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Skeletal muscle microcirculatory response to rat alpha-calcitonin gene-related peptide.

We used in vivo video microscopy to determine the effect of increasing doses of rat alpha-calcitonin gene-related peptide (rCGRP) on rat cremaster muscle arterioles in the presence or absence of the nitric oxide synthase inhibitor N-omega-nitro-L-arginine (L-NNA). Male Sprague-Dawley rats (118-148 g) were anaesthetized with pentobarbital, and neurovascularly intact cremaster muscles were imaged. Changes in the diameter, erythrocyte velocity and volume flow in second-(A2), third-(A3), and fourth-(A4) order arterioles were determined. To produce uniform arteriolar tone, the cremaster preparation was challenged with norepinephrine (NE: 10(-7) M). L-NNA (10(-4) M), which was shown to inhibit acetylcholine-(ACh: 10(-6) M) induced arteriolar dilations, was added to 16 of the preparations. Preparations were then challenged by adding cumulative log concentrations of rCGRP (10(-12)-10-7) M; n = 16) or an equivalent volume of vehicle (n = 19) to the bath. Following rCGRP challenge, arterioles were maximally dilated with 10(-5) M nitroprusside (NP). rCGRP caused significant dose-dependent increases in erythrocyte velocity and volume flow in A2 arterioles, and in diameter, velocity, and volume flow in A3 and A4 arterioles, by 10(-8) M, when compared with vehicle-treated controls. L-NNA had no significant effect on rCGRP-induced responses. These data indicate that rCGRP causes dose-dependent dilation of skeletal muscle resistance arterioles at a concentration similar to that observed in larger vessels. This dilation does not appear to be dependent on the vascular production of nitric oxide from L-arginine.

Acetylcholine↗

Infrared videomicroscopy: a new look at neuronal structure and function.

Brain slices were introduced as a standard preparation for neurophysiological experiments some 20 years ago. A drawback of this preparation compared with cell culture has been the difficulty to visualize individual neurones in standard thick slices. This problem has been overcome by the use of infrared videomicroscopy. Neurones in slices can now be visualized in great detail, and neuronal processes can be patch-clamped under direct visual control. Infrared video-microscopy has also been applied successfully to other fields of neuroscience such as neuronal development and neurotoxicity. A further development of infrared videomicroscopy enables one to visualize the spread of excitation in slices making the technique a tool for the direct investigation of neuronal function.

Animals↗

Variability of the thrombin- and ADP-induced Ca2+ response among human platelets measured using fluo-3 and fluorescent videomicroscopy.

The intracellular free Ca2+ concentration ([Ca2+]cyt) of individual human platelets localized between siliconized glass cover slips was determined at rest and after stimulation with thrombin and ADP using the Ca2+ indicator fluo-3 (0.97 +/- 0.30 mmol/l cell volume) with fluorescence video microscopy. Resting [Ca2+]cyt in the presence of 2 mM external Ca2+ showed only small inter-platelet variability ([Ca2+]cyt = 86 +/- 30 (S.D.) nM). Resting [Ca2+]cyt of individual fluo-3-loaded platelets measured as a function of time had a S.D. of 10 nM or 12% (S.D./mean). Individual platelets showed no affinity for the siliconized support and their [Ca2+]cyt showed no tendency to oscillate in either the resting or in the activated state. When 0.2 U/ml thrombin or 20 microM ADP were added, all platelets showed a characteristic Ca2+ transient whereby [Ca2+]cyt increased to peak values within 8-12 sec and then declined. The Ca2+ transients measured with fluo-3 were in approximate synchrony but peak [Ca2+]cyt values showed large inter-platelet variability. The ensemble average peak [Ca2+]cyt for thrombin and ADP were 672 +/- 619 (S.D.) nM and 640 +/- 642 (S.D.) nM, respectively. Thus inter-platelet variations (S.D./mean) were 92% or 100% as large as the average measured values. Mathematically-constructed averages of the single platelet experiments agreed reasonably well with platelet-averaged values obtained in parallel experiments with stirred platelet suspensions in a plastic cuvette, measured with a conventional spectrofluorometer. Peak [Ca2+]cyt values reflecting dense tubular Ca2+ release alone (external Ca2+ removed) also showed large interplatelet variation (171 +/- 105 (S.D.) nM with thrombin and 183 +/- 134 (S.D.) nM with ADP). Dense tubular Ca2+ release induced by cyclopiazonic acid (a dense tubular Ca2+-ATPase inhibitor) gave peak [Ca2+]cyt of 289 +/- 170 nM. Thus the size of the dense tubular Ca2+ pool has an inter-platelet variation of 59% (S.D./mean). Variability of the dense tubular pool size accounts for some, but not all, of the large interplatelet variation in peak (Ca2+]cyt seen with thrombin and ADP activation.

Adenosine Diphosphate↗

Increased skin capillary density in treated essential hypertensive patients.

BACKGROUND: Microvascular rarefaction is a hallmark of essential hypertension. We measured the skin capillary density in nondiabetic hypertensive subjects with effective antihypertensive treatment and evaluated possible correlations with arterial blood pressure (BP). METHODS: This cross-sectional observational study included 76 (55 +/- 1 years) consecutive outpatients with essential hypertension under chronic antihypertensive drug treatment (BP < 140/90 mm Hg), 24 age- and sex-matched patients with recently discovered and never-treated hypertension and 70 normotensive (BP < 140/90 mm Hg) age- and sex-matched healthy controls. We used intravital video-microscopy to measure basal and maximal (during venous congestion) skin capillary densities in the dorsum of the fingers. Aortic stiffness was evaluated using pulse wave velocity and central aortic pressure calculated from radial artery applanation tonometry. RESULTS: Baseline and maximal capillary densities (number/mm2) were significantly lower (59.6 +/- 2.0 and 62.0 +/- 1.9) in untreated than in treated hypertensive patients (74.0 +/- 1.4 and 79.4 +/- 1.5; P < .001) and than in normotensives (68.2 +/- 1.5 and 72.4 +/- 1.5; P < .001). Based on multiple regression analysis, after adjustment to tobacco consumption, aortic (and not brachial) systolic BP was inversely correlated with basal and postocclusive capillary densities in normotensive subjects. In hypertensives, this correlation disappears and capillary density was influenced by two independent variables, antihypertensive drug treatment and overweight. CONCLUSIONS: In nondiabetic hypertensive patients, capillary density is reduced in association with a cluster of cardiovascular risk factors involving tobacco consumption and obesity. The finding of an increased capillary density in effectively treated antihypertensives suggests that a cause-to-effect relationship between BP and capillary density should be evaluated in a long-term prospective follow-up.

Antihypertensive Agents↗

Integrin-dependent protein tyrosine phosphorylation is a key regulatory event in collagen-IV-mediated adhesion and proliferation of human lung tumor cell line, Calu-1.

BACKGROUND: The clinical phenomenon of lung cancer metastasis to specific target organs is believed to be a direct interaction between tumor cells and extracellular matrix components. During invasion, tumor cells attach to the basement membrane protein, collagen type IV, degrade it, migrate through blood vessels, and adhere to extracellular matrix proteins. METHODS: Four nonsmall-cell lung cancer cells were tested for adhesion, proliferation, migration and morphologic alterations on collagen type IV matrix by immunoprecipitation, Western blotting, phase contrast and time lapse video microscopy. RESULTS: Collagen type IV promoted Calu-1 cell adhesion (< 15 minutes) and motility (< 6 hours) without any significant effect on proliferation. beta(1)-integrin is essential for collagen type IV adhesion and 8 to 10 fold higher expression of beta1-integrin on the surface of Calu-1 cells was identified. A protein tyrosine phosphatase inhibitor, peroxyvanadate, caused 50% inhibition in the adhesion process within 5 minutes but exposure to 60 micromol/L genistein for 72 hours, a protein tyrosine kinase inhibitor, drastically inhibits Calu-1 cell proliferation (> 70%). We examined the influence of beta1-integrin, peroxyvanadate and genistein on the spreading morphogenesis of Calu-1 cells on Collagen type IV. Use of either 1 microg of anti beta1-integrin inhibitory antibody (P5D2), 100 micromol/L peroxyvanadate or 60 micromol/L genistein had dramatic influence on the spreading of Calu-1 cells. Finally, Focal adhesion kinase was identified as a phosphoprotein target. CONCLUSIONS: We have characterized an in vitro model of matrix-specific binding of a lung cancer cell line, Calu-1 to Coll IV. Calu-1 cells use primarily a beta1-integrin mediated intracellular tyrosine phosphorylation phenomenon as the key regulatory mechanism for its binding advantage to Coll IV matrix.

Carcinoma, Non-Small-Cell Lung↗

Live cell imaging reveals distinct roles in cell cycle regulation for Nek2A and Nek2B.

Two splice variants of Nek2 kinase, a member of the NIMA-related family, have been identified as Nek2A and Nek2B. Nek2A regulates centrosome disjunction, spindle formation checkpoint signaling, and faithful chromosome segregation. A specific role for Nek2B has not yet been identified. Here, we have examined the distinct roles of Nek2A and Nek2B using timelapse video microscopy to follow the fate of cells progressing through the cell cycle in the absence of either Nek2A or Nek2B. We show that the down-regulation of Nek2B leads to a mitotic delay in the majority of cells. Upon exiting mitosis, cells exhibit mitotic defects such as the formation of multinucleated cells. Such phenotypes are not observed in cells that exit mitosis in the absence of Nek2A. These observations suggest that Nek2B may be required for the execution of mitotic exit.

Alternative Splicing↗

Subcellular localization and dynamics of MysPDZ (Myo18A) in live mammalian cells.

MysPDZ is an unconventional myosin belonging to the class XVIII myosin containing a KE (lysine and glutamine)-rich domain and a PDZ domain, which codistributes with actin fibers partially without any canonical actin binding sequence in its myosin head domain. Recently, we reported the identification of a novel isoform of MysPDZ lacking these domains and exhibiting subcellular localization and expression profile different from the original form of MysPDZ. In order to delineate domains directing the subcellular localization of MysPDZ, we performed co-immunoprecipitation experiments and image analyses using mutants of MysPDZ fused with enhanced yellow fluorescent protein. Co-immunoprecipitation analyses showed that MysPDZ can self-associate through its C-terminus coiled-coil domain and the KE-rich domain mediates the interaction with actin. We observed by image analyses that the codistribution with actin fibers and the localization in inner surface of cell membrane of MysPDZ are controlled by the KE-rich domain and the PDZ domain, respectively. Time lapse video microscopy showed that MysPDZ in the cytoplasm moves randomly and rapidly within short range and is allocated to a subcellular compartment without ATP hydrolysis by MysPDZ. This suggests that MysPDZ is a protein which is unlike most unconventional myosins. Our study uncovers a novel role of the KE-rich and PDZ domains in directing subcellular localization and also contributes to a better understanding of functional differences in MysPDZ isoforms.

Actins↗

Time-lapse analysis of retinal differentiation.

The availability of new vital markers and the improvements in time-lapse video microscopy have increased our ability to observe developmental events in the retina while they are happening. Using this approach, advances have been made in the understanding of important issues such as how division patterns relate to cell fate determination, how post-mitotic progenitors reach their correct retinal layers, and finally, how retinal ganglion cell axons navigate out of the retina and to their final targets in the midbrain.

Animals↗

Sumo1 conjugates mitochondrial substrates and participates in mitochondrial fission.

Mitochondrial fission requires the evolutionarily conserved dynamin related protein (DRP1), which is recruited from the cytosol to the mitochondrial outer membrane to coordinate membrane scission. Currently, the mechanism of recruitment and assembly of DRP1 on the mitochondria is unclear. Here, we identify Ubc9 and Sumo1 as specific DRP1-interacting proteins and demonstrate that DRP1 is a Sumo1 substrate. In addition, a surprising number of Sumo1 conjugates were observed in the mitochondrial fractions, suggesting that sumoylation is a common mitochondrial modification. Video microscopy demonstrates that YFP:Sumo1 is often found at the site of mitochondrial fission and remains tightly associated to the tips of fragmented mitochondria. Consistent with this, fluorescence microscopy revealed that a portion of total cytosolic YFP:Sumo1 colocalizes with endogenous mitochondrial DRP1. Finally, transient transfection of Sumo1 dramatically increases the level of mitochondrial fragmentation. Analysis of endogenous DRP1 levels indicates that overexpression of Sumo1 specifically protects DRP1 from degradation, resulting in a more stable, active pool of DRP1, which at least partially accounts for the excess fragmentation. Together, these data are the first to identify a function for Sumo1 on the mitochondria and suggest a novel role for the participation of Sumo1 in mitochondrial fission.

Animals↗

Terminal cytokinesis events uncovered after an RNAi screen.

Much of our understanding of animal cell cytokinesis centers on the regulation of the equatorial acto-myosin contractile ring that drives the rapid ingression of a deep cleavage furrow. However, the central part of the mitotic spindle collapses to a dense structure that impedes the furrow and keeps the daughter cells connected via an intercellular bridge. Factors involved in the formation, maintenance, and resolution of this bridge are largely unknown. Using a library of 7,216 double-stranded RNAs (dsRNAs) representing the conserved genes of Drosophila, we performed an RNA interference (RNAi) screen for cytokinesis genes in Schneider's S2 cells. We identified both familiar and novel genes whose inactivation induced a multi-nucleate phenotype. Using live video microscopy, we show that three genes: anillin, citron-kinase (CG10522), and soluble N-ethylmaleimide sensitive factor (NSF) attachment protein (alpha-SNAP), are essential for the terminal (post-furrowing) events of cytokinesis. anillin RNAi caused gradual disruption of the intercellular bridge after furrowing; citron-kinase RNAi destabilized the bridge at a later stage; alpha-SNAP RNAi caused sister cells to fuse many hours later and by a different mechanism. We have shown that the stability of the intercellular bridge is essential for successful cytokinesis and have defined genes contributing to this stability.

Actins↗

Rho-kinase controls cell shape changes during cytokinesis.

BACKGROUND: Animal cell cytokinesis is characterized by a sequence of dramatic cortical rearrangements. How these are coordinated and coupled with mitosis is largely unknown. To explore the initiation of cytokinesis, we focused on the earliest cell shape change, cell elongation, which occurs during anaphase B and prior to cytokinetic furrowing. RESULTS: Using RNAi and live video microscopy in Drosophila S2 cells, we implicate Rho-kinase (Rok) and myosin II in anaphase cell elongation. rok RNAi decreased equatorial myosin II recruitment, prevented cell elongation, and caused a remarkable spindle defect where the spindle poles collided with an unyielding cell cortex and the interpolar microtubules buckled outward as they continued to extend. Disruption of the actin cytoskeleton with Latrunculin A, which abolishes cortical rigidity, suppressed the spindle defect. rok RNAi also affected furrowing, which was delayed and slowed, sometimes distorted, and in severe cases blocked altogether. Codepletion of the myosin binding subunit (Mbs) of myosin phosphatase, an antagonist of myosin II activation, only partially suppressed the cell-elongation defect and the furrowing delay, but prevented cytokinesis failures induced by prolonged rok RNAi. The marked sensitivity of cell elongation to Rok depletion was highlighted by RNAi to other genes in the Rho pathway, such as pebble, racGAP50C, and diaphanous, which had profound effects on furrowing but lesser effects on elongation. CONCLUSIONS: We show that cortical changes underlying cell elongation are more sensitive to depletion of Rok and myosin II, in comparison to other regulators of cytokinesis, and suggest that a distinct regulatory pathway promotes cell elongation.

Anaphase↗

Human platelets exhibit chemotaxis using functional N-formyl peptide receptors.

OBJECTIVE: Activated platelets participate in inflammatory and microbicidal processes by upregulation of surface selectins, shedding of CD40 ligand, and release of platelet microbicidal proteins and microparticles. Given their myeloid lineage, we hypothesized that platelets express functional N-formyl peptide receptors and respond to the bacterially derived chemotactic peptide N-formyl peptide with gradient-driven chemotaxis. METHODS AND RESULTS: Here we show specific binding of N-formyl peptides to the surface of activated platelets. Platelet expression and function of the formyl peptide receptor, FPR, was verified by RT-PCR of the differentiated megakaryocyte MEG-01 cell line, immunoblotting of platelet proteins, and calcium mobilization in platelets with formyl peptide binding. Furthermore, we demonstrate gradient-driven chemotaxis of platelets by video microscopy and transwell migration toward formyl peptides. We also show that endogenous formyl peptides, released by eukaryotic mitochondria from necrotic cells, induce chemotaxis using formyl peptide receptors expressed by thrombin-activated platelets. Conversely, supernatants from cells undergoing apoptotic cell death do not induce platelet chemotaxis. Platelet chemotaxis to formyl peptides was blocked with FPR-specific antibody as well as by pertussis toxin inhibition of the formyl peptide G-coupled receptor. CONCLUSION: These data establish a new role for platelets in host defense and suggest reexamination of their active function in microbicidal and other host defense activities.

Aorta↗

Entamoeba histolytica: differences in phagosome acidification and degradation between attenuated and virulent strains.

Phagocytosis is the important virulent determinant of the enteric protozoan parasite Entamoeba histolytica. We compared the kinetics of phagosome maturation of attenuated and highly-virulent strains of E. histolytica using video microscopy. Phagosomes of attenuated strains were acidified rapidly within 2 min after phagosome formation (at the rate of 0.96 pH/min), persisted at pH 4.46+/-0.13, and degraded ingested GFP-Leishmania very efficiently (90-94% GFP fluorescence was lost in 30 min), while phagosomes of highly-virulent strains were acidified slowly (0.69 pH/min), persisted at 5.11+/-0.23, and degraded GFP less efficiently (60-71% decrease). These results suggest that efficiency of phagosome maturation is most probably inversely correlated with apparent virulence.

Animals↗

Prolonged costimulation is required for naive T cell activation.

Costimulation by members of the B7 family of molecules is critical for the activation of naive CD4+ T cells. While prolonged TCR signaling is necessary for T cell activation, the duration of costimulatory signals required has not been established. In this study, murine bone marrow-derived dendritic cells (DC) and naïve CD4+ T cells were used to determine the temporal costimulatory requirements for naive T cell activation. By blocking CD80/CD86 costimulation at various time points during DC-T cell interaction and using the CFSE technique to assess the dynamics of T cell proliferation, we found that prolonged costimulation was required for naive T cells to enter and progress through the cell cycle over a wide range of peptide concentrations. Prolonged costimulation was also important for IL-2 production and CD25/CD69 expression by naive T cells. Video microscopy demonstrated that DC and naive T cells formed stable conjugates that persisted for more than 6 h. Thus, persistent CD80/CD86 signaling during prolonged interactions with DC allows naive T cells to enter the cell cycle and programs the daughter cells to undergo subsequent divisions.

Animals↗

New method to measure water permeability in emptied-out Xenopus oocytes controlling conditions on both sides of the membrane.

Membrane water permeability is habitually calculated from volume changes in Xenopus laevis oocytes during external osmotic challenges. Nevertheless, this approach is limited by the uncertainty on the oocyte internal composition. To circumvent this limitation a new experimental set up is introduced where the cell membrane of an emptied-out oocyte was mounted as a diaphragm between two chambers. In its final configuration the oocyte membrane was part of a closed compartment and net water movements induced swelling or shrinking of it. Volume changes were followed by video-microscopy and digitally recorded. In this manner, water movements could be continuously monitored while controlling chemical composition and hydrostatic pressure on both sides of the membrane. Using this novel experimental approach an increasing hydrostatic pressure gradient was applied to both mature (stage VI) and immature (stage IV) oocytes. The relative maximal volume change tolerated before disruption was similar in both cases (1.26+/-0.07 and 1.27+/-0.03 respectively) and similar to those previously reported under maximal osmotic stress. Nevertheless the osmotic permeability coefficient (P(OSM)) in mature oocytes ((1.72+/-0.58) x 10(-3) cm s(-1); n=6) was significantly lower than in immature oocytes ((5.18+/-0.59) x 10(-3) cm s(-1), n=5; p<0.005).

Animals↗

Clustering transmembrane-agrin induces filopodia-like processes on axons and dendrites.

The transmembrane form of agrin (TM-agrin) is primarily expressed in the CNS, particularly on neurites. To analyze its function, we clustered TM-agrin on neurons using anti-agrin antibodies. On axons from the chick CNS and PNS as well as on axons and dendrites from mouse hippocampal neurons anti-agrin antibodies induced the dose- and time-dependent formation of numerous filopodia-like processes. The processes appeared within minutes after antibody addition and contained a complex cytoskeleton. Formation of processes required calcium, could be inhibited by cytochalasine D, but was not influenced by staurosporine, heparin or pervanadate. Time-lapse video microscopy revealed that the processes were dynamic and extended laterally along the entire length of the neuron. The lateral processes had growth cones at their tips that initially adhered to the substrate, but subsequently collapsed and were retracted. These data provide the first evidence for a specific role of TM-agrin in shaping the cytoskeleton of neurites in the developing nervous system.

Agrin↗

Cell behavior and cell-cell communication during fruiting body morphogenesis in Myxococcus xanthus.

Formation of spatial patterns of cells from a mass of initially identical cells is a recurring theme in developmental biology. The dynamics that direct pattern formation in biological systems often involve morphogenetic cell movements. An example is fruiting body formation in the gliding bacterium Myxococcus xanthus in which an unstructured population of identical cells rearranges into an asymmetric, stable pattern of multicellular fruiting bodies in response to starvation. Fruiting body formation depends on changes in organized cell movements from swarming to aggregation. The aggregation process is induced and orchestrated by the cell-surface associated 17 kDa C-signal protein. C-signal transmission depends on direct contact between cells. Evidence suggests that C-signal transmission is geometrically constrained to cell ends and that productive C-signal transmission only occurs when cells engage in end-to-end contacts. Here, we review recent progress in the understanding of the pattern formation process that leads to fruiting body formation. Gliding motility in M. xanthus involves two polarly localized gliding machines, the S-machine depends on type IV pili and the A-machine seems to involve a slime extrusion mechanism. Using time-lapse video microscopy the gliding motility parameters controlled by the C-signal have been identified. The C-signal induces cells to move with increased gliding speeds, in longer gliding intervals and with decreased stop and reversal frequencies. The combined effect of the C-signal dependent changes in gliding motility behaviour is an increase in the net-distance travelled by a cell per minute. The identification of the motility parameters controlled by the C-signal in combination with the contact-dependent C-signal transmission mechanism have allowed the generation of a qualitative model for C-signal induced aggregation. In this model, the directive properties of the C-signal are a direct consequence of the contact-dependent signal-transmission mechanism, which is a local event involving direct contact between cells that results in a global organization of cells. This pattern formation process does not depend on a diffusible substance. Rather it depends on a cell-surface associated signal to direct the cells appropriately.

Bacterial Proteins↗

Novel syngeneic pseudo-orthotopic prostate cancer model: vascular, mitotic and apoptotic responses to castration.

We describe a novel syngeneic "pseudo-orthotopic" in vivo model of prostate cancer progression. Our model uses the dorsal skinfold chamber technique with fluorescence video microscopy and TRAMP-C2 tumor cells. The cells were transfected with a histone H2B-GFP fusion protein, permitting real-time measurement of tumor size, as well as mitotic and apoptotic indices. To generate a "pseudo-orthotopic" milieu, pieces of prostate tissue (10-15 mm2) from donor mice were implanted into the chambers of C57BL/6 mice. The prostate tissue grafted into the chambers retained its native vasculature, as determined by transplantation of prostate tissue from GFP transgenic mice. TRAMP-C2 prostate cancer tumor spheroids (25,000 cells) were implanted in the chamber. Without prostate tissue, TRAMP-C2 prostate tumors were poorly angiogenic, displayed low mitotic and apoptotic indices (0.7 x 10(-4)), and no significant tumor growth could be detected. TRAMP-C2 tumors growing on transplanted prostate tissue in the chamber on the other hand had mitotic indices in the order of 1.6 x 10(-4) and apoptotic indices in the order of 0.8 x 10(-4). Furthermore, tumors with stroma were highly angiogenic, and were fully vascularized within 7-10 days. During a 4-week observation period, the number of tumor cells increased by nearly 300%. We used the model to study the effects of surgical castration. The most profound response was a rapid vascular regression of the tumor vasculature. Castration also increased apoptotic indices within the tumor without significant changes in mitosis. This model may be utilized for the rapid analysis of new therapeutic candidates against prostate cancer.

Adenocarcinoma↗