bluuebunny/crossref_metadata_2025 huggingface dataset:
Mutual cohesion and cell sorting-out among four species of cellular slime moulds
Authors: Nicol A. , Garrod D. R.
Published: April 2021

Interspecific cell cohesion among 4 species of cellular slime moulds, Dictyostelium discoideum, D. mucoroides, D. purpureum and Polysphondylium violaceum has been studied. Binary mixtures of aggregation-stage cells of the 4 species were shaken in suspension, one species of each pair being labelled with PH]thymidine. Cell aggregates were sampled at intervals over 24 h and their composition examined by autoradiography. The following results were obtained: (i) Cells of each species were capable of cohesion with those of the other 3 species, (ii) In general cells of both species in any mixture were present in aggregates after 1 h, but were not localized according to species, (iii) Within 8-h aggregates cells of different species were regionally localized, i.e. sorting-out appeared to have taken place, (iv) 24-h aggregates were more varied: in mixtures of Dictyostelium species, the different species were localized within the aggregates; in mixtures of Dictyostelium species with Polysphondylium, there was a tendency for cells of the different species to become segregated into completely separate aggregates.

The significance of these results in relation to both previous descriptive work and recent biochemical studies on the mechanism of slime mould cell cohesion is discussed.
The distribution of actin cables and microtubules in hybrids between malignant and non-malignant cells, and in tumours derived from them
Authors: Watt Fiona M. , Harris H. , Weber K. , Osborn Mary
Published: April 2021

Cell fusion provides a genetic test for linkage between cellular phenotypic markers and malignancy. We have examined hybrid cells in which malignancy is suppressed and malignant segregants derived from them, to test whether the reappearance of malignancy is regularly associated with loss or abnormality of actin cables or microtubules. Immunofluorescence studies did not reveal any difference between the malignant and non-malignant hybrids in the number and distribution of microtubules that they contained. All the hybrids, whether tumorigenic or not, contained elaborate patterns of cytoplasmic microtubules. Furthermore, no consistent relationship was observed between the absence of actin cables and malignancy.
Divalent cation stimulation of in vitro fibre assembly from epidermal keratin protein
Authors: Fukuyama Kimie , Murozuka Takashi , Caldwell Russell , Epstein William L.
Published: April 2021

Keratin was extracted from purified cornified cells of newborn rats in Tris-HCl-buffered 8 M urea containing β-mercaptoethanol. Microfilaments were assembled in vitro by reducing the ionic strength of buffer and the urea concentration.

One millimolar concentration of KC1 and NaCl did not affect filament formation, but the same concentration of divalent cations greatly altered this process. CaCl2 and MgCl2 induced gelation of keratin by formation of bundles of biréfringent macrofilaments. ZnCl2, CuSO4 and HgCl2 formed greater numbers of macrofilaments and the protein aggregated.
Stimulation of dendritogenesis in the epidermal melanocytes of newborn mice by melanocyte-stimulating hormone
Authors: Hirobe Tomohisa
Published: April 2021

The number of dendrites and the total length of dendrites in the epidermal melanocytes positive for the dopa reaction were shown to increase when newborn mice were injected with α-MSH or DBc-AMP. Moreover, both indices of the degree of dendritogenesis increased when skin expiants of newborn mice were cultured in medium containing α-MSH or DBc-AMP. Electron-microscopic observation showed that the number of melanosomes was also increased by α-MSH treatment. Many mature melanosomes were observed in the dendrites of the epidermal melanocytes of α-MSH-injected mice. Highly dendritic melanocytes seem to be the cells stimulated by MSH to form melanosomes and translocate them to dendrites. Dendritogenesis stimulated by the hormone was suppressed by actinomycin D or cycloheximide, suggesting that the dendritogenesis in the epidermal melanocytes requires de novo transcription and translation.
Unidirectional regeneration is an intrinsic property of longitudinal microtubules in Tetrahymena-an in vivo study
Authors: NG Stephen F.
Published: April 2021

The cortex of Tetrahymena contains a regular array of longitudinal microtubular bands (lms) next to basal body rows running from pole to pole. The lm exhibits a predominant unidirectionality in assembly. The direction of regeneration following breakage of the microtubules is from posterior to anterior of the cell. When the lm and the accompanying basal body row are rotated 180 ° (inverted), so that their polarity is opposite to that of the cell, the predominant direction of regeneration exhibited by the inverted lm is from anterior to posterior. This shows that the lm has an inherent direction of regeneration independent of cellular polarity. This implies that the microtubules constituting the lm have an intrinsic property which controls the direction of assembly. This finding is in accord with the in vitro demonstration using Chlamydomonas flagellar fragments. On the basis of this finding and also the possible pattern of arrangement of the microtubules constituting the lm, it is suggested that growth of the lm involves both elongation of pre-existing microtubules constituting the lm and also laying down of new ones.
Preaggregative cell motion in Dictyostelium
Authors: Potel Michael J. , Mackay Steven A.
Published: April 2021

The motions of a large number (495) of preaggregative D. discoideum NC-4 cells in sparse fields are recorded on time-lapse film and analysed using a specially constructed computer graphics system. All films are produced under a standard set of conditions, so that the range of cell behaviours under given conditions can be characterized. The mean velocity of preaggregative D. discoideum NC-4 is 7·19 μm/min. The mean velocity time course has a significant early peak at about 3 h. The distribution of mean velocities is fairly broad with a long high velocity tail. A modified random walk model using the parameters diffusion constant and persistence time describes well the changes in cell direction with time. Persistence can be described as an exponentially distributed ‘memory’ of movement direction, with a mean of 4·89 min. High velocity cells never have long persistence times, and persistence time shows no relationship with age. A nearest neighbour model of cell spacing shows that cells are randomly (Poisson) distributed at low densities. Measurements of cell contacts are compared to a simple model of contact frequency based on the kinetic theory of gases to show that cells at low densities have an affinity for making collisions. The length of contact durations is indicative of some mechanical adhesion between cells, and cells in contact move significantly though not dramatically slower. A cross-correlation analysis shows that the various parameters of motion are significantly interrelated in numerous ways. Finally mutants and strains related to D. discoideum NC-4 exhibit a number of new behaviours, suggesting that motion is a distinctive characteristic of cell type.
Effect of concanavalin A dose, unbound concanavalin A, temperature, ca2+ and mg2+, and vinblastine on capping of concanavalin A receptors of human peripheral blood lymphocytes
Authors: Bhalla D. K. , Hunt C. V. , Kapur S. P. , Anderson W. A.
Published: April 2021

The capping of Concanavalin A (Con A) receptors induced by Con A was studied using human peripheral blood lymphocytes. The effects of Con A dose (5–100 μg/ml), pretreatment at 4 °C, unbound Con A, extracellular Ca2+ and Mg2+ and vinblastine were evaluated using Con A-horseradish peroxidase and electron microscopy. Lymphocytes incubated with Con A at 4 °C and fixed with glutaraldehyde exhibited Con A-horseradish peroxidase around the entire cell periphery. After raising the temperature to 37 °C, the Con A-horseradish peroxidase moved to form a cap at one pole of the cell and subsequently underwent endocytosis. Capping of Con A receptors induced by Con A at 37 °C was observed only at low Con A concentrations in the presence of unbound Con A and extracellular Ca2+ and Mg2+. Increased capping was found after pretreatment of cells with Con A at 4 °C, removing unbound Con A and/or removing extracellular Ca2+ and Mg2+, and by treatment with vinblastine. Following removal of both unbound Con A and extracellular Ca2+ and Mg2+, the percentage of capped cells at 37 °C was the same as on pretreatment at 4 °C under the same conditions. While pretreatment at 4 °C caused the breakdown of microtubules, removal of unbound Con A and/or extracellular Ca2+ and Mg2+ had no morphological effect on microtubules or microfilaments. Following exposure of lymphocytes to vinblastine and removal of unbound Con A, capping of Con A receptors by Con A was observed in over 90 % of cells at all Con A dosages. However, when cells were exposed to vinblastine in the presence of unbound Con A the formation of Con A caps was either partially or completely inhibited.
Plasmalemma invaginations of Physarum dependent on the nutritional content of the plasmodial environment
Authors: Achenbach Friedhelm , Naib-Majani Wallid , Wohlfarth-Bottermann Karl Ernst
Published: April 2021

Quantitative estimates of plasmalemma invaginations in plasmodial veins of Physarum polycephalum were made under different conditions of nutrition. Pronounced differences were observed dependent on the nutritional content of the substrate. There was a decided increase in the number of plasmalemma invaginations in plasmodial veins grown on substrates containing absorbable food substances compared to veins migrating on non-nutrient substrates. This observation supports the proposition that the nutritional content, rather than the physical properties, of the substrate is the decisive factor for the formation of plasmalemma invaginations. The invaginations are believed to be concerned with the uptake of non-particulate food substances.
Increase in macromolecular amounts during the cell cycle of tetrahymen a a contribution to cell cycle control*
Authors: Cleffmann Günter , reuter Wolf-otto , seyfert Hansmartin
Published: April 2021

Increases in RNA, protein and cell size were determined cytophotometrically during the cell division cycle of Tetrahymena. For these parameters different patterns were found. RNA accumulates slowly during G1 period and faster during macronuclear S. This agrees with the changing uridine incorporation rate which is at least partly related to the varying macronuclear DNA amount. Increases in protein content and cell size occur mainly during G1and G2. This pattern was confirmed by determining the RNA : protein ratio in individual cells. It is minimal at the end of the G, period. These findings and evidence from the literature suggest that initiation of DNA replication is under negative control by the relative RNA content of the cell.
Survival of cells implanted in the embryonic chick limb bud: A difference between normal and malignant rat brain cells
Authors: Tickle C. , Crawley A. , Roscoe J. P.
Published: April 2021

Cells from normal rat brain tissue did not survive and few cells could be found 1 d after grafting. In contrast, cells from a glioma and a carcinogen-treated rat brain survived well and many mitoses were observed. These malignant cells also invaded the limb. The behaviour of normal and malignant cells was followed at shorter times after grafting and some invasion by the normal cells was detected. The first signs of degeneration of normal cells were apparent around 7 h after grafting, and after this the grafts progressively deteriorated. These results support the idea that the ability of cells to survive and grow in embryonic tissues is a characteristic of malignant cells. The findings are discussed in relation to mechanisms of tumour formation.
A ligand-receptor model for the cohesive behaviour of Dictyostelium Discoideum axenic cells
Authors: Jaffe Alida R. , Swanf Alma P. , Garrod D. R.
Published: April 2021

Axenically grown cells of D. discoideum Ax-2 harvested in the log phase of growth, cohere rapidly when shaken in phosphate buffer. After 3.5 days in the stationary phase of growth, cells become completely non-cohesive. Although they do not stick to each other, stationary phase cells do stick to both log phase cells and aggregation-competent cells. The cohesion of stationary phase cells with these other 2 cell types is inhibited by both EDTA and the low-molecular-weight factor which we have previously demonstrated in stationary-phase growth medium.

There is a decline in the sensitivity of slime mould cell cohesion to the low-molecular-weight inhibitory factor as the cells become aggregation-competent. This effect parallels the developmentally-regulated decline in sensitivity to EDTA. The low-molecular-weight inhibitor is not a chelating agent, however. The effect of the inhibitor seems to be specifically against contact sites-B mediated cohesion. We suggest that the simplest cohesive mechanism which can explain our results, is that the EDTA-sensitive cohesion of log phase cells could be dependent on a ligand-receptor system.
Dibutyryl cyclic amp suppresses mobility of embryonic chick heart cells in aggregates
Authors: Gershman Howard , Weis Geri , Barstow Nancy
Published: April 2021

The intermixing of chick embryonic heart ventricle cells was studied in cellular aggregates as a function of embryonic age of the cells. Cell mobility, as measured by intermixing of radiolabelled and unlabelled cells, was high in cells derived from young embryos: 5.36 ± 1.05 cell diameters per 2.5 days for 6-day-old heart ventricle cells. During development, mobility steadily declined to 1.56 ±0 24 cell diameters per 2.5 days for 18-day old cells. Treatment of aggregates with 1.0 mM theophylline plus 1.2 mM dibutyryl cyclic AMP resulted in greatly decreased mobility, particularly in aggregates of the more mobile younger cells. Depending on the embryonic age of the heart ventricle cells, this treatment reduced mobility by 45.3 to 89.4%. These data are consistent with an age-dependent decrease in intrinsic mobility superimposed upon a contact-paralysis mediated inhibition of movement present in solid tissues. In addition, the sensitivity of heart ventricle cells to inhibition by agents that increase intracellular cyclic AMP levels suggest that this is another possible inhibitory mechanism, although its physiological significance has not been established.
Stem cell growth and differentiation in Hydra attenuata: II. Regulation of nerve and nematocyte differentiation in multiclone aggregates
Authors: Sproull Frederick , David Charles N.
Published: April 2021

The differentiation of nerve cells and nematocytes from interstitial stem cells in Hydra has been investigated under conditions of changing stem cell density. Interstitial stem cells were cultured in a feeder layer system consisting of aggregates of nitrogen mustard-inactivated tissue. The aggregates were seeded with varying numbers of stem cells from 10 to 400 per aggregate; between 4 and 7 days later the rates of nerve and nematocyte differentiation were measured. Nerve differentiation was scored by labelling the stem cell population with [3H] thymidine and counting labelled nerve cells after 48 h. Nematocyte differentiation was scored by counting nests of 4 proliferating nematoblasts. In both cases the numbers of differentiating cells were normalized to the size of the stem cell population.

The results indicate that the rate of nematocyte differentiation increases as the concentration of stem cells increases in aggregates; under the same conditions the rate of nerve differentiation remains essentially constant. To calculate the numbers of stem cells entering each pathway per generation, a computer was programmed to simulate the growth and differentiation of interstitial stem cells. Standard curves were prepared from the simulations relating the rates of nerve and nematocyte differentiation to the fraction of stem cells committed to each pathway per generation. The rates of nerve and nematocyte commitment were then estimated from the experimentally observed rates of differentiation using the standard curves. The results indicate that nerve commitment remains constant at about 0·13 stem cells per generation over a wide range of stem cell concentration. Nematocyte commitment, by comparison, increases from 0·15 to 0·21 stem cells per generation as stem cell concentration increases in aggregates. The fact that the ratio of nerve to nematocyte commitment changes under our conditions suggests that stem cell commitment is not a stochastic process but subject to control by environmental stimuli.
Immaturity substances in paramecium primaurelia and their specificity
Authors: Miwa Isoji
Published: April 2021

Cells of Paramecium primaurelia in the immaturity period of the life cycle contain substances which repress the expression of mating ability when introduced into mature cells. When the immature cytoplasm of P. primaurelia was injected into mating-reactive cells of P. tetraurelia, P. caudatum and P. timicronucleatum, immaturity was also induced in them. But the immature cytoplasm of P. primaurelia was ineffective when injected into mature cells of P. bursaria. When the immature cytoplasm of P. bursaria was injected into mating-reactive cells of P. primaurelia and P. tetraurelia, no difference from the control was observed. When the immature cytoplasm of P. caudatum was injected into mating-reactive cells of P. pri maurelia and P. tetraurelia, immaturity was induced in cells of the latter 2 species.
Vesicles in guard-cell walls and their possible roles in the stomatal mechanism
Authors: Cork Robert John , Nelmes Brenda J.
Published: April 2021

A variety of vesicular inclusions have been, observed in guard-cell walls. They have been seen in a number of species and are mostly membrane-bound. They appear confined to the upper and ventral walls of the guard cell. A number of possible origins and functions are discussed. They may be involved in wall deposition or cuticle formation possibly in a role similar to ectodesmata. They also may serve to increase the wall-plasmalemma interface to enhance the movement of ions during the stomatal mechanism.
A cytochemical and radioautographic study of the ultrastructural organization of puff-like fibrillar structures in plant interphase nuclei (Allium porrum)
Authors: Lafontaine J. G. , Luck B. T. , Dontigny D.
Published: April 2021

Loose, fibrillar, spherical structures have been observed during recent years in interphase nuclei of both animal and plant cells. These nuclear formations have been referred to as karyosomes, fibrillar bodies, micropuffs and centromeres. In order to gain further information on the nature of these structures, a cytochemical and radioautographic investigation was undertaken using plant meristematic cells (Allium porrum). For that purpose roots were fixed with either formaldehyde or glutaraldehyde in order to carry out cytochemical tests for DNA, RNA and proteins. Certain of the preparations were also first digested with DNase, RNase or proteinase K and then stained according to different procedures. Other specimens were labelled with thymidine for high-resolution radioautographic observations. Staining with diaminobenzidine (DAB) revealed that these nuclear puff-like formations consisted partly of a loose fibrillar meshwork containing nucleic acids. Part of this fine fibrillar reticulum persisted whether the preparations were digested with DNase or RNase before staining with DAB, thus indicating that these nuclear structures contained both DNA and RNA. The fact that these formations incorporate thymidine furnished additional support for the view that they correspond to specific chromosome segments. Staining with ethanolic phosphotungstic acid or digestion of specimens with proteinase K showed that these loose fibrillar structures also consisted of proteins.

Judging from their ultrastructure, their association with the chromatin reticulum as well as from their cytochemical characteristics, these nuclear formations most likely correspond to centromeres.

In view of the presence of DNA within these structures, it is possible to distinguish them from other equally spherical nuclear formations, observed in certain plant species, that have generally been referred to as karyosomes or micronucleoli and that appear to consist of ribonucleoproteins.
Yolk transport in the ovarian follicle of the hen (Gallus domesticus): Lipoprotein-like particles at the periphery of the oocyte in the rapid growth phase
Authors: Perry M. M. , Gilbert A. B.
Published: April 2021

Thin sections of the oocyte periphery and surrounding granulosa layer from 1–5-day preovulatory follicles were examined by transmission electron microscopy. With the use of certain procedures in tissue preparation, notably the tannic acid method, numerous particles in the range of 15–40 nm with a mean diameter of 27 nm were observed both extra- and intracellularly. The particles were abundant in the granulosa basal lamina, in the spaces between the granulosa cells and in the perivitelline space. They appeared to adhere to the oolemma as a continuous double layer which was also observed to line the coated vesicles, 200–350 nm in diameter, invaginating from the oolemma. The layer of particles was not found on the plasma membranes of the granulosa cells, nor were particles present within the cells. In the peripheral cytoplasm of the oocyte the yolk spheres, ranging upwards from 250 nm diameter, were membrane-bound and contained tightly packed particles similar to those on the oolemma. Bodies displaying features intermediate between coated vesicles and yolk spheres suggested that, on entry into the cell, loss of the cytoplasmic coat and obliteration of the vesicular lumen gave rise to nascent yolk spheres which then fused together to form the larger spheres. The extracellular layer, coated vesicles and smaller yolk spheres were absent in oocytes fixed after a 10-min delay.

The evidence indicated that 27-nm particles were transferred from the basal lamina to the oocyte surface via the intergranulosa cell channels, incorporated into the cell by adsorptive endocytosis and then transferred to the yolk spheres with little morphological alteration. The identity of the particles with very low density lipoproteins, the major components of the yolk solids, was discussed.
Pseudopodium induction by the action of quaternary ammonium ions on Amoeba proteus
Authors: Brewer J. E. , Bell L. G. E.
Published: April 2021

Some aliphatic long-chain quaternary ammonium compounds and choline derivatives have been examined for their ability to induce pseudopodia from Amoeba proteus. The reaction involved in pseudopodium induction is believed to be between the quaternary nitrogen cations and polysaccharides on the cell surface. Not all of the carboxyl groups of the polysaccharide are involved in this reaction. The mechanism of pseudopodium induction is discussed in terms of changes in the surface charge and the permeability of the cell membrane.
The effect of dissolved oxygen partial pressure on the growth and carbohydrate metabolism of mouse LS cells
Authors: Kilburn D. G. , Lilly M. D. , Self Daphne A. , Webb F. C.
Published: April 2021

Batch cultures of mouse LS cells were grown in suspension at controlled dissolved oxygen partial pressures (pO2). At low pO2 (1·6 mmHg) the growth and respiration rates and the final cell population were all limited. At high pO2 (320 mmHg), cell division was inhibited after an initial doubling of the cell number. At intermediate values of pO2, the growth rate was constant but the final cell population varied. Within the pO2 range of 40 –100 mmHg, the final cell population was constant and maximal at 1·2 × 106 viable cells/ml. Except at 320 mmHg pO2, about 90 % of the glucose consumed served as an energy source and could be accounted for as lactate and CO,. In the culture at 320 mmHg, only 60 % of the glucose consumed could be accounted for in this way. During growth the production of lactate and pyruvate was highest at low pO2. A sharp increase in lactate production was observed as logarithmic growth ceased in each culture, except at high pO2 (160 mmHg). These observations indicate that pO2 markedly influences cell growth and carbohydrate metabolism in these cells.
Endocytosis of sugars in embryonic skeletal tissues in organ culture: I. general introduction and histological effects
Authors: Fell Honor B. , Dingle J. T.
Published: April 2021

The addition of sucrose to a chemically denned culture medium caused intense cytoplasmic vacuolation of the perichondrial, oesteogenic and articular cartilage cells of limb-bone rudiments from day embryonic chicks grown in organ culture. The rest of the cartilage appeared unaffected by the sugar. The osteocytes were intensely vacuolated; the bone matrix was much less dense than that of the controls and had an abnormal fibrillar structure. When the explants were transferred to medium without sucrose, after 6 days vacuolation had almost disappeared.

The effect of the sucrose was dose-dependent; at a concentration of 0·32M the sugar was highly toxic; at 0·16M the explants survived and vacuolation of the chondrocytes extended further into the cartilage than at 0·08M. A similar vacuolation of the cells in response to sucrose was seen in the isolated shafts of the limb-bones and in the mandibular rami from 11- to 13-day embryos; in the sucrose-treated explants osteogenesis was arrested and in places the bone showed osteolytic changes.

In the absence of glucose, day limb-bone rudiments failed to grow and rapidly degenerated in medium containing 0·08 M sucrose, indicating that sucrose was very little if at all metabolized. Explants of day rudiments grown for 8 days in the presence of 0·08M glucose showed no vacuolation; dextran had some effect, and both mannitol and sorbitol caused vacuolation.
Studies on the fine structure of muscle fibres and contained crystalloids in basal socket muscle of the entoproct, Barentsia gracilis
Authors: Reger J. F.
Published: April 2021

Basal socket muscle fibres of Barentsia gracilis are morphologically similar to invertebrate muscles classified as slow, tonic-type muscles. They are divisible into a non-contractile bulbous and a contractile myofilamentous portion, are innervated on their non-contractile surface, and are obliquely striated. The electron density and myofilament packing vary from fibre to fibre. Some muscle fibres appear degenerate in that they contain disorganized-appearing myofilaments and electron-dense bodies morphologically reminiscent of autophagosomes found in cells undergoing cytolysis.

A distinguishing feature of muscle fibres observed in B. gracilis is the presence of crystalloids, morphologically reminiscent of protein storage crystalloids found in other cell types. These crystalloids are seen to be composed of 30—70 A thick, helically shaped filaments arranged in a hexagonal lattice. Filaments have a pitch of 130—150 A and a tilt-angle of 35–45 degrees. Crosslinks occur between adjacent filaments at regular intervals. Crystalloids appear to be formed in the bulbous portion of muscle cells. Constituent, 30–70 A filaments appear to branch from crystalloids and are found free in the myofilamentous area of muscle fibres.

The above evidence, coupled with evidence elsewhere in the literature, suggests that the crystalloids may be a storage form of myofilament precursor which relate either to myogenesis or to cyclic regenerative and degenerative phenomena known to occur in Entoprocts, including B. gracilis.
Muscle attachment related to cuticle architecture in apterygota
Authors: Caveney S.
Published: April 2021

In Apterygota muscles are attached to the cuticle by a series of discrete structures. The junction of the muscle and epidermal cells is demarcated by regular interdigitations of the two tissues, with desmosomes lining these processes. Within the epidermal cells, microtubules link up the desmosomes of the interdigitated region with dense material associated with cone-like depressions in the apical plasma membranes of the epidermal cells. Each of these ‘conical hemidesmosomes’ is situated opposite a pore canal. From within each cone, an electron-dense ‘muscle attachment fibre ‘extends up the corresponding pore canal through the procuticle and is inserted on the epicuticle. There is no direct link between the microtubules and the muscle attachment fibres. The muscle attachment fibres are slightly elliptical in cross-section, and are twisted, this twist being in phase with the orientation of the chitinprotein microfibrils forming the lamellae of the procuticle. The attachment fibres are straight, and not helically arranged; patterns obtained in oblique sections of procuticle including these structures support the twisted ribbon model of pore canal shape. The cuticle, particularly in Thysanu?an and Dipluran intersegmental membrane, displays the parabolic patterning typical of softer insect procuticle and procuticle deposition zones. The epicuticular insertion of the muscle attachment fibre is characterized by a pit in the cuticulin layer, the fibre passing through the middle of this pit.

The microtubule-associated conical hemidesmosomes appear to be cytoskeletal in function. The muscle attachment fibres are rigid structures which are not digested by the moulting fluid enzymes. New muscle attachment fibres may only become attached to the epicuticle during its formation. The structures described in regions of muscle attachment in Apterygota are similar to those recorded for other arthropods.
Nuclear ultrastructure of the transforming lymphocyte during inhibition of deoxyribonucleic acid synthesis with hydroxyurea
Authors: Milner Gillian R.
Published: April 2021

The pattern of decondensation of heterochromatin in the transforming lymphocyte was found to be unaffected by hydroxyurea although DNA synthesis, which normally accompanies the latter part of this decondensation, was greatly inhibited. It is suggested that metabolic inhibition of DNA synthesis may result in atypical sites of DNA synthesis when the inhibitor is removed, since such sites are normally partly governed by an ordered sequence of decondensation of heterochromatin.
The nutritional relationship of Anemonia Sulcata (pennant) and its dinoflagellate symbiont
Authors: Taylor D. L.
Published: April 2021

High resolution autoradiography in the optical and electron microscopes has been used to define the nature of the nutritional relationship between Anemonia sulcata and its algal symbiont. Grain counts from these autoradiographs have been examined quantitatively, and the results compared with those obtained from an in vitro analysis of the excreted products of the symbionts. These investigations clearly indicate that a system of carbon translocation between the alga and the host does exist in situ, and that over 60 % of the carbon fixed in photosynthesis is transferred to the host under the conditions of these experiments.
Mitochondrial associations with specific microtubular components of the cortex of Tetrahymena thermophila : II. response of the mitochondrial pattern to changes in the microtubule pattern
Authors: Aufderheide Karl J.
Published: April 2021

Mitochondria in Tetrahymena thermophila are known to associate with the cell cortex in asymmetrical patterns corresponding to the asymmetrical organization of the microtubular components of the cortex. Specific mitochondrion-microtubule associations are seen at the light-microscope and ultrastructural levels. The hypothesis that the mitochondrial pattern is determined by the microtubular pattern was tested. Using the phenotypes of various mutations to generate changes in the organization of the cortex, the response of the mitochondrial pattern to the cortical change was assayed. The results consistently show that changes in the local organization of the cortical microtubule systems are followed by a corresponding change in the cortical mitochondrial pattern. However, the mitochondrial pattern is unaffected by a mutation which changes the ‘long-distance’ patterning of certain organelles, but which does not influence the local microtubular organization. Thus, the data support the hypothesis that there is a causal relationship between the arrangement of the cortical microtubules and the corresponding mitochondrial pattern.
Formation of cell-to-substrate contacts during fibroblast motility: An interference-reflexion study
Authors: Izzard Colin S. , Lochner Linda R.
Published: April 2021

The formation of close contacts and focal contacts (co. 30 nm and 10–15 nm separation distance respectively) has been studied during the movement of chick heart fibroblasts on planar substrates using interference-reflexion microscopy, and evaluated in the context of spreading and net movement. During spreading the overall advance of the margin of the close contact is steady, punctuated by periods in which it remains stationary, and only 5% of the time is spent withdrawing in contrast to the extreme leading edge. The close contact advances only where a lamellipodium has first extended free of the substrate (⩾100 nm separation distance) ahead of the existing close contact. The new close contact is formed by the lamellipodium lowering to the substrate either progressively from its base forward or distally in patches which later join with the main close contact. New focal contacts are formed successively ahead of existing ones, either by microspikes or lamellipodia contacting the substrate locally ahead of the close contact, or within the close contact usually immediately, but not more than 1–2 μm, behind its margin. Examining the cell margin alternately with interference-reflexion and differentialinterference contrast showed that the formation of the focal contact was preceded in 90% of the cases by the development of a linear structure in the form of a microspike (as expected), a short projection (<2 μm long) of the lamellipodium, or a fibre within the lamellipodium, each of which could be traced to the cytoplasmic fibre typically associated with the focal contact. Stress fibres subsequently developed centripetally from these initial fibres. The different forms of the linear structure which preceded the focal contact were interchangeable, giving rise to one another, and we have evaluated that the structure common to each is probably a short bundle of microfilaments.

The following features indicate that the close contact plays a primary role in marginal spreading: it is lost when spreading ceases; it is reformed when spreading resumes but only under the newly spread area; the advance of the margin of the thicker leading lamella closely follows that of the close contact; the advance of both can occur ahead of and is thus independent of existing focal contacts and associated stress fibres. We propose that the close contact provides the adhesion required to transmit to the substrate the forces involved in the forward movement of the marginal cytoplasm. The continual formation of focal contacts and stress fibres at the margin is consistent with their role, suggested by others, in drawing the bulk of the cell forward. These evaluations are discussed in the context of the form and distribution of contractile proteins in the cell margin. A primary role of the lamellipodia and microspikes in extending the cell margin and forming new adhesions, preparatory to further cytoplasmic movement, is established by this work.
The ultrastructure of prokaryotic-eukaryotic cell junctions
Authors: Tamm Sidney L.
Published: April 2021

Freeze-fracture and thin-section electron microscopy were used to describe the sites of attachment of 2 kinds of ectosymbiotic bacteria to a devescovinid flagellate from termites. In each case, surface specializations in both partners occur at the junctional complexes. Rod bacteria lie in pockets of the eukaryotic membrane which are coated by dense material and contain high densities of intramembrane particles. A double row of closely spaced particles circumscribes the edges of the pockets on the P face. The surface of the rod bacteria which is exposed to the external medium bears a thick glycocalyx and flagella. Fusiform bacteria are attached along ridges of the protozoon surface. Dense material underlies the ridges, and particles are aggregated on both P and E faces of the ridge membrane. The outer layer of the fusiform bacteria is grooved to match the host ridge. The bacterial—devescovinid junctions are considered to serve mainly as attachment sites, and the membrane specializations at the sites of contact are discussed in this respect. Control of junction assembly by the cortical bacteria is suggested by the parallel patterns of junctional replication and bacterial reproduction.
Orientation of calvaria and periodontal ligament cells in vitro by pairs of demineralized dentine particles
Authors: Bellows C. G. , Melcher A. H. , Brunette D. M.
Published: April 2021

Rat calvaria cells (RC cells) and monkey periodontal ligament fibroblasts (MPL cells) were cultured for 4–6 days with demineralized dentine, acid-washed glass particles or untreated glass particles to determine whether the presence of these particles can affect the orientation of the cells. Encapsulation of dentine particles began as early as the first day in culture and occasional cells were attached to, and oriented between adjacent particles. Multilayers of cells formed along the periphery of the dentine particles and the more superficial of these cells projected outwards in a radial fashion. Oriented cell sheets were evident between dentine particles after 3 days in culture. Finally, the cell sheets tore away from the surface of the culture dish to give rise to thick multilayered cellular bridges between dentine particles. The nuclear orientation index (ratio of L/W) for each RC cell lying between 15 randomly selected pairs of each particle type in 4-day cultures was measured along 2 axes; the length represented by the shortest distance between the 2 particles and the width perpendicular to this axis. The nuclear orientation index was 1·52 for cells between dentine, 1·13 between acid-washed glass and 1·06 between untreated glass. Control measurements of cells associated with single particles were 1·06, 1·09 and 1·06 respectively. The frequency of cellular orientation occurring between dentine particles was significantly greater than that occurring between acid-washed glass particles (χ2 > 0·001) which in turn was significantly greater than that for untreated glass particles (χ2 > 0·001). The observations and results suggest that the development and maintenance of the observed cell orientation depends upon development and maintenance in the cell sheet of tensional forces oriented parallel to the axis between the dentine particles, and that this is related directly to the capacity of the cells to attach to the particles.
The effects of fibronectin on the migration of human foreskin fibroblasts and syrian hamster melanoma cells into three-dimensional gels of native collagen fibres
Authors: Schor Seth L. , Schor Ana M. , Bazill George W.
Published: April 2021

The effects of fibronectin on the migration of human, skin fibroblasts and Syrian hamster melanoma cells into 3-dimensional gels of native collagen fibres have been examined. Cell migration into the 3-dimensional gel was measured by plating cells on the gel surface and then determining the percentage of cells within the gel at various times thereafter by direct microscopic examination. We find that fibronectin bound to collagen inhibits the migration of human skin fibrobroblasts and stimulates the migration of melanoma cells into the gel matrix. Fibronectin had no apparent effect on cell adhesion to the collagen gels, proliferation or morphology under the conditions studied.
Phagocytosis by macrophages I. kinetics of adhesion between particles and phagocytes
Authors: Ueda Masamichi J. , Ito Tadanao , Ohnishi Shun-Ichi , Okada T. S.
Published: April 2021

A quantitative method for measuring the initial rate of adhesion of foreign particles to mouse peritoneal macrophages, using protein-coated paraffin oil particles, is described. It was performed to measure the rate of adhesion, which is the first step of phagocytosis, separately from the other phagocytic activities. Kinetic studies showed that the cell-substrate adhesion was a Michaelis-Menten type reaction, which has two rate indices, Km and V. The effects of various reagents on the adhesion rate were analysed. KCN and NaN3 change the rate by affecting V, while the changes in the rate brought about by chlorpromazine and filipin are due to their effect on the Km. Cytochalasin B decreased the adhesion rate, but colchicine did not. The initial rate of adhesion decreased with decreasing temperature. An Arrhenius plot of the initial rate showed a break at 30 °C, and gave an activation enthalpy of 14-8 kcal for the process at the physiological temperature. No characteristic change in membrane fluidity was found at 30 °C using electron spin resonance spectroscopy.
Polypeptide synthesis in cell cycle mutants of fission yeast
Authors: Dickinson D. P.
Published: April 2021

The cell cycle of a growing cell is characterized by 3 main periodic events: DNA synthesis, mitosis and cell division. These events generally lie in a dependent sequence, in which one event cannot occur unless preceding events have occurred. The existence of dependent sequences of events raises the possibility that at least some of the gene products involved in the events are synthesized in a dependent sequence parallel to the observable events. To test this hypothesis, the patterns of polypeptide synthesis were investigated in 2 types of cell cycle mutant of the fission yeast Schizosaccharomyces pombe: temperature-sensitive cell cycle (ts cdc) mutants, which become blocked in cell cycle progress at the restrictive temperature; and wee 1 mutants, which are defective in size control over nuclear division, and which divide at a small size. Cells of mutants and wild-type cells were labelled with [35S]sulphate under conditions designed to maximize any differences between the labelling patterns of wild-type and mutant cell polypeptides. The polypeptides were then separated by O’Farrell z-dimensional gel electrophoresis, and the patterns compared.

Although both types of mutation affect cell cycle control, and cause a considerable alteration in the relative proportions of cellular components, an examination of over 700 polypeptides detected on gels revealed no qualitative differences between wild-type and mutant cell polypeptides. These results suggest that a large majority of the more abundant polypeptides in the growing cell are synthesized independently of cell cycle controls directly related to DNA synthesis and division, and that the synthesis of these polypeptides can occur in the absence of normal progress through the cell cycle. Dependent sequences of gene expression do not appear to make a significant contribution to total polypeptide synthesis during the cell cycle, or to the occurrence of periodic cell cycle events such as mitosis. It is suggested that such cell cycle events may result largely through the reorganization of existing cellular components, rather than by the synthesis of new ones.

An unsuccesful attempt was made to detect the wee 1 gene product on gels by surveying a range of mutants for changes in an individual spot. The limitations of gel electrophoresis for this type of survey, and other cell cycle experiments, are discussed.
Chemotactic reorientation of granulocytes stimulated with micropipettes containing fmet-leu-phe
Authors: Gerisch G. , Keller H. U.
Published: April 2021

Human granulocytes were stimulated by means of a micropipette, with an orifice of about 0.2 μm in diameter, which contained fMet-Leu-Phe at a concentration of 10−5 M. The cells were reorientated by extending lamellipodia towards the source of the attractant, often within less than 10 s. Any part of the granulocyte, from the front to the tip of the tail, could be stimulated to produce new lamellipodia. Usually, but not always, this response occurred at the side of the cell nearest to the micropipette.

Cells stimulated from behind responded in one of the following ways : Cells that maintained their polarity extended new lamellipodia at one side of the leading front and reorientated by moving in a U-tum towards the micropipette. Occasionally, the leading front was split because one part of the front tried to make a left-hand and the other a right-hand turn.Formation of lamellipodia at the leading front was arrested and new lamellipodia were formed at the tail instead, indicating reversal of polarity. The result was an immediate change in the direction of locomotion by about 180°.A combination of the first 2 forms of behaviour was observed occasionally. Transiently, lamellipodia were extended from cell surface areas both close to and distant from the micropipette. These observations show that parts of a cell can respond independently to chemotactic gradients by extending lamellipodia towards the source of the attractant. The phenomenon can easily be explained by assuming that a temporal change of attractant concentration is recognized.
Development of the cell wall inTetraselmis:role of the golgi apparatus and extracellular wall assembly
Authors: Domozych David S. , Stewart Kenneth D. , Mattox Karl R.
Published: April 2021

The green algal flagellate, Tetrasehnis, is a key transition organism in the phylogeny of green algae. It has been proposed that the cell wall of Tetraselmis arose evolutionarily from the fusion of scales and that this event secondarily caused the alteration of some cytoplasmic processes such as mitotic and cytokinetic mechanisms. Ultrastructural and developmental studies of the cell wall were performed with several strains of Tetraselmis. Two major wall types are reported. The wall of type 1 cells consists of a thick inner region covered by a layer of regularly repeating subunits of 26 nm, comparable to the subunits found in the median W2-W6 layer of Chlamy-domonas. The more elaborate type 2 cell wall consists of a thick median wall layer, homologous to the type 1 inner wall, with additional inner and outer strata of hairs, grains and scales. Development of the cell wall begins in the endomembrane system, particularly the Golgi apparatus, where fibrillar tufts and electron-dense droplets are synthesized, modified and transported to the outside. Here, the tufts and droplets are displaced around the protoplast and assemble in several steps to yield the intact wall. Edge-growth assembly of the wall occurs here synchronously with cytoplasmic developments to yield the characteristic anterior flagellar pit. Models explaining various aspects of this development are discussed. When released from the cell, the wall subunits are not completely comparable to stellate scales, but appear to correspond to developmental stages of scales in green flagellates possessing body scales.
Rapid cellular translocation is related to close contacts formed between various cultured cells and their substrata
Authors: Kolega John , Shure Michael S. , Chen Wen-Tien , Young Nevin D.
Published: April 2021

Interference-reflection microscopy combined with time-lapse cinemicrography was used to examine the relationship between cell-to-substratum contact patterns and the speeds of translocation for a variety of cell types. Rapid translocation of amphibian leukocytes (average speed = 9·0 μm/min), amphibian epidermal cells (7μm/min) and teleost epidermal cells (7 μm/min) was found to correlate with patterns of broad grey close contacts. Similar contact patterns were found under freshly seeded (2 h) chick heart fibroblasts (moving 1–3 μm/min), the rapidly advancing (1–5 μm/min) margin of spreading human WI-38 fibroblasts, and isolated MDCK canine epithelial cells (0·5–1·0 μm/min). Conversely, numerous dark streaks of focal contact were found associated with the slow rate of translocation displayed by older cultures (72 h) of chick fibroblasts (< 0·1 μm/min), well-spread WI-38 cells (≤ 0·3 μm/min) and confluent MDCK cells (< 0·01 μm/min). It is concluded that close contacts, but not focal contacts, are associated with rapid cellular translocation, and that the build-up of focal contacts is associated with reduced cellular translocation and maintenance of the spread cell shape.