bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphological Changes Of The 3T3-L1 Fibroblast Plasma Membrane Upon Differentiation To The Adipocyte Form
Authors: Fan Jing Yu , Carpentier Jean-Louis , Van Obberghen Emmanuel , Grunfeld Carl , Gorden Phillip , Orci Lelio
Published: April 2021

By quantitative evaluation carried out on freeze-fracture replicas, we have investigated the changes in plasma membrane organization as the 3T3-L1 fibroblast phenotype differentiates into the 3T3-L1 adipocyte form. As differentiation takes place there is a dramatic change in overall appearance of the cell as it acquires large lipid-laden vacuoles. On freeze-fracture replicas we find: (1) a ninefold increase in small invaginations as the cell differentiates from the fibroblast to the adipocyte phenotype; (2) virtually no quantitative change in the larger coated invaginations upon differentiation; (3) a greater density of intramembrane particles in the large invaginations as compared to the uninvaginated membrane in both the fibroblast and adipocyte form. This remains relatively constant with differentiation. By contrast, there is a marked increase of intramembrane particles in the undifferentiated membrane as the cell changes from fibroblast to adipocyte.

The functional significance of these changes in plasma membrane organization is unknown, but they significantly correlate with the onset of lipogenesis by the cell.
Microtubule-organizing centres during the cell cycle of 3T3 cells
Authors: Brooks Robert F. , Richmond Frances N.
Published: April 2021

When Swiss 3T3 cells are treated with colcemid for 60 min (0 · 5–2 μ g/ml), although the cytoplasmic network of microtubules is considerably reduced, a significant but variable number of microtubules remain. These residual microtubules appear to converge on a single, usually ciliated, organizing centre. In contrast, on removal of the colcemid, microtubule regrowth takes place from two organizing centres in approximately 50 % of the cells. Surprisingly, whether a cell has one or two organizing centres during recovery does not depend on its position in the cell cycle, though recovery takes place earlier in serum-stimulated cells than in serum-starved quiescent ones. It seems likely that prior to colcemid treatment, cells contain two potential organizing centres only one of which is normally active, the inactive one becoming active after exposure to the drug.
Glycoproteins and glycosaminoglycans of cultured normal human epidermal keratinocytes
Authors: Brown Keith W. , Parkinson E. Kenneth
Published: April 2021

[3H]glucosamine has been used to label metabolically kératinocyte cell-surface glycoconjugates. The major labelled bands identified on sodium dodecyl sulphate/polyacrylamide gels had apparent molecular weights of greater than 250000, and 150000–80000. Most of these components were trypsin-sensitive, indicating that the label was protein-bound. Some of the labelled components were shown to be proteoglycans and the labelled glycosaminoglycans released from them by trypsin were identified as hyaluronic acid (54%), heparan sulphate (33%) and chondroitin sulphate (13%). Specific immunological methods (immunoperoxidase staining and immunoprecipitation) showed that keratinocytes produced fibronectin. Immunoperoxidase staining showed keratinocytes produce only small ‘stitches’ of fibronectin at cell edges; no large fibrils were seen nor any staining over or between cells.
High yields from microcarrier cultures by medium perfusion
Authors: Butler M. , Imamura T. , Thomas J. , Thilly W. G.
Published: April 2021

A culture perfusion system is described for the growth of anchorage-dependent cells on microcarriers. The critical component of this system is a column separator, which removes medium while allowing the microcarriers to remain in the culture. Amino acids and ammonia were analysed during cell growth of the perfusion culture. None of the amino acids was completely utilized. The accumulation of ammonia to 2·3 mM was observed and may be responsible for, or coincident with, events limiting further cell growth. It is suggested that oxygen deprivation and growth inhibitor accumulation, rather than nutrient depletion, are the major factors in limiting even higher cell yields.
Neuronal motility: The ultrastructure of veils and microspikes correlates with their motile activities
Authors: Tosney K. W. , Wessells N. K.
Published: April 2021

We have documented the ultrastructural characteristics that correlate with protrusion, adhesion and retraction of neuronal veils and microspikes, by filming individual neurons of the chick ciliary ganglion and examining the same cells with high-voltage electron microscopy.

We find that new veils invariably contain only a cortical meshwork of filaments and are devoid of microtubules, groups of vesicles and other organelles. At sites of recent veil retraction a cortical meshwork on the substratum side underlies a filament-free space containing vesicle clusters and a complexly folded upper membrane. Areas without veil activity are smooth-surfaced and contain a three-dimensional lattice of filaments. We discuss the implications of these observations for the mechanisms of surface recruitment and retrieval during motile activity.

We also find that the ultrastructure of moving and attached extensions of the cell surface differs dramatically. Unattached microspikes and actively extending veils have an open, criss-cross array of filaments, whereas attached microspikes contain more aligned filaments, which extend as a small bundle into the growth cone. These results suggest that cell surface protrusion is mediated by meshworks of loosely packed filaments. More compact bundles of filaments are probably generated only at adhesion points.
Action Spectrum For Changes In Spindle Fibre Birefringence After Ultraviolet Microbeam Irradiations Of Single Chromosomal Spindle Fibres In Crane-Fly Spermatocytes
Authors: Sillers Peggy J. , Forer Arthur
Published: April 2021

Single chromosomal spindle fibres in Nephrotoma suturalis (crane-fly) spermatocytes in metaphase and anaphase were irradiated with monochromatic ultraviolet light focussed to a 2μm spot. In cells in both metaphase and anaphase either the birefringence of the irradiated spindle fibre was altered in the irradiated region, or there was no change, depending on the dose and wavelength of ultraviolet light used for the irradiation. When there was an area of reduced birefringence (ARB), it moved poleward regardless of whether the associated chromosome moved poleward. When cells were irradiated in early metaphase they remained in metaphase until the ARB reached the pole. In some cells irradiated in late metaphase the chromosomes began anaphase before the ARB reached the pole ; in many such cells anaphase was abnormal in that all six half-bivalents separated at the start of anaphase but none moved polewards.

In all cases the ARB moved poleward at the same speed as subsequent chromosome movement; that is, at about 0·8μm/min.

In cells irradiated in anaphase, spindle fibre birefringence was reduced independently of blockage of chromosome movement. Because birefringence and movement were altered independently there were four classes of results: (1) in some cases there was no effect on the movement of the chromosome associated with the irradiated spindle fibre and no effect on the birefringence of the irradiated spindle fibre. (2) In some cases, primarily with 260 nm wavelength light, there was no effect on the movement of the chromosome associated with the irradiated spindle fibre and there was an effect on the birefringence of the irradiated spindle fibre. (3) In some cases, primarily with 290 nm wavelength light, there was an effect on the movement of the chromosome associated with the irradiated spindle fibre and no effect on the birefringence of the irradiated spindle fibre. (4) In some cases, primarily with 270 nm and 280 nm wavelength light, there was an effect on the movement of the chromosomes associated with the irradiated spindle fibre and there was an effect on the birefringence of the irradiated spindle fibre.

The action spectrum for reducing spindle fibre birefringence in crane-fly spermatocytes had two peaks, one at 260 nm and the other, less sensitive, at 280 nm. For irradiations at 270 nm, 280 nm and 290 nm, five to fifty times more energy was needed to reduce spindle fibre birefringence than to stop chromosome movement, but for irradiations at 260 nm five times less energy was needed to reduce spindle fibre birefringence than to stop chromosome movement. The action spectrum for reducing spindle fibre birefringence is quite different from that for stopping chromosome movement.
Feulgen Banding Of Heterochromatin In Plant Chromosomes
Authors: Marks G. E.
Published: April 2021

Feulgen bands can be obtained at the sites of constitutive heterochromatin in the chromosomes of Anemone blanda, Fritillaria lanceolata and Scilla siberica, simply by means of a short or extended acid hydrolysis. Extended hydrolysis gives positive bands in A. blanda and F. lanceolata and negative bands in S. siberica. Short hydrolysis gives no bands in A. blanda and S. siberica but gives negative bands in F. lanceolata. The kind of Feulgen banding obtained is not correlated with the type of base richness of the heterochromatin DNA; rather, it is probably due to differences in the associated nucleoproteins.
Attachment Of Paramecium To Polystyrene Surfaces : II. Induction Of The Attachment By Hydrophobic Reagents Or Immune Immunoglobulin G
Authors: Kitamura Akio , Steers Edward
Published: April 2021

Mating-reactive cells of Paramecium multimicronucleatum attach to a polystyrene surface (Falcon 1007 culture dishes) irrespective of extracellular ion concentration and swimming velocity. This attachment is induced in cells that are not mating-reactive by treatment with purified immunoglobulin G from antiserum, which blocks cells from mating or from antiserum prepared against the surface-localized immobilization antigens. Treatment with certain hydrophobic reagents such as phenethylamine, benzylamine, amphetamine or phenylethylamine also strongly induces attachment. Similar results are obtained with P. caudatum. Micronuclear activation, which normally occurs in the conjugation process, does not occur, however, in cells that are induced to attach to the polystyrene surface.
X-Ray Microanalysis Of Proximal And Distal Tubule Cells In The Mouse Kidney, And The Influence Of Cadmium On The Concentration Of Natural Intracellular Elements
Authors: Kendall Marion D. , Warley Alice , Nicholson J. K. , Appleton T. C.
Published: April 2021

Quantitative X-ray microanalysis of frozen freeze-dried sections of mouse cortex have been used to determine the concentrations of Na, Mg, P, S, Cl, K, Ca and Cd in normal mice and those subjected to 0·7 μmol of cadmium chloride in two subcutaneous injections. These injections result in tissue levels of approximately 100 mg Cd/kg dry weight (<1 mM) in whole kidney when analysed by atomic absorption spectrometry.

There were distinct and characteristic differences – ‘fingerprints’ – in the elemental composition of both cytoplasm and mitochondria in proximal and distal tubules of normal mice that were disturbed by the cadmium treatment.

The most significant effect of the cadmium injections was a highly significant increase in the sulphur content of the cytoplasm and mitochondria of distal tubules and a loss in concentration of Mg, P, Cl, K, and particularly Na, from the mitochondria. These results are discussed in the light of current concepts of metallothionein induction (metallothionein is a sulphur-rich protein that acts to bind, amongst other metals, cadmium) and the lack of damage observed in the distal tubules.
Serotonin-Binding Glycoprotein Of Rat Platelets
Authors: Tamir H. , Kupsky W. J. , Huang Y. L. , Gershon M. D.
Published: April 2021

Platelets, because of their ability to take up serotonin, are often considered as models of serotonergic neurons. We have purified a glycoprotein from rat platelets that specifically binds serotonin (KD = 10 nM) but not [3H]imipramine (up to 0·2 μM). This protein is distinct from fibronectin. Antiserum raised against this protein was shown to be monospecific by double diffusion, rocket immunoelectrophoresis and immunoreactivity of protein transferred from slab gels to nitrocellulose sheets. We have called this protein serotonectin. Serotonectin-like material was localized by light- and electron-microscopic immunocytochemistry in rat platelets, using the unlabelled peroxidaseantiperoxidase complex bridge technique. All serotonectin immunoreactivity was found to be associated with the plasma membrane but no immunoreactivity was found in the surface connecting system. Washing platelets with Krebs solution removed 75% of the extractable serotonectin, indicating that it is a peripheral protein. Serotonectin was found to be circulating in the plasma, as the ease of its removal from platelet membranes suggests it must do; however, none was found in brain synaptosomes. Serotonectin was found to be synthesized in blood-forming organs (spleen, bone marrow) but not in the liver or the mucosa of the gut. Antibodies to serotonectin (4·5 mg/ml) inhibited the uptake of [3H]serotonin (0·2 μM) by rat platelets but not by synaptosomes. Serotonectin did not bind [3H]imipramine and washing the protein off platelet membranes did not impede the binding of [3H]imipramine to the membranes. Thus an action on serotonectin does not seem to be responsible for the antagonism by tricyclic antidepressants of serotonin uptake. These data suggest that serotonectin is present on the external surface of platelet plasma membranes, that it is excluded from the plasma membrane of the surface connecting system, and that it may be in equilibrium with free material in plasma.
Higher-Order Structure Of Chromatin From Resting Cells : I. Electron Microscopy Of Chromatin From Calf Thymus
Authors: Cavazza B. , Trefiletti V. , Pioli F. , Ricci E. , Patrone E.
Published: April 2021

Extremely large domains of the genome of resting cells (calf thymus) have been visualized in the electron microscope by combining mild extraction procedures with a non-artifactual method of mounting the sample (the phospholipid monolayer technique). The observed chromatin strands, free from distortion, reach contour lengths up to 60μm.

After lysis of the nuclei, four classes of fibres may be identified on the basis of their diameters (30, 24, 18 and 11 nm, respectively). The morphology of giant chromatin strands is strikingly regular; long trains of equally sized, arc-shaped segments are observed, their length being, in many cases, multiples of a fixed value. The inflection points delimiting contiguous segments are often associated with laminar fragments of the nuclear envelope or, less frequently, linked to fibrillar elements. It appears that higher-order structures of chromatin in resting cells conform, to a large extent, to a so called ‘drapery-like’ model, according to which a continuous strand runs between contiguous an-chorage sites placed on the nuclear envelope. Because of the presence of regularly spaced inflection points, this organization is much more ordered than expected.

Spontaneous unwinding of the fibres at low ionic strength, limited nuclease digestion, and relaxation in the presence of ethidium bromide, have been used as probes of the conformation. All these experiments rule out its identification with a single-strand helix. The final ordered state is attained by folding the basic 11 nm strand and by winding up this configuration on itself. This leads to a coiled-coil or ‘rope-like’ model. The 11 nm strand is ‘punctuated’ by sharp kinks. Roughly, it may be assimilated to a chain of semirigid, freely joined elements. As a consequence, local flexibility is greatly enhanced, so allowing the assembly mode described.
Ultrastructural analysis of crystalloid endoplasmic reticulum in ut-1 cells and its disappearance in response to cholesterol
Authors: Anderson Richard G. W. , Orci Lelio , Brown Michael S. , Garcia-Segura Luis M. , Goldstein Joseph L.
Published: April 2021

The crystalloid endoplasmic reticulum (ER) consists of hexagonally packed membrane tubules that contain 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase), an intrinsic membrane protein that catalyses the rate-limiting step in cholesterol synthesis. The crystalloid ER appears in a clone of Chinese hamster ovary cells, designated UT-1, that contain high levels of HMG CoA reductase as a result of growth in the presence of compactin, a competitive inhibitor of the reductase. In the present studies, we have used ultrastructural morphometry to estimate that the crystalloid ER: (1) occupies about 15% of the volume of UT-1 cells; (2) contains 3·4-fold more membrane area than the plasma membrane; and (3) contains less than 700 subunits of HMG CoA reductase per μm2 of membrane surface. The crystalloid ER tubules contain 2000 intramembrane particles per μm2 with a mean diameter of 10·4 nm, as determined by freeze-fracture. The crystalloid ER membranes are low in cholesterol, as indicated by the small number of filipin-cholesterol complexes in freeze-fracture images after treatment with filipin. The addition of cholesterol or related sterols to UT-1 cells promoted a rapid and stepwise disappearance of the crystalloid ER. Initially, the crystalloid ER fragmented into randomly arranged vesicles and tubules. Subsequently, membrane-bound structures disappeared from the cell so that after incubation with cholesterol for 24—72h, the cells appeared completely normal. We found no morphological evidence that autophagic vacuoles participate in the degradation. We conclude: (1) that the crystalloid ER is more extensive than necessary merely to support HMG CoA reductase; and (2) that upon exposure to cholesterol the crystalloid ER is degraded by a process that does not involve autophagy.
Ultrastructure and development of the flagellar apparatus and flagellar motion in the colonial green alga Astrephomene guberna culifera
Authors: Hoops Harold J. , Floyd Gary L.
Published: April 2021

Immediately following embryonic cleavage, the cells of Astrephomene have four equal-sized basal bodies, two of which are connected by a striated distal fibre and two striated proximal fibres. The four microtubular rootlets, which alternate between having 3/1 and 2 members, are arranged cruciately. The two basal bodies that are connected by the striated fibres then extend into flagella, while the two accessory basal bodies are now markedly shorter. At this stage the flagellar apparatus has 180° rotational symmetry and is very similar to the flagellar apparatus of the unicellular Chlamydomonas and related algae. Development proceeds with a number of concurrent events. The basal bodies begin to separate at their proximal ends and become nearly parallel. Each striated proximal fibre detaches at one end from one of the basal bodies. Each half of the flagellar apparatus, which consists of a flagellum and attached basal body, an accessory basal body, two rootlets and a striated fibre (formerly one of the proximal striated fibres), rotates about 90 °, the two halves rotating in opposite directions. An electron-dense strut forms near one two-membered rootlet and grows past both basal bodies. During this time a fine, fibrous component appears between newly developed spade-like structures and associated amorphous material connected to each basal body. The basal bodies continue to separate as the distal fibre stretches and finally detaches from one of them. These processes result in the loss of the 180° rotational symmetry present in previous stages. Although the flagella continue to separate, there is no further reorganization of the components of the flagellar apparatus. In the mature cell of Astrephomene, the two flagella are inserted separately and are parallel. The four microtubular rootlets are no longer arranged cruciately. Three of the rootlets are nearly parallel, while the fourth is approximately perpendicular to the other three. A striated fibre connects each basal body to the underside of the strut. These fibres run in the direction of the effective stroke of the flagella and might be important either in anchoring the basal bodies or in the initiation of flagellar motion. Unlike the case in the unicellular Chlamydomonas, the two flagella beat in the same direction and in parallel planes. The flagella of a given cell may or may not beat in synchrony. The combination of this type of flagellar motion and the parallel, separate flagella appears to be suited to the motion of this colonial organism.
Ultrastructure of the dinoflagellate polykrikos : I. development of the nematocyst–taeniocyst complex and morphology of the site for extrusion
Authors: Westfall Jane A. , Bradbury Phyllis C. , Townsend J. W.
Published: April 2021

Development of the nematocyst-taeniocyst complex in the four-zooid stage of a dinoflagellate, Polykrikos kofoidi, was studied by electron microscopy. We observed the following stages: formation of large spherical bodies in islets of cytoplasm containing extensive rough endoplasmic reticulum and Golgi complexes; differentiation of an anlage of first the nematocyst and then the taeniocyst into a tandem pair; and, maturation of the complex into a nematocyst with operculum and capsule, and a taeniocyst with head, neck and body. In the intermediate stages of dinoflagellate cnidogenesis the structurally elaborate pattern of development differed from that of coelenterate nematocysts but in certain features the mature organelles of both groups were similar. Nematocyst-taeniocyst complexes migrated into chutes on zooids two and four near the junction of the annulus and sulcus at the flagellar bases. The specialized chute was partially lined by thimble-shaped organelles of unknown function. The taeniocyst protruded from the surface in association with a striated fibre whose structure and position were those of a trigger to discharge the two organelles. We found no cytostome in this holozoic colony; the structure of the chute suggested that it might also function as a cytostome.
Limited and unlimited growth of sv40-transformed cells from human diploid mrc-5 fibroblasts
Authors: Huschtscha L. I. , Holliday R.
Published: April 2021

Human foetal lung strain, MRC-5, was treated with simian virus 40 and cultures were obtained that had many of the properties of transformed populations. In 10 experiments, only two produced permanent lines, designated MRC-5V1 and MRC-5V2, which have grown to passage 750 and 650, respectively. In all cases, the SV40-treated cultures acquired many of the features of transformation, including production of T-antigen, loss of contact-inhibition, and ability to grow in low concentrations of serum. The presence or absence of other transformed characteristics, such as altered morphology, abnormal karyotype or ability to grow in soft agar, can be used to distinguish between individual newly infected cultures. However, the cells invariably entered a period of slow growth, or crisis, and in eight experiments the cultures subsequently died without the emergence of a permanent line. The report that late-passage diploid cultures are more easily transformed to permanent lines than young cultures has not been confirmed. MRC-5V1 initially had a sub-diploid chromosome number, but during serial passaging this gradually increased. MRC-5V2, which has a more extreme transformed phenotype than MRC-5V1, had a hyper-diploid chromosome number, which also increased during long-term growth. MRC-5V1 became polymorphic for glucose-6-phosphate dehydrogenase, as judged by the heat-lability and electrophoretic mobility of the enzyme. Fusions between MRC-5V1 and Lesch-Nyhan fibroblasts yielded hybrids with a limited lifespan, and certain sub-lines of MRC-5V1 also slowed down, exhibited characteristic signs of senescence and ceased to grow.
Transitions in Dictyostelium discoideum behaviour: Influence of calcium and fluoride on slug phototaxis and thermotaxis
Authors: Dohrmann Ulrike , Fisher Paul R. , Brüderleln Martina , Williams Keith L.
Published: April 2021

Phototaxis and thermotaxis by slugs of Dictyostelium discoideum show transitions that result in bimodality in phototaxis and temperature-dependent orientation up or down temperature gradients. New steps in the sensory transduction chain for these kinds of behaviour are elucidated from studies using inorganic salts (Ca2+, EGTA, KF) and several mutants. KF enhances bimodality of phototaxis, improves the accuracy of thermotaxis, and affects the transition temperatures from positive to negative thermotaxis. Changing the Ca2+ concentration has effects on both phototaxis and thermotaxis. At low Ca2+ concentrations phototaxis and thermotaxis are enhanced. In the presence of EGTA or high concentrations of Ca2+ phototaxis becomes bimodal, thermotaxis is impaired and spontaneous turning is suppressed. These results obtained by changing Ca2+ concentrations are analogous to those obtained previously with sensory transduction mutations, which coordinately affect phototaxis and thermotaxis.
Manganese-dependent cell - substratum adhesion
Authors: Grinnell Frederick
Published: April 2021

I n the presence of manganese, baby hamster kidney cells attached and spread on substrata without added adhesion factors (e.g., fibronectin, lectins). This Mn-dependent adhesion occurred even when the substratum was coated with proteins, such as albumin, haemoglobin, immunoglobulin or ovalbumin, or a dried collagen film. Under similar conditions, cells without Mn in Mg/Ca-containing medium attached poorly and did not spread. Other divalent cations, including Mg, Ca, Fc, Co and Ni, could not replace Mn. Cell surface sites required for Mn-dependent adhesion were destroyed by brief proteolytic treatment of the cells with trypsin or Pronase under conditions where the fibronectin-receptor was unaffected. Also, addition to the incubations of antibodies that inhibited ligand-mediated cell adhesion (e.g., by fibronectin or lectins) inhibited adhesion of cells in Mn-containing medium and caused rounding of cells previously attached and spread in the presence of Mn. The continuous presence of Mn was required for adhesion. That is, cells that were attached and spread in Mn-containing medium and then switched to Mg/Ca-containing medium (which permitted cytoskeletal function) were found to round up and detach. In marked contrast, cells that were allowed to attach and spread on fibronectin-coated substrata in the presence of Mn did not round up when they were switched to Mg/Ca containing medium. Possible explanations for Mn-dependent cell adhesion are discussed.
In vitro reassembly of basal body components
Authors: Gavin R. H.
Published: April 2021

Singlet microtubules and structures that have the morphology and dimensions of the basal body cartwheel complex self-assemble in extracts derived from Tetrahymena basal bodies.
Pollen-stigma interactions inBrassica oleracea:I. ultrastructure and physiology of the stigmatic papillar cells
Authors: Roberts Ian N. , Harrod Gillian , Dickinson Hugh G.
Published: April 2021

The osmotic potential (Ψπ) of the stigmatic papillar cells of Brassica oleracea is —14·8 bars. In laboratory conditions each cell transpires water at rates within the range from 3 × 10−5 to 5 × 10−5 mm3h−1. A small increase in transpiration rate is detected following cross-(compatible) but not self-(incompatible)pollination. No significant changes in Ψπ occur following pollinations of either compatibility.

Electron microscopy reveals an active papillar cytoplasm apparently secreting proteins into the cell wall via small vesicles. The cuticle is discontinuous and freeze-fracture techniques indicate that channels transverse the cell wall, suggesting a possible pathway for the movement of protein molecules of high molecular weight from the cytoplasm to the stigma surface.

Analysis of electron-microscopic autoradiographs of mature, self-incompatible papillae following pulse-chase experiments with L-[3H]leucine and treatment with cycloheximide shows that protein molecules secreted into the cell wall may return to the cytoplasm at a later stage. The significance of these results is discussed in terms of current models of the pollen·stigma interaction in Brassica.
The presence and location of sporopollenin in fruiting bodies of the cellular slime moulds
Authors: Maeda Yasuo
Published: April 2021

The presence of an acetolysis-resistant polymer (sporopollenin) in the cellular slime moulds is demonstrated. This polymer is located on the stalk sheath of fruiting bodies as a bundle of fine fibrils (4–5 nm diameter). The location and structure of sporopollenin in spores are shown to vary considerably, depending upon the species. In Polysphondylium violaceum spores, sporopollenin is composed of fine spicules (4–5 nm in diameter, 25–5 0 nm long) that cover both the outermost layer of spore wall and the inner surface of the cell membrane. The sporopollenin of Dictyostelium discoideum spores is located preferentially close to the inner surface of the cell membrane, forming a mass of electron-opaque fine granules (4–5 nm in diameter). D. mucoroides spores, however, appear not to possess a tight network of sporopollenin, since they were less resistant to acetolysis than those of the other species. The biological significance of the results is discussed with special reference to fruiting body formation.
Globin synthesis in heterokaryons formed between chick erythrocytes and human k562 cells or rat l6 myoblasts
Authors: Lanfranchl Gerolamo , Linder Stig , Ringertz Nils R.
Published: April 2021

Chick globin synthesis was studied in heterokaryons formed between chick erythrocytes and human K562 erythroleukemia cells or rat L6J1 myoblasts. It was found that chick globin synthesis was activated after fusion of definitive (17 to 19-day) chick erythrocytes obtained from 17 to 19-day embryos with K562 cells. Chick globins appeared to be of the adult βA, α D and β types, whereas no embryonic globin synthesis could be detected.

The pattern and time-course of globin synthesis was investigated after fusion of 4 to 5-day embryonic erythrocytes with rat L6J 1 myoblasts. The level of globin synthesis was high at early time points but then decreased. Globin synthesis, however, was still detectable at 9 days in these heterokaryons. Chick βA, α D and ε-globin chain synthesis was observed both at early and late time points after fusion.
Asymmetric distribution of gap junctions amongst identified photoreceptor axons of Lucilia cuprina (diptera)
Authors: Shaw S. R.
Published: April 2021

The relative number of gap junctions within the ring of axon terminals of identified adult photoreceptors has been counted, in the lamina cartridges of Liucilia cuprina. Terminals are similar in size, but some pairs of terminals make up to four times as many junctions with each other as do other pairs; the frequency of connection varies markedly along the length of the cartridge. Junctions across the cartridge occasionally occur out of the normal sequence, frequently in the upper cartridge between one pair of axons. The distributions suggest that mechanical factors transmitted down from the upper cartridge are responsible for the non-uniformities. There may be indiscriminate competition between terminals at some stage of development for a fixed quota of junctions, the groupings of which have to reach a minimum size to remain viable. Amongst the neurones of the cartridge, great specificity is shown in which cells form gap junctions: only receptors Rl–6 are involved, making junctions only with each other. Within this class Rl·6, however, there is no evidence from the distribution of gap junctions for unique cell labelling, that distinguishes one photoreceptor from another. Connections appear to form indiscriminately, on the basis of proximity. This same generalization holds true for a particular class of chemical feedback synapse. The identity of tight-junction-like structures on the photoreceptor axon membrane is also discussed.
Demonstration Of Lymphocyte Surface Lectins That Recognize Sulphated Polysaccharides
Authors: Parish* Christopher R. , Rylatt Dennis B. , Snowden John M.
Published: April 2021

Cholate extracts of murine lymphocytes were shown to contain haemagglutinating activity against autologous erythrocytes. The species specificity and sugar inhibition pattern of the haemagglutinin closely paralleled the specificity of autorosetting, an interaction that had been shown previously to involve the recognition by lymphocytes of carbohydrate structures on autologous erythrocytes. The probable identity of the haemagglutinin and autorosetting receptors was confirmed by experiments utilizing the unique plasma protein autorosette inhibition factor, which appears to block both interactions by masking carbohydrate acceptor sites on erythrocytes.

Detailed sugar inhibition studies revealed that the haemagglutinin and autorosetting receptors have a high affinity for certain sulphated polysaccharides, such as heparin and dextran sulphate. Since similar sulphated polysaccharides have been shown previously to inhibit lymphocyte recirculation, a possible role for these receptors in lymphocyte homing and recirculation is discussed.
Addition of a mannose-6-phosphatecontaining oligosaccharide alters cellular processing of low density lipoprotein by parental and ldl-receptor-defective chinese hamster ovary cells
Authors: Leichtner A.M. , Krieger M.
Published: April 2021

Low density lipoprotein (LDL) was chemically modified by the addition of ω-(6-phospho)· tetra(αl -3)mannosyl-(αl -2)mannose (M56P), a phosphorylated oligosaccharide containing a terminal mannose 6-phosphate residue. Uptake and degradation of this modified LDL (M56P-LDL) by Chinese hamster ovary (CHO) cells occurred via the lysosomal enzyme (mannose 6-phoβphate) receptor pathway. Cellular processing of M56P-LDL was saturable, specific for the mannose 6-phosphate marker, and occurred with approximately threefold higher affinity than that of native LDL by the LDL receptor pathway. Mannose 6-phoβphate receptor activity, as measured by degradation of M56P-LDL, was ninefold lower than the LDL receptor activity. Degradation of M56P-LDL was more sensitive to inhibition by the lysosomotropic agent chloroquine than was degradation of LDL, suggesting differences in the intracellular processing of mannose 6-phosphatebearing ligands and LDL. Previously isolated CHO cell lines defective in LDL receptor activity resembled parental CHO cells in their ability to process M56P-LDL. The potential use of M56P-LDL in the isolation of cells with pleiotropic mutations affecting receptor-mediated endocytosis is discussed.
Localization of concanavalin a binding carbohydrate in chlamydomonas flagella
Authors: Millikin Blake E. , Weiss Richard L.
Published: April 2021

Chlamydomonas flagella are shown to possess two zones of concanavalin A (ConA) binding carbohydrate. The first zone, distinguished by a requirement for a prolonged labelling period for visualization of fluorescein isothiocyanate (FITC)-ConA fluorescence, is localized in the flagellar coat. The second zone is characterized by a rapid FITC- and [125I]ConA labelling subsequent to disruption of the flagellar membrane, but is unaffected by reagents that act only on the flagellar surface coat. Electron microscopy and ferritin-ConA labelling indicate that this subsurface zone is localized between the flagellar membrane and axoneme in the space that we term the flagelloplasm. These results are used to suggest possible functions for ConA binding glycosyl residues in flagella.
Loss of differentiating nematocytes induced by regeneration and wound healing in Hydra
Authors: Fujisawa Toshitaka , David Charles N.
Published: April 2021

Cell death was observed in the nematocyte differentiation pathway in Hydra during head and foot regeneration. This death occurs throughout the regenerating piece, is transient in nature and is selective for committed stenotele and desmoneme precursors. Proliferating nematoblasts are unaffected. Cell death appears to be caused by release of a toxic factor rather than loss of a hormone required for differentiation, since regenerating pieces released a factor that inactivated differentiating nematocytes, and injured animals that had intact head and foot tissue also lost differentiating nematocytes. The inactivated nematocytes are removed by phagocytosis by epitheliomuscular cells.
Arginine synthesis by hepatomas in vitro: I. The requirements for cell growth in medium containing ornithine in place of arginine and the isolation and characterization of variant hepatomas auxotrophic for arginine
Authors: Goss S. J.
Published: April 2021

Cell growtH in ‘ornitHine-medium’ requires tHe expression of two liver-specific genes, tHose for ornitHine transcarbamoylase (OTC) and carbamoyl pHospHate syntHetase I (CPS-I). CPS-II appears unable to replace CPS-I in tHis system. THe need for ?√-acetylglutamate (to activate CPS-I) can be met, at least in part, by providing it in tHe medium. THe otHer gene products involved in arginine biosyntHesis are probably all ubiquitous (i.e. not tissue-specific). In an attempt to study tHe factors responsible for tHe expression of liver-specific genes, variant Hepatomas are isolated tHat Have lost tHe ability to grow in ornitHine-medium. Two classes of ‘orn -’ variants are identified: unstable variants tHat require dexametHasone for adequate CPS-I production, and ‘stable’ variants tHat Have lost many liver-specific traits. Studies on one stable variant sHow tHat it can revert (tHougH rarely), and tHat it regains its various liver-specific traits in a non-coordinate fasHion.
Resistance of mouse lymphoma l5178yaii cells to alkylation with methylmethane sulphonate resides in a late step of excision repair
Authors: Pearson C. M. , Styles J. A.
Published: April 2021

The mutant mouse lymphoma cell line (L5178YAII), resistant to X-rays, ultraviolet light and alkylating agents, was reinvestigated in an attempt to establish the nature of the mutation. These cells were compared with P388 mouse lymphoma cells, which exhibit normal sensitivity to these mutagens. A series of studies was conducted to compare DNA alkylation and strand breakage with cell survival after exposure of the two cell lines to methylmethane sulphonate.

It was found that neither the degree of alkylation nor the removal of the common alkylation products was correlated with the different sensitivities observed in these cell lines. A correlation was established between cell killing and the production of long-lived strand breaks. P388 cells were found to accumulate twice as many long-lived strand breaks compared to L5178YAII cells, at equal levels of alkylation. This suggested that long-lived strand breaks were the major toxic lesions.

Further experiments indicated that these long-lived strand breaks were produced by a process consistent with excision repair. Evidence is also presented that indicates that the mutation in L5178 YAI I cells that is responsible for their resistance may occur in ligase activity or its associated ADP-ribosyl transferase system.
Circus movements in dissociated cells from two new hybrid frog embryos
Authors: Johnson Kurt E. , Adelman Mark R.
Published: April 2021

Circus movements are a peculiar kind of cell movement, seen in many amphibian cells, that involve the formation of a hyaline protrusion from the cell surface and rotation of this blister around the circumference of the cell. Studies of cells from normal Ranapipiens embryos have shown a close correlation between circus movements in vitro and gastrulation related cell movements in vivo. Cells from two developmentally arrested hybrid embryos (R. pipiens ♀ ×R, sylvatica ♂and R pipiens ♀ × R. catesbiana ♂) are deficient in circus movements to an extent that corresponds to their gastrulation deficiencies. This study reports on the preparation of two new hybrids (R. pipiens ♀ × R. temporaria ♂ (temp) and R. pipiens ♀ × R. clamitans ♂ (clam)). Cells from temp embryos show some circus movements but the proportion of cells displaying such movements does not increase with increasing developmental age to the same extent as is seen in cells from normal embryos. Cells from clam embryos show very few circus movements at any developmental age. These aberrations in the onset and extent of circus movements are discussed in relation to characteristic morphogenetic events that occur in normal embryos and in these two new arrested hybrid embryos.
Altered labelling of the cell surface and intracellular organelles with [3H]Mannose in enucleated amoebae
Authors: Flickinger Charles J.
Published: April 2021

The production, transport, and disposition of material labelled with [3H]mannose were studied in microsurgically enucleated and control amoebae. Cells were injected with the precursor and samples were prepared for electron-microscope radioautography at intervals, up to 24 h later. Control cells showed heavy labelling of the rough endoplasmic reticulum and the Golgi apparatus at early intervals after injection. Later, labelling of groups of small vesicles increased, and the percentage of grains over the cell surface peaked 12 h after administration of the precursor. Two major changes were detected in enucleate amoebae. First, the kinetics of labelling of cell organelles with [3H]mannose were altered in the absence of the nucleus. The Golgi apparatus and the cell surface both displayed maximal labelling at later intervals in enucleates, and the percentage of grains over the rough endoplasmic reticulum varied less with time in enucleated than in control cells. Second, the distribution of radioactivity was altered. A greater percentage of grains was associated with lysosomes in enucleates than in control cells. The change in the kinetics of labelling of the endoplasmic reticulum, Golgi apparatus and cell surface indicates that intracellular transport of surface material was slower in the absence of the nucleus. It is suggested that this is related to the decreased motility of enucleate cells.
Post-pollination callose development in ovules of Rhododendron and Ledum (Ericaceae): Zygote special wall
Authors: Williams E. G. , Knox R. B. , Kaul V. , Rouse J. L.
Published: April 2021

In Rhododendron spp. and Ledum groenlandicum a callose wall is laid down around the zygote in the first 2 days after fertilization. The periodic acid/Schiff-positive, aniline blue-fluorescence-positive callosic wall is initiated adjacent to the degenerating synergid, extends to cover the entire zygote surface, and remains visible during the initiation of embryogeny as the zygote elongates before the first proembryonal division. Unfertilized ovules show eventual callose deposition in the ovule wall cells during senescence in undeveloped abscising pistils, but show no development of callose within the embryo sac. Possible roles of a zygote special callose wall are discussed.
Ultrastructural changes during formation and germination of microcysts in Polysphondylium pallidum, a cellular slime mould
Authors: Hohl H.R. , Miura-Santo L. Y. , Cotter D. A.
Published: April 2021

Ultrastructural changes during encystation of Polysphondylium palltdum, a cellular slime mould, include an increase in fibnllar material in the cytoplasmic matrix, the formation of cytoplasms microprojections at the cell periphery and the occurrence of tiny vesicles and some larger vacuoles near the cell periphery. The cyst wall appears first as a fluffy, loose network of fibrils. In the mature cyst it consists of a dense inner and a somewhat looser outer layer. It contains inclusions of apparently cytoplasmic origin. Electron-dense material lines the cell periphery beneath the plasma membrane. Excystment of the myxamoeba is accompanied by a swelling of aggregated vacuoles and polyvesicular bodies, the disappearance of the peripheral cytoplasmic lining, and a general loosening of the wall texture. For a limited period the cisternae of the rough endoplasmic reticulum appear highly dilated. The loosened wall eventually breaks and the myxamoeba emerges by extending pseudopodia through the rupture, leaving the entire cyst wall behind.
Kinetochore ultrastructure in vincristine-treated mammalian cells
Authors: Journey L.J. , Whaley Audrey
Published: April 2021

The ultrastructure of chromosomes from tissue culture cells blocked in division with vincristine sulphate or colchicine was examined. Kinetochores had a distinctive morphology consisting of trilaminar dense plates closely applied to the chromosomes. In longitudinal sections, kinetochores appeared as separate plates attached to opposite sides of the chromosomes. In transverse sections of some prometaphase chromosomes, however, the kinetochore resembled an incomplete ring-like structure encircling the chromatid pair. These observations indicate that sister kinetochores may be continuous during early stages of their formation.
X-ray diffraction and electron-microscope studies of the brush border membrane of guinea pig intestinal epithelial cells
Authors: Limbrick A. R. , Finean J. B.
Published: April 2021

Low-angle X-ray diffraction patterns have been obtained from condensed systems of brush border membranes which contain up to 30 % water and also from hydrated samples of the lipid extracts of the membranes. The diffraction bands obtained from the hydrated membranes were orders (up to n = 8) of a lamellar repeating unit of about 30 nm which included 2 membrane units. By referring to electron micrographs of these condensed membrane preparations, an electron density profile of the brush border membrane has been evaluated, and its significance in relation to the molecular organization of the membrane is discussed.
Mutations induced in amoeba proteus by the carcinogen N-methyl-N-nitrosourethane
Authors: Ord M. J.
Published: April 2021

Mutations have been induced in single amoebae by treatment with the powerful mutagen, N-methyI-N-nitrosourethane. Three mutants, which differ visibly from the parent strain to the extent that individual amoebae are recognizable and change of characteristics from normal to mutant or mutant to normal can be followed in single cells, are described. These mutant strains have been cultured in the laboratory, using Tetrahymena feeding, without loss of mutant characteristics for over 2 years, undergoing some 100 or more cell cycles. Hybrids made between mutants and the parent strain, using the nuclear transfer technique, are viable and stable. They showed that in all cases crosses between normal and mutant amoebae retained the characteristics of the mutant only if the mutant nucleus was present. Though amoebae from 2 of the mutant strains may revert to normal form with increase in temperature or change to a wheat culturing technique, these ‘apparent normal’ amoebae resume the mutant form on a return to the temperature and feeding conditions normally used.

The interaction between mutant and control amoebae was observed in heterokaryons over periods of up to 6 weeks by cutting off pieces of the heterokaryon cytoplasm at regular intervals to prevent division while allowing growth. In general the presence of a control nucleus led to the development of normal characteristics whether the heterologous nuclei were contained in control or mutant cytoplasm. No antagonistic action occurred between mutant and control nuclei when sharing the same cytoplasm. Study of the clones formed by the offspring of heterokaryon divisions showed the mutant and control nuclei unaltered by long periods of close contact. These experiments indicate the chromatin as the site of action of the mutagen. A possible mode of action of the mutagen in amoebae, relating to the functional state of the DNA, is suggested.