readily solubilized by detergent. These data suggest that, following heat shock, hsp27 may become physically associated with some nuclear component(s) that are resistant to detergent extraction.
Methotrexate-induced morphological changes mimic those seen after heat shock
Authors: Jackson Dean A. , Pearson Colin K. , Fraser Douglas C. , Prise Kevin M. , Wong Su Y.
Published: April 2021

The survival of cells cultured in medium containing the chemotherapeutic drug methotrexate (MTX) is related directly to drug concentration. Changes in DNA resulting from a severe imbalance in the cells’ nucleotide pools are thought to account for this cytotoxicity. We have attempted to clarify the gross biochemical changes that might lead to cell death. DNA strand breaks occur in cells treated with high concentrations of MTX but it is not clear that these are sufficient to account for cytotoxicity at lower doses. We observed dramatic changes in cytoskeletal morphology. Gross reorganization of the cytoskeleton is shown by immunolabelling but is highlighted dramatically when cells are lysed to leave ‘nucleoids’. The nature of the changes seen in MTX-treated cells is characteristic of the cells’ general stress response, seen originally following heat shock. This study shows that other factors, such as changes in cytoskeletal function, must be considered together with any contribution from DNA damage, in order to account for the lethal effects of MTX.
Cryotechniques in Biological Electron Microscopy
Authors: Gupta Brij L.
Published: April 2021

Our current knowledge of cell and tissue fine structure is mostly based on methods that, put bluntly, involve ‘poisoning, tanning and drying of living cells’ (Preface, p. xvii). The possibility that gross artefacts may well be generated by the conventional methods of chemical fixation, dehydration, embedding and staining etc. used for light and electron microscopy is implicit in the endless controversies that form a recurrent strand in the history of histology and cytology. The observation that low temperatures preserve living matter in a life-like condition for decades or even centuries must first have been made in the Ice Ages. The earliest attempts to avoid chemical fixation by freeze-drying date back to Altmann (1890, Die Elementarurgamsmen und ihre Beziehungen zu Zellen, Leipzig) and Mann (1902, Physiological Histology, Oxford). However, cells and tissues are up to 90 % water. The frustration of trying to freeze water without the formation of destructive ice crystals is delightfully summarized in this rhyme on the frontispiece from Wilhelm Busch (1832—1908):
The distribution of distinct integrins in focal contacts is determined by the substratum composition
Authors: Fath Karl R. , Edgell Cora-Jean S. , Burridge Keith
Published: April 2021

The distribution of two integrins, the fibronectin receptor and the vitronectin receptor, has been explored in an endothelium-derived cell line plated onto various substrata. On a fibronectin substratum, in the presence of serum, these cells develop focal contacts that contain the fibronectin receptor, whereas the vitronectin receptor is diffusely distributed over the cell surface. Conversely, cells plated onto vitronectin-coated coverslips concentrate only the vitronectin receptor within focal contacts. The accumulation of the vitronectin receptor within focal contacts also occurs when the cells are plated on uncoated coverslips but in the presence of serum. Therefore, we conclude that under normal culture conditions (i.e. in serumcontaining media), the vitronectin receptor is the predominant form of integrin involved in substratum adhesion. This conclusion is supported by experiments in which cells were cultured on fibronectin-coated coverslips in the presence of serum.

Initially these cells developed focal contacts containing only the fibronectin receptor. Within several hours, however, there was a progressive replacement of focal contacts containing the fibronectin receptor by focal contacts expressing the vitronectin receptor. After approximately 12 h in culture, most cells contained focal contacts expressing only the vitronectin receptor.

Focal contacts containing either the fibronectin or vitronectin receptor were both associated with the termini of stress fibres and contained the proteins talin and vinculin. These observations lead us to propose that the cell does not discriminate between these different integrins when assembling the cytoskeletal components at the cytoplasmic face of focal contacts.
In vitro effects of taxol on ciliogenesis in quail oviduct
Authors: Boisvieux-Ulrich Emmanuelle , Laine Marie-Christine , Sandoz Daniel
Published: April 2021

When induced by in vivo oestrogen stimulation, ciliogenesis continues in culture in vitro of quail oviduct implants. Ultrastructure of ciliogenic cells was compared after culture for 24 or 48 h in the presence or absence of 10−5 M-taxol. Taxol, which promotes polymerization and stabilization of microtubules, disturbed ciliogenesis, but formation of basal bodies was unaffected by the drug. Conversely, their migration towards the apical surface seemed to be slowed down or blocked and axonemal doublets polymerized onto the distal end of cytoplasmic basal bodies. They elongated and often constituted a more or less complete axoneme, extending between organelles in various orientations. These axonemes, often abnormal, were not surrounded by a membrane, with the exception of the transitional or neck region between the basal body and axoneme. The formation of membrane in this area resulted from the binding of some vesicles to the anchoring fibres of the basal body. They fused in various numbers, occasionally forming a ring, at the site of the transitional region, and exhibited the characteristics of the ciliary necklace. The association of basal bodies with vesicles or with the plasma membrane appeared to be a necessary signal for in situ polymerization of axonemal doublets.

In addition, taxol induced polymerization of numerous microtubules in the cytoplasm, especially in the apical part of the cell and in the Golgi area. This network of microtubules may prevent basal body migration.
The secretory vesicle in living Paramecium is acidic
Authors: Busch Gerald R. , Satir Birgit H.
Published: April 2021

In Paramecium, secretory proteins are packaged within membrane-bounded vesicles in a condensed form. This form expands when the proteins are released. We have now determined that a proton gradient is present in the secretory vesicles of living Paramecium. Acridine Orange, used as an in vivo indicator of acidic compartments, stained the secretory vesicles in both wild-type and mutant cells. Addition of the two agents that dissipate proton gradients (protonophores), namely, 2,4-dinitrophenol (DNP) and carbonylcyanide m-chlorophenyl-hydrazone (CCCP), eliminated this staining. Washed cells re-established their intravesicular acidity. Effects of sodium azide on vesicular acidity suggest that proton transport in these vesicles involves an ATP-dependent mechanism.
Cell growth kinetics, division asymmetry and volume control at division in the marine dinoflagellate Gonyaulax polyedra: A model of circadian clock control of the cell cycle
Authors: Homma K. , Hastings J. Woodland
Published: April 2021

A new method of determining the dependence of cell growth on the initial cell volume in the absence of cell division is presented. The assumptions are that volume in a certain period of time is either increasing or decreasing, but not both, and is independent of the history of cells. Applying this method to Gonyaulax polyedra in a 12 h light-12 h dark cycle, growth in volume between the 3rd and 12th hours of the light period is found to be more exponential-like than linear. The magnitude of growth in the time period is determined solely by cell volume and environmental conditions, not by cell age. All cells decrease in volume slightly in the dark from the 12th to 23rd hour, and then increase a little from the 23rd to 3rd hour of the following day. Cell division in this species is significantly asymmetric, and the extent of asymmetry is estimated mathematically. Simulations based on the growth patterns and the asymmetric division reveal that cell division must at least partly depend on the volume of cells.

The dependence of conditional cell division probability on cell volume is then experimentally determined. The probability is zero up to a certain cell volume, and then it gradually increases to a plateau level, which is less than unity. Neither the strict size control model nor the transition probability model is fully consistent with the observed shape of the conditional probability function. A hybrid model postulating a ‘sloppy’ critical volume with a constant probability of division above that volume adequately accounts for the conditional probability. With the use of the observed volume growth law, cell division dependence on volume, and the extent of asymmetry in cell division, cell volume distributions are successfully simulated for cells growing in a 12 h light-12 h dark cycle. Another simulation reveals that the true coefficient of variation in generation time is 33%. On the basis of these findings, a model of the cell cycle is presented that incorporates the circadian clock as a cyclic G1 phase. According to this scheme, cells satisfying the minimum cell volume requirement between the 12th and the 18th hour probably exit to the replication/segregation sequence ending in division, and re-enter the cyclic portion after a fixed time interval.
Cell volume and dry weight of cultured Tetrahymena
Authors: Hellung-Larsen Per , Andersen Anders Poul
Published: April 2021

Cultures of Tetrahymena pyriformis, T. hegewishi and T. malaccensis have been studied with regard to control of cell volume and cellular dry weight. Cell volume was measured on cells suspended in 0-9% sodium chloride + 0 ·1% sodium azide using a Multisizer cell counter (Coulter). Tetrahymena were grown at different temperatures and under various up- or downshift conditions. In all cases the changes in cell volume are paralleled by changes in cellular dry weight. The volume and the dry weight of a Tetrahymena cell are determined by the particular medium and the growth temperature. Large cells are seen in concentrated media and at low growth temperatures resulting in cell volumes up to 17000 μm3, whereas starving cells decrease gradually towards 700 μm3 or even smaller sizes. It is proposed that lag phase observed at up- and downshift is to a large extent due to the necessary adjustment of the cell volume to the new conditions.
Three-dimensional arrangements of chromatin and chromosomes: Old concepts and new techniques
Authors: Appels R.
Published: April 2021

The studies of early cytologists, well before the turn of this century, indicated that the positions of mitotic chromosomes in a particular metaphase cell correlated with their respective positions in preceding cell divisions. Observations of this type led to the concept that metaphase chromosomes were not simply aggregations of dispersed chromatin. Furthermore, when it became clear that chromosomes were the carriers of the genetic material many ideas developed relating the arrangement of chromosomes to gene expression in nuclei. A major problem in analysing interphase nuclei was the difficulty in visualizing chromosomes at this stage in the cell cycle. Recent advances in combining the techniques of molecular biology with modifications to the optical microscope and computer image enhancement, analysis and interpretation have revolutionized the capability of studying the very old problem of whether order exists within the eukaryote nucleus.
The effects of tunicamycin, mevinolin and mevalonic acid on hmg-coa reductase activity and nuclear division in the myxomycete Physarum polycephalum
Authors: Engström Wilhelm , Larsson Olle , Sachsenmaier Wilhelm
Published: April 2021

The effects of two inhibitors of 3-hydroxy 3-methyl glutaryl-coenzyme A reductase (tunicamycin and mevinolin) on nuclear division in the myxomycete Physarum polycephalum were examined. Tunicamycin exerted a minor effect on division in synchronized cultures, whereas mevinolin delayed the second, third and fourth nuclear divisions with increasing efficiency. Mevinolin also appeared to be the more potent inhibitor of HMG-CoA reductase, which catalyses the rate-limiting step in the biosynthesis of cholesterol and other isoprene derivatives. These effects of mevinolin could be partially reversed by the addition of mevalonate, suggesting that mevinolin exerts its inhibitory effects on Physarum nuclear division by decreasing the activity of HMG-CoA reductase.
Observations on ultracentrifuging wild-type and mutant (cdc2.33) cells of Schizosaccharomyces pombe
Authors: Khar A. , Mitchison J. M.
Published: April 2021

Ultracentrifuging (400 000 g for 4–6 h at 4 °C) living wild-type cells of the fission yeast Schizosaccharomyces pombe moves the nucleus towards the ends of the cells but scarcely affects their viability. However, in the long cells produced by growing the mutant cdc2.33 for 4–6 h at the restrictive temperature (36–5°C), ultracentrifuging (as above) gives an intense fluorescence with DAPI in about half of the cytoplasm in about 80% of the cells. This is probably nuclear DNA that has moved into the cytoplasm, both because of the DAPI stain and because it is removed by DNase treatment. These cells ultimately divide and are viable, and we suggest that the extended cytoplasmic DNA returns to the nucleus.
Characterization of a heat-resistant strain of Tilapia ovary cells
Authors: Wang H. C. , Chen J. D. , Li G. C. , Yew F. H.
Published: April 2021

Tilapia ovary cells (TO-2) cease to proliferate when moved from normal growth temperature of 31 °C to 37°C, and arrest in G1 and G2 phases of the cell cycle. The ability of the arrested cells to re-enter the cell cycle when restored to 31 °C decreases inversely with time spent at 37°C. A heat-resistant strain, TO-37c, cloned from the surviving fraction of TO-2 after heat treatment, has been found to re-enter the cell cycle with greater facility and to have a higher rate of survival. TO-37c cells have a smaller cell volume than TO-2 and show a distinct morphology at 37°C. Most of the heat-shock proteins (hsps) induced on temperature change were similar, but in TO-37c the decline in the synthesis of a 27×103Afr hsp was faster and a 37°C-specific 60×103Mr hsp was missing. Ultraviolet (u.v.) sensitivity was slightly affected if heat treatment was given after irradiation. However, when cells were preheated and then u.v. irradiated, the u.v. sensitivity increased sharply for TO-2 cells but not for TO-37c.