bluuebunny/crossref_metadata_2025 huggingface dataset:
Contraction waves in lymphocyte locomotion
Authors: Haston Wendy S. , Shields James M.
Published: April 2021

In this paper we propose that the constriction ring, a prominent feature of moving leucocytes, is a major source of locomotive force. Analysis of time-lapse films of lymphocytes in suspension and moving through three-dimensional collagen gels, demonstrated that the constriction ring was the morphological manifestation of a wave of circular contraction that moved antero-posteriorly. In lymphocytes in suspension the wave moved, although the cells could not. Analysis of lymphocytes moving through a collagen gel revealed that the waves remained stationary with respect to the external environment while the cell appeared to move forward through them. Passage of a single equatorial contraction wave resulted in cell lengthening: a shortening of the region posterior to the constriction was observed in cells moving through collagen gels, but not in lymphocytes held in suspension, suggesting that attachment of cells to the collagen network was necessary for longitudinal contraction. Lymphocyte attachment to collagen gels was mediated through the rapid extension of bleb-like structures into the collagen network. Transmission electron microscopy (TEM) failed to demonstrate any organized structure at the constriction ring. NBD-Phallacidin staining of lymphocytes together with TEM demonstrated that F-actin was distributed evenly throughout the length of the cell. Cell polarity was clearly recognizable by the distribution of coated vesicles, microvilli, and all organelles to the rear, and Thy 1-2 to the front, of motile cells, but polarity could be reversed by the passage of a single contraction wave starting at the rear of the cell, without prior redistribution of these structures.
Alterations induced by glucose deprivation and tunicamycin in the kinetic parameters of hexose transport in hybrid cells
Authors: White M. K. , Bramwell M. E. , Harris H.
Published: April 2021

Matched pairs of malignant and non-malignant hybrid cells were compared in their response to glucose deprivation and to tunicamycin. Glucose deprivation induced an increase in the maximum velocity in the malignant cells, but not in the non-malignant cells. The Michaelis constant of hexose uptake was largely unchanged by glucose deprivation except in the case of one melanoma derivative, PG19 G—, which showed a large increase in Michaelis constant when deprived of glucose. Tunicamycin increased the Michaelis constant of hexose uptake in both malignant and non-malignant cell lines. It is therefore possible that the Michaelis constant of hexose uptake is affected by the extent of glycosylation of one or more of the cell membrane glycoproteins
A cell-cycle-phase-specific mutant of amoeba
Authors: Gangopadhyay A. , Chatterjee S.
Published: April 2021

The treatment of Amoeba indica with ethylmethanesulphonate (EMS) at early S, late S and late G2 phases of the cell cycle leads to the production of mini amoeba cells in the G2 period. Among them, only a few of the mini cells that originated from EMS treatment at early S phase have been found to be viable and to give rise to stable clones. These mini amoebae show stable and altered characteristic features in cell size, structure, membrane properties, cell-cycle timing and the patterns of macromolecular syntheses as compared to the parental cells. It is suggested that the mini amoeba cell is a size mutant that has a cell-cycle-phase-specific origin. The finding is discussed in relation to preferential mutagenic action involving the functional state of DNA leading to the production of viable mutant amoebae.
The morphology of the granule cells of the olfactory bulb
Authors: Price J. L , Powell T. P. S
Published: April 2021

The granule cells of the olfactory bulb of the rat have been studied in material prepared by the Golgi-Kopsch method for examination with the light microscope, and in material examined with the electron microscope. With the Golgi method, the granule cells are found to have no process which can be identified as a typical axon, but from the superficial aspect of the somata stout peripheral processes arise and pass into the overlying external plexiform layer, while from the opposite side of the cell body several thinner deep dendrites extend towards the deeper parts of the bulb. Both types of processes, as well as the penkarya, have numerous spine-like appendages. On the distal portions of the peripheral processes in the external plexiform layer the appendages are much larger than on the deeper parts of the cell. The deep dendrites have localized swellings along their length which give them a varicose appearance, appendages often arise from these vancosities. The electron-microscopic features of the granule cells correspond well with the appearance of these cells in material impregnated with the Golgi method. The cell somata are small, with very little cytoplasm, and have a relatively large nucleus. The peripheral processes can be identified passing superficially from the penkarya of the granule cells; at their junction with the cell body their appearance is typically dendritic; all the cytoplasmic organelles found in the cytoplasm extend into these processes and none of the features of the initial segments of axons are found. In the external plexiform layer large spine-like appendages, which have been termed ‘gemmules’, arise from the distal portions of the peripheral processes, and participate in reciprocal synapses with the dendrites of mitral and tufted cells. The deep dendrites are much finer than the peripheral processes, and the vancosities which are seen in Golgi material may also be found with the electron microscope. Spines are found on all parts of the granule cells in the granule cell layer, including the peripheral processes, the penkarya and the deep dendrites. In addition to a spine apparatus, these spines commonly have numerous inclusions, including mitochondria, ribosomes, and vesicles which are the same size and shape as the synaptic vesicles present in the gemmules; no synapses oriented away from the spines have ever been found.
The response of human monocytes to interaction with immobilized immune complexes
Authors: Eccles M. Helen , Glauert Audrey M.
Published: April 2021

The interaction between human peripheral blood monocytes and immobilized immune complexes has been monitored by morphological and biochemical criteria using an established model system previously used with human eosinophils. The model consists of an agar layer containing immune complexes. Monocytes flatten extensively on these layers and make very close contact with the agar surface; cells incubated on control layers, without antibody, are more loosely attached. After 15 min incubation on immobilized immune complexes there is a ‘pulse’ of lysosomal enzyme release from the monocytes and electron micrographs indicate that extracellular secretion occurs. Simultaneously, two proteins with apparent molecular weights of 50000 and 25 000 appear at the cell surface as a specific consequence of the interaction with immune complexes. These newly accessible proteins were detected by lactoperoxidase-catalysed iodination, and the major of the two (labelled M3) has similarities to a protein with an apparent molecular weight of 55 000 of human eosinophils (labelled protein 3), which has been shown to be closely associated with the eosonophil Fc receptor. It will be of interest to establish whether a similar association occurs in monocytes.
Regulation of cell shape in Euglena gracilis : II. the effects of altered extra- and intracellular ca2 + Concentrations and the effect of calmodulin antagonists
Authors: Lonergan Thomas A.
Published: April 2021

When cultures of Euglena gracilis Z., normally grown in medium containing 180μM-Ca2+, are resuspended in Ca2+-free medium cells assume round shapes within 10 min, from which they recover slowly when Ca2+ is returned to the cultures. Cultures grown in 10 μM-Ca2+ do not display the typical circadian rhythm in cell shape even though the photosynthesis and cell division circadian rhythms are unaffected. Elevating intracellular Ca2+ levels by the addition of the Ca2+ ionophore A23187 prevents cells from undergoing the two daily shape changes characteristic of growth-synchronized cultures, but does not alter the ability to maintain the cell shapes found at the time of ionophore addition. When the calmodulin inhibitors trifluoperazine or chlorpromazine are added to cultures, the cells always respond by rounding. Cells are not able to maintain any cell shape other than spherical in the presence of these inhibitors and therefore cannot change shape throughout the daily cycle as is found in the control populations.
Extracellular matrix modulation of endothelial cell shape and motility following injury in vitro
Authors: Young William C. , Herman Ira M.
Published: April 2021

We utilized fluorescence microscopy and affinity-purified antibodies to probe the form and function of cytoplasmic actin in endothelial cells (EC) recovering from injury and grown on extracellular matrices in vitro. Bovine aortic EC were seeded onto glass microscope coverslips that had been coated with either BSA, fibronectin, type I and III (interstitial) collagens, type IV (basement membrane) collagen or gelatin. After EC that had been grown on glass, glass-BSA or extracellular matrix-coated coverslips reached confluence, a 300–400μm zone of cells was mechanically removed to stimulate EC migration and proliferation. Post-injury EC movements were monitored with time-lapse, phase-contrast videomicrography before fixation for actin localization with fluorescence microscopy using affinity-purified antibodies. We found that the number of stress fibres within EC was inversely proportional to the rate of movement; and, the rates of movement for EC grown on glass or glass-BSA were approximately eight times faster than EC grown on gelatin or type IV collagen (X velocity = 0·5μm/min versus 0·06μm/min). EC movements on fibronectin and interstitial collagens were similar (X velocity = 0·2μm/min). These results suggest that extracellular matrix molecules modulate EC stress fibre expression, thereby producing alterations in the cytoskeleton and the resultant EC movements that follow injury in vitro. Moreover, the induction of stress fibres in the presence of basement membrane (type IV) collagen may explain the failure of aortic EC to migrate and repopulate wounded regions of intima during atherogenesis in vivo.
Adult, foetal and transformed fibroblasts display different migratory phenotypes on collagen gels: Evidence for an isoformic transition during foetal development
Authors: Schor S. L. , Schor A. M. , Rushton G. , Smith L.
Published: April 2021

Data are presented indicating that the migration of fibroblasts into three-dimensional collagen gels is affected by cell density. We have defined a ‘cell density migration index’ (CDMI) to express this behavioural response in quantitative terms. The results of a survey of 77 different cell types indicate that the CDMI values expressed by normal adult skin fibroblasts and transformed cell lines fall into two distinct, non-overlapping groups. Measurement of the CDMI therefore provides an additional means of distinguishing between normal and transformed cells and may be used in conjunction with other commonly recognized criteria (e.g. anchorage-independent growth) to assess expression of a transformed phenotype in vitro. It is of interest to note that the CDMI values expressed by foetal cells define a group lying intermediate between normal and transformed cells. Both uncloned and cloned foetal cells have been observed to undergo a stable transition to expression of CDMI values characteristic of adult cells when followed throughout the duration of their in vitro lifespan. In addition to providing a novel means of distinguishing between normal adult and foetal cells, our results suggest that foetal fibroblasts undergo an ‘isoformic’ transition at some point in their developmental history, which is manifest in vitro by the expression of an adult CDMI.
An antigen of Plasmodium yoelii that translocates into the mouse erythrocyte membrane upon entry into the host cell
Authors: Murakami Kenji , Tanabej Kazuyuki
Published: April 2021

Monoclonal antibodies against the rodent malaria parasite, Plasmodium yoelii, have been prepared and characterized by indirect immunofluorescence on acetone-fixed infected mouse erythrocytes. The antibody of clone K2 reacted strongly with late trophozoites and schizonts, whereas it did so weakly and diffusely with ring forms and early trophozoites. Strong fluorescence was confined to granular structures in schizonts and merozoites. Parasites that invaded erythrocytes in vitro lost the strong fluorescence. Instead, immunofluorescence appeared in the membranes of erythrocytes infected in vitro with merozoites. Erythrocytes infected with more than one merozoite had intensified immunofluorescence in their membranes. Staining of the invaded erythrocytes with 4’,6-diamidino-2-phenylindole (DAPI) hydrochloride demonstrated that membranes of all the invaded erythrocytes acquired the P. yoelii antigen. These results suggest that the P. yoelii antigen in merozoites is translocated into erythrocyte membranes upon entry into the host cell. Immunofluorescence continued to appear in membranes of infected erythrocytes throughout the intra-erythrocytic parasite growth. Staining of unfixed infected erythrocytes with the K2 antibody failed to detect the parasite antigen. In contrast, immunofluorescence was present in unfixed membranes of erythrocyte ghosts, which had been spontaneously formed after rupture of schizont-infected erythrocytes by merozoite release. No immunofluorescence appeared in either acetone-fixed or unfixed ghosts of normal erythrocytes. These results suggest the antigenic determinant of the P. yoelii antigen is exposed at the cytoplasmic surface of the infected erythrocyte membrane. Immunoprecipitation has revealed that the K2 antibody recognizes a 160×10’ MRP. yoelii antigen.
Ultrastructural characterization and morphometric analysis of human eosinophil degranulation
Authors: Henderson William R. , Chi Emil Y.
Published: April 2021

Human eosinophil degranulation induced by the calcium ionophore A23187 was examined by transmission and scanning electron microscopy, and morphometric analysis. After incubation with A23187, eosinophil degranulation was characterized by granule movement to the cell periphery and pentalaminar membrane fusion between perigranular and plasma membranes. As adjacent granules fused they became swollen and vesiculated; their contents were released into large cytoplasmic vacuoles, which communicated extracellularly through surface pores. Extracellular release of eosinophil peroxidase without release of lactate dehydrogenase occurred after treatment with the ionophore. Morphometric analysis of the transmission electron micrographs indicated a significant reduction of cytoplasmic granules in the degranulated cells. There was a loss primarily of larger granules and alternatively an increase in the smaller-sized granules (less than 0·1 μm2), suggesting the possibility that exocytosis of mature granules is accompanied by new cytoplasmic granule formation.
Cytoskeletal reorganization and plasma membrane fusion in conjugating Tetrahymena
Authors: Wolfe Jason
Published: April 2021

The conjugation junction of Tetrahymena is the specialized site where plasma membrane fusion occurs between two cells of complementary mating types. The junction is constructed through a series of cooperative interactions and morphogenetic steps. A contact-mediated interaction between free-swimming, sexually mature and mating-competent cells of two complementary mating types induces a morphological transformation of the anterior tips. Cells then join in pairs aligned by the apposition of their modified tips. Thin sections show that the plasma membranes of the tips are separated by ∼500Â of extracellular space, in which some strands of matrix material can be identified. The cytoplasmic face of the membrane is in contact with a junction-specific thick layer of electron-dense material. At hundreds of independent sites in this junction plasma membranes fuse in a limited manner, thereby establishing hundreds of separate membrane-ensheathed cytoplasmic channels that connect the two cells. At the same locations the thick submembrane layer is interrupted. Consequently, the junction appears to be a structure that is perforated with hundreds of pores. This study poses the question of whether the junction’s submembrane layer is, or includes, a skeletal element. Cells were extracted with the non-ionic detergent Triton X-100 under conditions that yield cytoskeletal frameworks (CFs) that maintain the morphological integrity of the cells. The CFs include chromatin and also cortical structures such as microtubule bands, basal bodies, ciliary axonemes, kinetodesmal fibres and fibrillar epiplasm. CFs of conjugant pairs are also paired, indicating that the junction contains a skeletal element that is responsible for integrating the individual CFs into a higher-order complex. At the ultrastructural level the skeletal structure of the junction includes membrane lamina and a submembrane scaffold, residues of the plasma membrane and thick submembrane layer, respectively, both of which are interrupted at the pores. However, the two separate scaffolds are joined at the rims of the pores. This provides a means by which the separate CFs become integrated. On the basis of images of junctional CFs, which show interruptions of the scaffold without concomitant membrane fusion, but where laminae are pressed close together, a specific model of membrane fusion is proposed. According to this model, the submembrane skeletal scaffold regulates membrane fusion by limiting its occurrence, and the extent of its occurrence.
Circadian rhythm of nucleoli in rat superior cervical ganglion neurons: The two types of fibrillar centres and their quantitative relationship with the nucleolar organizing regions
Authors: Pébusque Marie-Josèphe , Vio-Cigna M. , Aldebert Bernard , Seite Raymond
Published: April 2021

A quantitative stereological analysis was undertaken in nucleoli of rat superior cervical ganglion neurons. In this model, two types of fibrillar centres were observed: (1) small-type fibrillar centres were observed during the light span; and (2) a single large-type fibrillar centre occurred during the dark span near the smaller ones. The present data showed that the drastic increase in the mean volume of fibrillar centres during the dark span involved the occurrence and the progressive enlargement of one single large-type fibrillar centre and a marked rise in the number of small-type centres from 18 ± 2 to 74 ± 5 at 1500 h and 0100 h corresponding to light and dark spans, respectively. The total number of these small-type fibrillar centres per nucleolus increased with the total volume whereas their unit volume remained unchanged. This enabled us to establish some relationship with nucleolar organizing regions (NORs).
Actin-regulating activities in cultured bhk cells
Authors: Koffer Anna , Daridan Myra
Published: April 2021

A large proportion (60-85%) of the actin present in lysates of cultured baby hamster kidney (BHK) cells is monomeric at low temperature. All this G-actin is accounted for in the fractions obtained by high-speed centrifugation of the lysate in the presence or absence of non-ionic detergent; 98 (±7)% of it reacts as monomer in the deoxyribonuclease assay. The fractions nevertheless possess actin polymerization nucleating activity, as assayed by the fluorescence of extraneous pyrene-conjugated actin, reflecting the presence of capping proteins and their complexes with oligomeric actin, which dissociate during the deoxyribonuclease assay. Despite the enhanced nucleation, the total proportion of actin polymerized at equilibrium is reduced, relative to that of actin in the absence of cell extract, presumably because of the presence of ‘barbed’-end capping protein(s). With increasing concentrations of the supernatant material, the proportion of polymerized actin was progressively reduced and the presence of inhibitory activity against polymerization became apparent. On addition of micromolar concentrations of free calcium, nucleation by the supernatant fractions is greatly accelerated, but the extent of polymerization undergoes a further reduction, due to the elevated critical monomer concentration resulting from capping. Inhibition of polymerization by the supernatant fraction in the presence of calcium is much greater than by saturating concentrations of cytochalasin E. These observations are most simply interpreted as showing that the cytoplasm additionally contains a ‘pointed’-end capping protein. The plasma membranes were found to have nucleating activity largely residing in the Triton-insoluble fractions.

Actin cross-linking activity was assayed by adding small proportions of either the supernatant or membrane fractions to a large excess of F-actin and analysing the pellet resulting from a low-speed centrifugation. Supernatant fraction, containing Triton-soluble membrane-derived material, possessed much greater cross-linking capacity than the membrane-free supernatant prepared in the absence of detergent. The membrane fractions had practically no cross-linking activity on their own. Nevertheless, a non-ionic detergent extract of the membrane enhanced the cross-linking activity of the supernatant, indicating the participation of more than one species in a cross-linking process.
Effects of dietary fat on the growth of normal, preneoplastic and neoplastic mammary epithelial cells in vivo and in vitro
Authors: Carrington Christine A. , Hosick Howard L.
Published: April 2021

In order to determine: (1) whether there is a growth-regulating interaction between the mammary fat pad and mammary epithelium; (2) whether this interaction could be modified by dietary fats; and (3) whether these effects could be demonstrated in vitro, the following experiments were performed. Virgin Balb/c mice had the left inguinal mammary fat pad cleared of epithelium and were then maintained on one of four fully defined diets. These diets contained the following proportions of fat by weight: 5% or 10% mixed fats; 20% saturated fat plus cholesterol; or 20% polyunsaturated fat. To test for effects in vivo, animals received subcutaneous injections into the cleared fat pad of tumorigenic mammary cells (WAZ-2T(+SA) or WAZ-2T (—SA)) or preneoplastic mammary cells (CL-S1). Dietary fat had little effect on the latent period of tumour formation, but a low-fat diet increased the invasive/metastatic potential of both tumorigenic cell lines. A high-saturated-fat diet inhibited the growth of normal and preneoplastic epithelium in vivo. To test for effects in vitro, CL-S1 cells were co-cultured with explants of cleared mammary fat pad embedded within collagen gels. CL-S1 cells co-cultured with adipose explants obtained from mice fed on a diet containing 20% polyunsaturated fat showed a threefold increase in incorporation of [3H] thymidine into trichloroacetic acid-precipitable material. These results imply that dietary fats may affect the growth of mammary epithelium in two ways: the inhibition of growth caused by the high-saturated-fat diet may be due to systemic effects as it was not apparent in vitro; the increase in growth seen in vitro and caused by a high-polyunsaturated-fat diet is due to a direct interaction between the mammary fat pad and mammary epithelial cells. This interaction may be masked by systemic effects in vivo.
Timing of sulphogalactolipid biosynthesis in the rat testis studied by tissue autoradiography
Authors: Lingwood Clifford A.
Published: April 2021

The testicular synthesis of sulphatoxygalactosylacylalkylglycerol (SGG) has been studied in the rat by autoradiography of frozen tissue sections following in vivo metabolic labelling. The results are consistent with the synthesis of this major mammalian germ-cell glycolipid at the zygotene and early pachytene stages of spermatogenesis. Further synthesis of SGG is prevented by the appearance of an inhibitor of galactolipid sulphotransferase activity at the mid-pachytene stage.
Polymorphous endocytotic organelles in the receptor-mediated endocytosis of gold-labelled α2-macroglobulin complexes by human fibroblasts
Authors: Van Der Schueren B. , Gasser D. , Marynen P. , Van Leuven F. , David G. , Cassiman J.-J. , Van Den Berghe H.
Published: April 2021

The receptor-mediated endocytosis of gold-labelled α2macroglobulin complexes with trypsin or methylamine (α2M-T-Au or α.2M-MA-Au) was studied by electron microscopy in human skin fibroblasts. The gold label was found in coated structures and very small tubules as well as in tubulovesicular structures and in multivesicular bodies/lysosomes. Thick sections (200nm), but especially serial thin sections, clearly showed the polymorphic character of the cellular structures involved in endocytosis. Numerous intercommunications were particularly obvious between the tubulovesicular structures, the larger vesicles and the multivesicular bodies (MVB). Continuities between MVBs and endoplasmic reticulum and interconnections between MVBs were also observed. The specificity of the staining reaction was confirmed by indirect labelling of intracellular α2M by polyclonal and by monoclonal antibodies on ultracryosections. These findings are discussed in relation to observations made on epithelial cells with other ligands.
Protein synthesis and uptake by isolated cecropia oocytes
Authors: Anderson Lucy M.
Published: April 2021

A procedure has been developed for separating the oocytes and follicular epithelium-nurse cell complexes making up the vitellogenic ovarian follicle of the Cecropia moth. Both components remained viable during short-term in vitro incubation in female blood. Isolated epithelial cells were found by autoradiography to incorporate tritiated amino acids and to secrete a fixable, non-dialysable labelled material. Isolated oocytes incubated in a blood medium containing this tritiated, dialysed follicle cell product incorporated it in small cortical yolk bodies, presumably by pinocytosis. Quantitative perchloric acid-precipitation and scintillation counting indicated that the amount of labelled material incorporated by the oocytes increased with time. These results provide direct confirmation of a follicle contribution to the yolk.

Isolated oocytes were also tested for their ability to incorporate labelled amino acids. Fixable label was observed autoradiographically throughout the oocyte cytoplasm, with the greatest concentration in the cortex, but little appeared in the yolk spheres. The amount of perchloric acid-precipitable amino acid in oocytes incubated in female blood increased with time for up to 2 h and then remained constant or decreased slightly. In medium that had been previously conditioned by follicle cells and dialysed, however, incorporation of labelled amino acid continued for at least 4 h. A possible interpretation of this result is that stimulation of pinocytosis by the epithelial cell products causes increased turnover of cell membrane and demands continued synthesis of new proteins.

Labelled female blood proteins were not incorporated into yolk to an appreciable extent by isolated oocytes, even in the presence of follicle cell product. Perhaps extracellular pre-concentration, as occurs in the intact follicle, is necessary for effective accrual of blood proteins. The female blood proteins did become associated with the oocyte cortex, however, and exhibited a higher affinity for the oocyte than male blood proteins. Thus preferential adsorption to the oocyte surface may be a component of the selection process in vitellogenesis.
Shape control in the human red cell
Authors: Backman Lars
Published: April 2021

When the human red cell consumes its ATP, the cell loses its discoid character in favour of a spiculated and eventually a spherical form. This discocyte—echinocyte transformation parallels both degradation of phosphatidylinositol 4,5-bisphosphate and phosphatidic acid but not dephosphorylation of cytoskeletal proteins. Dephosphorylation of both spectrin and band 3 lags behind metabolic crenation.

Exogenous vanadate accelerates both shape changes and lipid dephosphorylation in a parallel manner during metabolic depletion. In contrast to its effect on lipids, vanadate reduces the rate of protein dephosphorylation. These observations strongly support a shape control mechanism in the red cell, based on phosphoinositide metabolism and compatible with a bilayer-couple model.
Freeze-fracture analysis of thylakoid membranes and photosystem I and II enriched fractions from Phormidium laminosum
Authors: Glick Richard E. , Triemer Richard E. , Zilinskas Barbara A.
Published: April 2021

Thylakoid membranes of the thermophilic cyanobacterium Phormidium laminosum have been fractionated into photosystem II and photosystem I particles. These fractions have been characterized by their partial electron transport activities, and biochemical and spectral properties. Exoplasmic fracture face and protoplasmic fracture face particles in the unfractionated thylakoid membranes were shown to correspond in size to particles in freeze-fractured photosystem II and photosystem I fractions, respectively. Differences between the histograms of the thylakoid membrane protoplasmic fracture face particles and the isolated photosystem I particles suggest that in addition to photosystem I complexes some of the particles on the thylakoid protoplasmic fracture face may be related to cytochrome b/f complexes, the hydrophobic component of the coupling factor, or respiratory complexes.
Reactivation of euglenoid movement and flagellar beating in detergent-extracted cells of Astasia longa: Different mechanisms of force generation are involved
Authors: Suzaki T. , Williamson R. E.
Published: April 2021

Detergent-extracted cell models of the euglenoid flagellate, Astasia longa, were obtained that rounded-up on addition of calcium. Treatment with 4% Triton X-100 and Nonidet P-40 removed the flagellar membrane, all membranous structures inside the cell body and the plasma membrane at groove regions of the cell surface. Maximum rounding-up was induced when the concentration of free calcium was raised to ≥10−7M, and ATP strongly enhanced this response. The ionic requirements and sensitivity to vanadate were different from those for the reactivation of flagellar movement. The results suggest that the mechanism of force generation is different from the dynein-based system of the flagellum and that a rise in cytoplasmic free Ca2+ concentration might cause euglenoid movement in vivo. The mechanism of euglenoid movement is discussed in relation to other protozoan motile systems.
Surface contraction of dividing newt eggs induced by lowering the external ionic strength or ph, or by trypsinization
Authors: kubota Tomoyuki
Published: April 2021

As the first cleavage progresses, newt (Cynopus pyrrhogastef) eggs deprived of their vitelline membrane grow to expose the new, unpigmented surface to a saline medium (full-strength Steinberg solution). Further exposure of these eggs to sucrose medium resulted in rapid and extensive contraction of the unpigmented surface. In the sucrose medium the contraction continued until the next cleavage, and eventually the eggs divided into many blastomeres. But partial reversal of the contraction was observed when, after brief treatment with sucrose medium, the eggs were returned to saline medium. This and other experiments indicated that the contraction was due to lowering of the extracellular ionic strength. A similar type of contraction was induced by acidification of the saline medium or by trypsinization. The contractions induced by these treatments did not absolutely require the presence of external Ca2+, had a rapid time course, and were restricted to the unpigmented region, suggesting that they had a common mechanism. Acidification of the egg cytoplasm with CO2 did not result in significant contraction. These findings, together with those of others, suggest that contraction of the unpigmented surface induced by these treatments is due to conformational changes of surface material.
Plasmalemmal vesicles and the effects of sterol-binding agents in rabbit aortic endothelium
Authors: Simons H. L. , Severs N. J.
Published: April 2021

The rims of vesicle openings in capillary endothelium are reported to be highly sensitive to perturbation by the sterol probe filipin when this agent is administered by perfusion at 50 μM concentration in aldehyde fixative for 10 min. If, as supposed, this specific rim response reflects functionally significant aspects of membrane organization at the vesicle–plasmalemma boundary, then it would be expected to be a reproducible and universal feature of endothelial vesicles in general. In the present study, we have investigated in detail the response to filipin of rabbit and rat aortic endothelial plasmalemma. First, the effect of standard filipin treatment (150 μM, 3–20 h) was examined by freeze-fracture. The extensive generalized response observed, taken together with the effects of filipin seen by fluorescence microscopy of stripped aortic endothelial sheets, and the marked corrugation of the plasmalemma observed by freeze-fracture after tomatin treatment, indicate that substantial amounts of cholesterol are present in the membrane. Exposure of rabbit aortic endothelium to 50 μM filipin for 10, 20, 40 and 60 min enabled the progressive appearance of filipin deformations in the plasmalemma to be traced. Even at the very earliest stages of the response, there was no preferential association of filipin deformations with endothelial vesicle rims. Similar experiments in the rat gave the same result. Specific sensitivity of endothelial vesicle rims would, therefore, seem to be either non-universal in occurrence or non-reproducible, and so is unlikely to reflect any membrane property of fundamental significance to endothelial vesicle function.
Stimulation of actin synthesis by cytochalasin d is specific for the isoactins normally expressed in muscle or non-muscle cells
Authors: Tannenbaum Janet , Miranda Armand F.
Published: April 2021

Treatment of human muscle myotube cultures with 2 μM-cytochalasin D (CD) for 6 h stimulated synthesis of both the (muscle-specific) a-actin and the (non-muscle) β and γ-actins usually expressed by these cells. In non-muscle (HEp-2) cell cultures, CD enhanced synthesis of β and γ-actin, but did not induce synthesis of α-actin, which is not normally present in these cells. Thus, synthesis of both muscle and non-muscle actins can be increased by CD, but enhancement of actin synthesis results from increases in the isoactins usually present, rather than induction of new isotypes. Comparison of CD-treated (fused) myotube cultures with (unfused) myoblast cultures indicated that β and γ-actin synthesis was similarly enhanced in both cultures, but that α-actin synthesis was stimulated to a greater extent in the myoblast cultures. Desmin synthesis was also stimulated in the myoblasts but not the myotubes, suggesting that the effect of CD on synthesis of these developmentally regulated cytoskeletal proteins (a-actin, desmin) might be modulated by fusion or the state of differentiation of the muscle cell.
Chemokinetic behaviour of insect haemocytes in vitro
Authors: Takle Garry B. , Lackie Ann M.
Published: April 2021

Time-lapse microphotography was used to film the locomotory behaviour of cockroach haemocytes in vitro, and the cell tracks were analysed for speed and persistence; the percentage mobilization and the diffusion rate of the population were calculated. Haemocytes are either fast locomotor or spread moving cells, or non-motile spread or rounded cells; the first three types are plasmatocytes and their behaviour is interchangeable. Approximately 20% of the cells are motile under control conditions and there is no correlation between orthokinesis and klinokinesis. If activated haemocyte lysate supernatant (HLS), a source of components of the prophenoloxidase enzyme sequence, is added to the cell monolayer, up to 80 % of the cells switch to fast locomotor behaviour, rounding up and moving faster and for longer in straight lines. Neither heat-inactivated HLS nor zymosan supernatant, used to activate HLS, had any effect. If the chemokinins present in activated HLS are also released in vivo on haemocyte activation or during cuticular wounding, then they and the induced changes in haemocyte adhesion could contribute to haemocyte recruitment to sites of infection.
Distribution of the 70K U1 RNA-associated protein during interphase and mitosis: correlation with other U RNP particles and proteins of the nuclear matrix
Authors: Verheijen Ron , Kuijpers Helma , Vooijs Peter , Venrooij Walther Van , Ramaekers Frans
Published: April 2021

Earlier studies suggested that the 70K (70 × 103Mr) polypeptide is a nuclear matrix (associated) protein since it is the only U1 RNP-associated antigen that is not released from the nucleus after treatment of the cell with, successively, detergents, DNase I and/or RNase A and high salt. The possibility that the 70K protein functions in the binding of U1 RNP to the nuclear matrix is now further substantiated by the finding that U1 RNP particles that did or did not contain the 70K protein could be isolated, depending on the method of isolation. When U1 RNP particles were obtained by means of sonic disruption of the nucleus they contained the 70K polypeptide, whereas particles that were isolated by extraction at room temperature and a slightly alkaline pH lacked the 70K protein but contained the intact U1 RNA and the other U1 RNA-associated proteins.

During interphase the localization of the 70K protein is restricted to the nucleus, giving a dotlike distribution pattern with exclusion of the nucleoli. During prophase to late anaphase the protein is dispersed throughout the entire cytoplasm with the exception of the chromatin regions. Immunofluorescence studies, using a monoclonal anti-70K antibody in combination with human autoimmune sera that react with U1 RNA-associated proteins, demonstrate that the 70K protein is localized in those areas of the cell where other U RNP proteins occur, also during mitosis. Topoisomerase I and nuclear lamins, typical nuclear matrix proteins, show completely different distribution patterns in all phases of the cell cycle.

Assembly of the nuclear envelope is attended by the re-formation of the clustered appearance of the 70K antigen. These results suggest that, although associated with the nuclear matrix fraction in interphase cells, the 70K protein remains associated with the U1 RNP particles during cell division.
Microtubules And Cell Wall Development In Differentiating Protophloem Sieve Elements Of Triticum Aestivum L
Authors: Eleftheriou E. P.
Published: April 2021

The densities of microtubules (MTs) along the lateral walls of developing sieve elements in root protophloem of wheat have been investigated by electron microscopy. They increase gradually in the very young sieve elements to reach a maximum just before the initiation of wall thickening. During wall increment MTs remain at high densities (more than 10MTs μm−1), but their number declines abruptly when wall material deposition ceases.

Cell wall thickening is not uniform: broad ridges alternate with narrow depressions, the latter occupied by plasmodesmata. During wall material deposition MTs overlie the thickenings only, being entirely absent from the non-thick-ened areas. The orientation of MTs reflects that of the currently deposited cellulose microfibrils in the cell wall, all being perpendicular to the direction of cell expansion. Numerous vesicles, apparently of Golgi apparatus origin, are encountered amongst the cortical arrays of MTs. Though the least spacing between the contiguous MTs is much smaller than the diameter of even the smallest vesicles, the latter were seen amongst the MTs, indicating that MTs do not prevent the vesicles from passing between them towards the developing area.

All results favour the suggestion that MTs in sieve elements are involved in cell wall pattern development, cellulose microfibril orientation, and presumably in cell elongation.
Laser-induced fusion of mammalian cells and plant protoplasts
Authors: Wiegand Rosemarie , Weber Gerd , Zimmermann Karin , Monajembashi Shamci , Wolfrum Jürgen , Greulich Karl-Otto
Published: April 2021

An ultraviolet-laser microbeam was shown to be suitable for inducing fusion of individually selected plant protoplasts or of B-lymphocytes with myeloma cells. The fusion took place in normal culture medium and the fusogenic condition perturbed the cells only for a fraction of a millisecond. Without manipulating the cell culture except for exposing the cells to laser light, fusion products between preselected individual pairs may be produced.
Clonal origin of chemically induced papillomas: Separate analysis of epidermal and dermal components
Authors: Deamant F. D. , Iannaccone P. M.
Published: April 2021

A fundamental prediction of the hypothesis that critical events in tumour formation are rare is that the tumours develop by clonal expansion. This prediction has been tested by establishing the isozyme content of tumours induced in mosaic animals whose normal tissues contain two distinguishable isozyme activities. The observation that tumours contain activity associated with one or other of the two cell types present in non-neoplastic tissue has been taken to support the contention that the tumours are clonal in origin. Conversely, the presence of both isozyme activities has been taken to mean that the tumours are derived from a large number of cells. There are conflicting reports concerning the clonal origins of chemically induced epidermal tumours. In this report we present evidence that permits a critical resolution of this controversy. The neoplastic epidermal component of the tumours in mosaic animals was separated from the non-neoplastic dermal components. The neoplastic components were derived exclusively from one or other of the cell lineages present within the mosaic, while the dermal non-neoplastic tissue was shown to be derived from both cell lineages. The data support the view that, irrespective of dose or type of carcinogen, the neoplastic portion of a tumour is clonally derived and that analysis of unseparated tumours is confounded by non-neoplastic dermal tissue. The patch size (number of cells in aggregates of like cell type) was established in the target tissue, isolated epidermis. It has been previously held that the epidermal patch of chimeras is larger than that in X-chromosome-linked mosaics. We have established that this is not the case in isolated epidermis of the mouse.
Effect of phorbol myristate acetate and the chemotactic peptide fNLPNTL on shape and movement of human neutrophils
Authors: Roos F. J. , Zimmermann A. , Keller H. U.
Published: April 2021

The results show that the distinct types of shape produced by phorbol myristate acetate (PMA) and by chemotactic peptides (fNLPNTL) are associated with distinct types of neutrophil movement. Whereas the chemotactic peptide can induce front-tail polarity characterized by an expanding front, a contracted tail and preferential unidirectional movements of intracellular organelles, PMA can only elicit non-polar movements characterized by random formation and retraction of projections all over the surface, intracellular movements of organelles being ill-defined and changing in direction. Combined stimulation of human neutrophils with PMA and fNLPNTL results in a suppression of peptide-induced polarity and the formation of non-polar motile cells resembling those stimulated with PMA alone. The results suggest that the diacyl-glycerol-protein kinase C pathway may be instrumental in transducing or modulating signals to the locomotor apparatus of the cell. PMA-treated cells are, however, still capable of developing directional responses when appropriately stimulated. The findings lead to the hypothesis that distinct types of neutrophil movements are preferentially associated with distinct functions.
Isolation of morphologically intact mitochondrial nucleoids from the yeast, Saccharomyces cerevisiae
Authors: Miyakawa Isamu , Sando Nobundo , Kawano ShigeyukI , Nakamura Soichi , Kuroiwa Tsuneyosiii
Published: April 2021

Mitochondrial nucleoids (mt-nucleoids) of the yeast, Saccharomyces cerevisiae, were isolated from spheroplasts of stationary phase cells and their structure and organization were investigated by fluorescence microscopy, electron microscopy, and biochemical techniques. Isolated mt-nucleoids were spherical or ovoid and 0·3–0·6 μm in diameter, and were about the same size and shape as those observed in the cell by the DAPI staining technique.

Measurement of DNA content of mt-nucleoids, using a video-intensified microscope system, after DAPI staining revealed that a mt-nucleoid in spheroplasts from stationary phase cells contains, on average, 3·9 mtDNA molecules and an isolated mt-nucleoid contains, on average, 3·1.

Negatively stained electron micrographs showed that mt-nucleoids consist of particles 20–50 nm in diameter. SDS-polyacrylamide gel electrophoresis of mt-nucleoids detected 20 species of polypeptides in the molecular weight range from 10×103 to 70×103. Acid-urea/SDS two-dimensional electrophoresis of acid extract from mt-nucleoids indicated that a polypeptide of 20×103 is the only major polypeptide with basic property like histones.
Characterization of antibodies as probes for structural and biochemical studies of tektins from ciliary and flagellar microtubules
Authors: Linck R. W. , Goggin M. J. , Norrander J. M. , Steffen W.
Published: April 2021

Rabbit antibodies raised and purified against three tektins, proteins of flagellar doublet microtubules from sea-urchin sperm (Lytechinus pictus and Strongylocentrotus purpuratus), were used to study tektin biochemistry and their structural localization. Doublet microtubules were fractionated into tektin filaments and separated by SDS-PAGE into three major tektin polypeptide bands (Mr = 47, 51 and 55 (× 103)), which were used to immunize rabbits. Antibodies against each tektin (anti-tektins) were affinity-purified and then characterized by two-dimensional isoelectric focusing/SDS-PAGE immunoblotting and by immunofluorescence microscopy. In twodimensional immunoblots of 0·5% Sarkosyl-resistant fractions of flagellar microtubules, the antibody against the 55×103Mr tektin (anti-55) stained one major polypeptide of 55 × 103Mr and pl 6·9, anti-51 stained two polypeptides of 51×103Mr and pl ≈ 6·15, and anti-47 stained one major polypeptide of 47× 103Mr and pl 615. The anti-tektins also stained several minor neighbouring polypeptides, which may be isoelectric variants, novel tektins or unrelated proteins. Furthermore, anti-47 crossreacted with the major 55×103Mr polypeptide. By immunofluorescence microscopy all three anti-tektins stained methanol-fixed echinoderm sperm flagella and embryonic cilia. In addition, anti-47 and anti-55 stained unfixed, demembranated axonemes. Besides staining axonemes, all anti-tektins labelled the basal body region, and anti-51 labelled the sperm head envelope. These results indicate that the tektins are a complex family of proteins that are components of axonemal microtubules and possibly other cytoplasmic and nuclear structures.