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At least 19 recordsLinked to original sources
PubMed1977

Pseudopodia formation by neurosecretory granules.

Ultrastrucal studies of the mouse neurohypophysis, under various experimental conditions, revealed a number of neurosecretory granules (NSG) bearing single pseudopodia-like protrusions. Some NSG adhered to the axolemma via pseudopodia; other NSG, distant from the axolemma, budded electron lucent microvesicles from the tip of the pseudopod. Pseudopodia counts were made on electron micrographs, and calculated as a percentage of the NSG population. In neural lobes from intact mice, small numbers of pseudopodia were observed (0.3%); the count increased significantly after injections of large doses of horseradish peroxidase (HRP) (9.4--14.5%); hypertonic saline augmented the count, as did histamine. In vitro incubation experiments with isolated neural lobes in Krebs Ringer revealed concomitant pseudopodia formation and elevated vasopressin release (measured by antidiuretic bioassay) in the presence of HRP and di-butyryl cyclic AMP respectively. Histamine and excess potassium also increased hormone secretion, but did not induce pseudopodia formation in vitro; pseudopodia were observed neither in controls, nor in the presence of ineffective secretagogues. It is suggested that the pseudopod may represent the active site on the granule membrane. Different ultrastructural images of granule release suggest that several modes of hormone release may be operative in the neurohypophysis. The role of HRP in pseudopodia formation and vasopressin release is enigmatic.

Animals↗
PubMed1977

Evidence for contractile protein translocation in macrophage spreading, phagocytosis, and phagolysosome formation.

Macrophage pseudopodia that surround objects during phagocytosis contain a meshwork of actin filaments and exclude organelles. Between these pseudopodia at the base of developing phagosomes, the organelle exclusion ceases, and lysosomes enter the cell periphery to fuse with the phagosomes. Macrophages also extend hyaline pseudopodia on the surface of nylon wool fibers and secrete lysosomal enzymes into the extracellular medium instead of into phagosomes. To analyze biochemically these concurrent alterations in cytoplasmic architecture, we allowed rabbit lung macrophages to spread on nylon wool fibers and then subjected the adherent cells to shear. This procedure caused the selective release of beta-glucoronidase into the extracellular medium and yielded two fractions, cell bodies and isolated pseudopod blebs resembling podosomes, which are plasma-lemma-bounded sacs of cortical cytoplasm. Cytoplasmic extracts of the cell bodies eluted from nylon fibers contained two-thirds less actin-binding protein and myosin, and approximately 20 percent less actin and two-thirds of the other two proteins were accounted for in podosomes. The alterations in protein composition correlated with assays of myosin-associated EDTA-activated adenosine triphosphatase activity, and with a diminution in the capacity of extracts of nylon wool fiber-treated cell bodies to gel, a property dependent on the interaction between actin-binding protein and F-actin. However, the capacity of the remaining actin in cell bodies to polymerize did not change. We propose that actin-binding protein and myosin are concentrated in the cell cortex and particularly in pseudopodia where prominent gelation and syneresis of actin occur. Actin in the regions from which actin-binding protein and myosin are displaced disaggregates without depolymerizing, permitting lysosomes to gain access to the plasmalemma. Translocation of contractile proteins could therefore account for the concomitant differences in organelle exclusion that characterize phagocytosis.

Actins↗
PubMed1979

The contractile system of blood platelets and its function.

The various manifestations of platelet activation are derived from a reorganization of components of the contractile and microtubular systems. The controversial initial stages of excitation-contraction coupling in platelets lead to the release of calcium from the dense tubular system, the morphological counterpart of the muscle sarcotubular closed vesicles. Calcium triggers the actin-myosin interaction and the developing force, possibly together with a local increase of the cation concentration, may cause the collapse of the microtubular ring and its reappearance in the forming long pseudopodia. Actin-myosin interaction is modulated by several factors among which tropomyosin-troponin, responsible for the calcium-sensitivity of contractile processes, and phosphorylation of one of the myosin light chains. Platelet actin is anchored to the membrane and its sliding towards the short myosin filaments may form the basis for platelet shape change. Platelet alpha-actinin and actin-binding protein are able to aggregate actin into an impressive gel. Therefore, the contractile proteins seem to have a double role in controlling the consistency of the cytoplasmic gel on the one hand, and the contractile manifestations related to motility on the other hand. One of the most important features of the 'contracted' platelet is the rigidity of the pseudopodia brought about by the 'gelification' of actin filaments and the presence of microtubules. A new model for clot contraction is proposed, based on the rigidity of the long spiky pseudopodia and on the motile properties of platelets. While migrating towards each other, the interlocking pseudopodia from different platelets adhere to the polymerizing fibrin, compressing the fibrin nets in their pathway. Since the anchoring of contractile fibers to membranes is crucial for the platelet contractile manifestations, the integrity of the membrane structure should be considered in the study of pathological aspects of platelet function.

Actins↗
PubMed1978

Scanning electron microscopy of cells isolated from amphibian early embryos.

Cells have been dissociated from Xenopus and Ambystoma late blastulae, allowed to adhere to glass coverslips, and studied by scanning electron microscopy. Xenopus ectoderm cells initially show filopodia; later larger single pseudopodia are formed. Ambystoma ectoderm cells show fewer filopodia than Xenopus ectoderm, but later form pseudopodia. Ectoderm cells of both Xenopus and Ambystoma show links between adjacent cells. Xenopus endoderm cells do not show filopodia initially, but later show large pseudopodia.

Ambystoma↗
PubMed1978

Surface topography of isolated gastrula ectoderm of Triturus vulgaris.

The surface topography of the outer cell layer of the two-layered gastrula ectoderm of Triturus vulgaris resembles that of the other amphibians: the cells are tightly packed and devoid of pseudopodia. The cells of the inner layer are spherical and interconnected with pseudopodia of various lengths. After excision of the ectoderm the peripheral cells of the outer layer elongate perpendicularly to the edge of the explant, while the number of pseudopodia on the inner layer greatly increases. The results show that the curling-up of the explant and formation of a sphere results from locomotor activity of the cells in both layers.

Animals↗
PubMed1979

Pinocytosis and locomotion of amoebae: XII. Dynamics and motive force generation during induced pinocytosis in A. proteus.

The mechanism of induced pinocytosis was investigated in Amoeba proteus by light and electron microscopy. The application of nine different inducing substances revealed that pinocytotic channel formation, elongation, vesiculation, shortening and disappearance are the result of the successive or simultaneous action of both traction and pressure forces, which are produced by the contractile activity of a plasma membrane-associated layer of filaments ranging from a few hundred nm to several micrometer in thickness. The initial phase of channel formation is caused by traction forces according to the membrane flow concept, whereas channel elongation and vesiculation mainly result from pressure forces in conjunction with the extrusion of small hyaline pseudopodia. Shortening and disappearance of the pinocytotic channels are brought about by local contractions of the cortical filament layer in the basal region of the hyaline pseudopodia. Experiments using latex beads as marker particles together with inducing substances show that a rapid membrane turnover duirng pinocytosis can be excluded, and that the plasma membrane slides as an entire structure over the underlying cytoplasm.

Amoeba↗
PubMed1979

Ultrastructural observations on the erythrocytes and thrombocytes of the tuatara, Sphenodon punctatus (Gray).

The erythrocytes of Sphenodon punctatus (Gray) are nucleated, ellipsoidal and flattened, and contain 55--65 microtubules in their marginal band. The thrombocytes are also flattened, ellipsoidal, nucleated cells and in electron-microscopic preparations occurred in aggregrates. The thrombocytes appeared to be 'activated' and possessed many pseudopodia which were devoid of organelles. The latter were concentrated in the perinuclear region and were encircled by a ring of microtubules. The organelles included ribosomes, mitochondria, membrane--bound dense material and numerous actin-like microfilaments. Cytoplasmic vacuoles contained a moderately dense, filamentous material and/or spheroidal electron-dense inclusions, beta-glycogen particles were scattered in the general cytoplasm and were most concentrated in the pseudopodia. The erythrocytes and thrombocytes of S. punctatus are compared with those in other vertebrates.

Animals↗
PubMed1979

pH-induced platelet ultrastructural alterations. A possible mechanism for impaired platelet aggregation.

After the observation that lavages with alkaline solutions exert a beneficial effect on the bleeding tendency and increase platelet aggregation in patients with intragastric hemorrhage, studies were undertaken to find a relationship between changes of pH and platelet morphology. Transmission and scanning electron microscopy showed that at a pH lower than 7.4, normal human platelets change their internal structure as well as their shape, becoming spheres deprived of pseudopodia. On the other hand, a pH higher than 7.4 induces transformation of platelet internal organelles similar to that caused by thrombin. At an alkaline pH, the platelets develop multiple pseudopodia that facilitate their attachment to each other. These findings may explain the increased platelet aggregation in alkaline medium demonstrated in one of our previous works.

Blood Platelets↗
PubMed1979

Surface morphology of macrophages in the regressing corpus luteum, as revealed by scanning electron microscopy.

Activated macrophages phagocytize moribund luteal cells and thus play a central role in the postpartum regression of corpora lutea in guinea pigs (Paavola, '79). When viewed by transmission electron microscopy (TEM), these luteal macrophages exhibit many surface protrusions. To characterize more fully the nature and extent of these evaginations, as well as to gain further understanding of phagocytes in their natural surroundings, luteal macrophages were studied in situ by scanning electron microscopy of regressing corpora lutea. Correlated TEM was carried out to confirm the identity of the various cell types. Even in low power scanning electron micrographs, macrophages are consipicuous, and can be readily distinguished from luteal cells by their surface topography. Luteal cell surfaces bear low ridge-like folds and sparse microvilli. In contrast, macrophages characteristically exhibit highly developed surface projections, the most common of which are knob-like or clubbed processes of varying size and shape. Other distinctive surface modifications displayed by luteal macrophages include long, slender filopodia, and well developed pseudopodia. These processes generally have an uneven distribution over the cell; thus, luteal macrophages may appear polarized with regard to surface activity. Both filopodia and pseudopodia occur in close contact with luteal cell surfaces. In addition, occasional luteal macrophages have surfaces that are covered with large, crater-like depressions. The phagocytosis of cells and cellular debris by macrophages was also observed. In summary, the highly pleomorphic surface activity of luteal macrophages appears to be correlated with their role in the removal of senescent luteal cells.

Animals↗
PubMed1979

Endocytic activity of subependymal microglial cells in the toad brain: a cytochemical study of peroxidase uptake.

A population of microglial cells that rapidly incorporate extracellular material introduced into the ventricular system has been identified just beneath the ependyma of all four cerebral ventricles in the toad (Bufo marinus). In untreated tissue these cells appear to be scattered, possess few processes and have an elongate shape with their long axes lying parallel to the ventricular surface. Their most distinctive ultrastructural features are nuclei containing clumps of chromatin, cytoplasmic dense bodies and single strands of granular endoplasmic reticulum. When horseradish peroxidase (HRP) is perfused through the ventricular system and the tissue processed using the DAB cytochemical method, the cells change shape and incorporate HRP into cytoplasmic structures. Even after very short perfusion periods (2-5 minutes) cells become rounded, the surface is ruffled and pseudopodia develop that contain characteristic flocculent material. Reaction product for HRP is contained in plain and coated vesicles, tubules, vacuoles and long structures composed of two closely apposed membranes. At these early times, relatively few multivesicular bodies and dense bodies contain reaction product, but when the cells are viewed at longer time periods after the ventricular perfusion of HRP an increasing proportion of the multivesicular bodies and dense bodies contain reaction product. By 320 minutes reaction product is found almost exclusively in these two organelles. In addition, many pseudopodia containing dense bodies with peroxidase activity are found in the neurophile; some, but not all, can be traced from the subependymal microglial cells. The cell bodies have resumed their flattened shape. When compared to the subependymal microglial cells, other brain cells--oligodendrocytes, astrocytes, ependymal cells and neurons--contain relatively little reaction product at short time intervals; only by 320 minutes are moderate amounts of HRP present. Because of the position of the microglial cells and their ingestive capacity, it is suggested that they function to protect the brain from foreign substances entering from the CSF.

Animals↗
PubMed1977

On the nurse cell and the spermatozeugma in Littorina sitkana.

Nurse cells develop from diploid cells in the testis. Each cell undergoes a reduction division which leaves the nucleus with half the volume of a normal diploid cell. They send out pseudopodia which form desmosome-like junctions with developing spermatids. The nurse cells detach from the testicular wall, their nuclei degenerate and secretion droplets form in the cytoplasm. The pseudopodia are drawn in as the cytoplasmic secretions swell and the nurse cell becomes spherical. The eupyrene sperm become grouped unilaterally and at this stage are attached to the nurse cell by only the tips of their acrosomes. At maturity the nurse cells with their clumps of attached eupyrene sperm (spermatozeugmata) are released from the testis via ducts into the seminal vesicles,where they are stored prior to copulation. Nurse cells serve similar functions to those of apyrene sperm which are common among the Molluscs. We believe that the nurse cell and apyrene sperm are homologous.

Acrosome↗
PubMed2025

Invadopodia in cancer metastasis: dynamics, regulation, and targeted therapies.

Pseudopodia and invadopodia are dynamic, actin-rich membrane structures extending from the cell surface. While pseudopodia are found in various cell types, invadopodia are exclusive to tumor cells and play a key role in cancer progression. These specialized structures enable tumor cells to degrade the extracellular matrix, breach tissue barriers, and invade surrounding tissues and blood vessels, thus facilitating metastasis. Extensive research has elucidated the distinct structure of invadopodia, the signaling pathways driving their formation, and their interaction with the tumor microenvironment. Integrin- and Src kinase-mediated signaling pathways regulate invadopodia dynamics. This review explores the mechanisms underlying invadopodia stabilization and highlights recent insights into their regulation by the tumor microenvironment. Particular emphasis is placed on the role of cell surface signaling in modulating invadopodia activity and the intracellular targeting of matrix metalloproteinases (MMPs) in enhancing invasive potential. A deeper understanding of invadopodia-driven cancer cell migration and metastasis provides valuable implications for therapeutic development. These findings support the potential for receptor-mediated and molecularly targeted therapies to inhibit tumor metastasis, improve clinical outcomes, and enhance the efficacy of existing cancer treatments.

Humans↗
PubMed1978

Cellular morphology and architecture during early morphogenesis of the ascidian egg: an SEM study.

1. Cellular morphology and architecture during early morphogenesis of the ascidian embryo were examined by SEM. 2. The outer surface of the embryo was essentially smooth. The blastocoel could be seen in the dissected blastula. On the cell surface bordering the blastocoel, numerous pseudopodia extended from cells onto adjacent cells. These pseudopodia were suggested to contribute to cell-to-cell adhesion. 3. Before the initiation of gastrulation, a layer of the cells of the animal (ventral) hemisphere and that of the cells of the vegetal (dorsal) hemisphere adhered closely together. The blastocoel could no longer be observed. 4. The gastrulation began during the seventh cleavage. The gastrocoel was formed by a folding of the two layers of the cells. Examinations of the dissected gastrulae suggested two cooperative forces for the gastrulation: first, the epibolic or enfolding movement of the ventral ectoderm cells and secondly, the change in shape of the constituent cells. 5. The neural tube formation progressed in a similar fashion to that of vertebrates.

Animals↗
PubMed1978

Induction of some features of glial differentiation in primary cultures of human gliomas by treatment with dibutyrl cyclic AMP.

Explants from 18 gliomas were cultured for periods up to 7 weeks and studied by light microscopy scanning and transmission electron microscopy. Well-differentiated tumor tissue gave rise to early outgrowths of stellate cells showing process orientation. Poorly-differentiated tissue produced a more haphazard out-growth of pleomorphic cells with few processes and flattened pseudopodia. Mean circadian cell displacement was several times greater in poorly-differentiated cells, but was significantly and reversibly reduced by treatment and dibutyryl cAMP (5 X 10(-4)M) for 48 h. Reduction in motility was directly correlated with a change in cell morphology to a more stellate form. Well-differentiated cells had a smooth surface with ruffling restricted to the ends of processes and highly orientated glial filament and microfilament bundles. The poorly-differentiated cell surface had a microvillous, blebbed appearance and ruffling regularly occurred around the edge of the cytoplasm. Glial filaments and microfilaments were fewer and less well orientated in the poorly-differentiated cells; sites of adhesion to the substratum were fewer than in well-differentiated cells. Treatment of malignant cultures with dibutyryl cAMP resulted in smoothing of the cell surface, retraction of processes into thin pseudopodia and the appearance of microfilament bundles within the cells. These features marked the apparent cyto-differentiation. However, there was a loss of attachment, disappearance of microtubules and loss of glial filaments in the cytoplasm which was not compatible with differentiation. Intracellular recordings of membrane potentials gave a significantly higher mean value for well-differentiated cells. The mean membrane potential and input resistance of poorly-differentiated cells was unchanged by the addition of dibutyryl cAMP. The results of this study suggest that some, but not all, features of mature glia are restored in malignant tumour cells by cAMP treatment.

Brain Neoplasms↗
PubMed1979

The use and limitation of labeled staphylococcal protein A for study of antineutrophil antibodies.

Antineutrophil antibodies can be detected following their attachment to neutrophils by employing labeled staphylococcal protein A (SPA). Radiolabeled SPA provides a sensitive means for identifying the presence of IgG restricted to subclasses IgG1, IgG2, and IgG4 that will specifically bind to neutrophils and that are found in the serum of patients with isoimmune and autoimmune neutropenia. However, SPA bound to the Fc region of IgG does not interfere with the attachment of IgG to the Fc domain of the neutrophil. Fluorescein-labeled SPA, in turn is useful in monitoring the functional consequences of antibody attachment to the surface of polymorphonuclear leukocytes (PMN). Both heterologous and isoimmune antisera induced lateral movement of surface antigens into polar-capped pseudopodia. The formation of such pseudopodia may facilitate leukoagglutination and the subsequent removal of sensitized cells from the circulation.

Animals↗
PubMed1977

Mode of locomotion of Schwann cells migrating in vivo.

The manner of locomotion of Schwann cells during normal development was studied by means of repeated observations and photomicrographs of individual cells at closely spaced time intervals and focal levels. In developing tadpole peripheral nerves, Schwann cells move sporadically with brief periods of rapid translation of the whole cell interspersed with longer intervals when the cell shows little or no overall movement. Highest rates of locomotion averaged 5 micrometer/minute with a duration of no greater than four to six minutes. Net rates of speed measured over at least 20 minutes were always considerably lower, with the average being 1.9 micrometer/minute. Rapid locomotion involves protrusion and growth of several pseudopodia, while the cell body remains in place, followed by attachment of these processes to an axonal surface, and finally detachment of the trailing portions of the cell as the entire cell hitches forward, "inchworm-style".

Animals↗
PubMed1977

Extracellular matrix fibrils and cell contacts in the chick embryo. Possible roles in orientation of cell migration and axon extension.

The migration of neural crest and sclerotome cells and the extension of ventral root axons in chick embryos at stages 16-20 were studied by light microscopy as well as scanning and transmission electron microscopy at the leg bud level of fixed specimens. Extensive cellular movements take place in association with an extracellular matrix consisting of microfibrils. The neural crest and sclerotome cells migrate into the large matrix-filled extracellular space surrounding the neural tube and notochord, apparently using microfibril microfibril bundles as substratum. The cells exhibit pseudopodia which are closely associated with the matrix fibrils. The fibrils around the notochord show a spatial arrangement indicating that the sclerotome cells are contact-guided to their subsequent positions. Mutual cell contacts, including those established by cell processes, frequently show cytoplasmic electron dense plaques at adjacent membranes. These small "plaque contacts" might be correlated to contact inhibition of locomotion between the cells and participate in the guidance of cells. The growth cones of extending axons exhibit filopodia contacting both surrounding mesenchyme cells and extracellular fibrils. The orientation of the axons might thus be affected by contacts with cell surfaces as well as with extracellular material.

Animals↗