scholarly journals Slipping or Gripping? Fluorescent Speckle Microscopy in Fish Keratocytes Reveals Two Different Mechanisms for Generating a Retrograde Flow of Actin

2005 ◽  
Vol 16 (2) ◽  
pp. 507-518 ◽  
Author(s):  
Carlos Jurado ◽  
John R. Haserick ◽  
Juliet Lee
Keyword(s):  
Flow Rate ◽  
Potent Inhibitor ◽  
Myosin Ii ◽  
Force Production ◽  
Traction Force ◽  
The Other ◽  
Force Generation ◽  
Retrograde Flow ◽  
Transfected Cells ◽  
The Relationship

Fish keratocytes can generate rearward directed traction forces within front portions of the lamellipodium, suggesting that a retrograde flow of actin may also occur here but this was not detected by previous photoactivation experiments. To investigate the relationship between retrograde flow and traction force generation, we have transfected keratocytes with GFP-actin and used fluorescent speckle microscopy, to observe speckle flow. We detected a retrograde flow of actin within the leading lamellipodium that is inversely proportional to both protrusion rate and cell speed. To observe the effect of reducing contractility, we treated transfected cells with ML7, a potent inhibitor of myosin II. Surprisingly, ML7 treatment led to an increase in retrograde flow rate, together with a decrease in protrusion and cell speed, but only in rapidly moving cells. In slower moving cells, retrograde flow decreased, whereas protrusion rate and cell speed increased. These results suggest that there are two mechanisms for producing retrograde flow. One involves slippage between the cytoskeleton and adhesions, that decreases traction force production. The other involves slippage between adhesions and the substratum, which increases traction force production. We conclude that a biphasic relationship exists between retrograde actin flow and adhesiveness in moving keratocytes.

scholarly journals Crosstalk between myosin II and formin functions in the regulation of force generation and actomyosin dynamics in stress fibers

2021 ◽  
Author(s):  
Yukako Nishimura ◽  
Shidong Shi ◽  
Qingsen Li ◽  
Alexander D. Bershadsky ◽  
Virgile Viasnoff
Keyword(s):  
Contractile Activity ◽  
Myosin Ii ◽  
Focal Adhesions ◽  
Traction Force ◽  
Stress Fiber ◽  
Force Generation ◽  
Stress Fibers ◽  
Force Microscopy ◽  
Fiber Dynamics ◽  
The Relationship

REF52 fibroblasts have a well-developed contractile machinery, the most prominent elements of which are actomyosin stress fibers with highly ordered organization of actin and myosin IIA filaments. The relationship between contractile activity and turnover dynamics of stress fibers is not sufficiently understood. Here, we simultaneously measured the forces exerted by stress fibers (using traction force microscopy or micropillar array sensors) and the dynamics of actin and myosin (using photoconversion-based monitoring of actin incorporation and high-resolution fluorescence microscopy of myosin II light chain). Our data revealed new features of the crosstalk between myosin II-driven contractility and stress fiber dynamics. During normal stress fiber turnover, actin incorporated all along the stress fibers and not only at focal adhesions. Incorporation of actin into stress fibers/focal adhesions, as well as actin and myosin II filaments flow along stress fibers, strongly depends on myosin II activity. Myosin II-dependent generation of traction forces does not depend on incorporation of actin into stress fibers per se, but still requires formin activity. This previously overlooked function of formins in maintenance of the actin cytoskeleton connectivity could be the main mechanism of formin involvement in traction force generation.

scholarly journals Growth cone behavior and production of traction force.

1990 ◽  
Vol 111 (5) ◽  
pp. 1949-1957 ◽  
Author(s):  
S R Heidemann ◽  
P Lamoureux ◽  
R E Buxbaum
Keyword(s):  
Growth Cone ◽  
Contractile Activity ◽  
Glass Fibers ◽  
Force Production ◽  
Traction Force ◽  
Dorsal Surface ◽  
Growth Cones ◽  
Retrograde Flow ◽  
Cortical Actin ◽  
Over The Top

The growth cone must push its substrate rearward via some traction force in order to propel itself forward. To determine which growth cone behaviors produce traction force, we observed chick sensory growth cones under conditions in which force production was accommodated by movement of obstacles in the environment, namely, neurites of other sensory neurons or glass fibers. The movements of these obstacles occurred via three, different, stereotyped growth cone behaviors: (a) filopodial contractions, (b) smooth rearward movement on the dorsal surface of the growth cone, and (c) interactions with ruffling lamellipodia. More than 70% of the obstacle movements were caused by filopodial contractions in which the obstacle attached at the extreme distal end of a filopodium and moved only as the filopodium changed its extension. Filopodial contractions were characterized by frequent changes of obstacle velocity and direction. Contraction of a single filopodium is estimated to exert 50-90 microdyn of force, which can account for the pull exerted by chick sensory growth cones. Importantly, all five cases of growth cones growing over the top of obstacle neurites (i.e., geometry that mimics the usual growth cone/substrate interaction), were of the filopodial contraction type. Some 25% of obstacle movements occurred by a smooth backward movement along the top surface of growth cones. Both the appearance and rate of movements were similar to that reported for retrograde flow of cortical actin near the dorsal growth cone surface. Although these retrograde flow movements also exerted enough force to account for growth cone pulling, we did not observe such movements on ventral growth cone surfaces. Occasionally obstacles were moved by interaction with ruffling lamellipodia. However, we obtained no evidence for attachment of the obstacles to ruffling lamellipodia or for directed obstacle movements by this mechanism. These data suggest that chick sensory growth cones move forward by contractile activity of filopodia, i.e., isometric contraction on a rigid substrate. Our data argue against retrograde flow of actin producing traction force.

scholarly journals Phagocytic 'teeth' and myosin-II 'jaw' power target constriction during phagocytosis

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Daan Vorselen ◽  
Sarah R Barger ◽  
Yifan Wang ◽  
Wei Cai ◽  
Julie A Theriot ◽  
...  
Keyword(s):  
Myosin Ii ◽  
Traction Force ◽  
Light Sheet ◽  
Force Generation ◽  
Actin Dynamics ◽  
Force Microscopy ◽  
Light Sheet Microscopy ◽  
Macrophage Phagocytosis ◽  
Actin Protrusions

Phagocytosis requires rapid actin reorganization and spatially controlled force generation to ingest targets ranging from pathogens to apoptotic cells. How actomyosin activity directs membrane extensions to engulf such diverse targets remains unclear. Here, we combine lattice light-sheet microscopy (LLSM) with microparticle traction force microscopy (MP-TFM) to quantify actin dynamics and subcellular forces during macrophage phagocytosis. We show that spatially localized forces leading to target constriction are prominent during phagocytosis of antibody-opsonized targets. This constriction is largely driven by Arp2/3-mediated assembly of discrete actin protrusions containing myosin 1e and 1f ('teeth') that appear to be interconnected in a ring-like organization. Contractile myosin-II activity contributes to late-stage phagocytic force generation and progression, supporting a specific role in phagocytic cup closure. Observations of partial target eating attempts and sudden target release via a popping mechanism suggest that constriction may be critical for resolving complex in vivo target encounters. Overall, our findings present a phagocytic cup-shaping mechanism that is distinct from cytoskeletal remodeling in 2D cell motility and may contribute to mechanosensing and phagocytic plasticity.

scholarly journals UV microbeam irradiations of the mitotic spindle. II. Spindle fiber dynamics and force production.

1990 ◽  
Vol 111 (4) ◽  
pp. 1505-1518 ◽  
Author(s):  
T P Spurck ◽  
O G Stonington ◽  
J A Snyder ◽  
J D Pickett-Heaps ◽  
A Bajer ◽  
...  
Keyword(s):  
Mitotic Spindle ◽  
Force Production ◽  
The Other ◽  
Force Generation ◽  
Spindle Fiber ◽  
Spindle Microtubule ◽  
Microtubule Stability ◽  
Fiber Dynamics ◽  
Spindle Fibers

Metaphase and anaphase spindles in cultured newt and PtK1 cells were irradiated with a UV microbeam (285 nM), creating areas of reduced birefringence (ARBs) in 3 s that selectively either severed a few fibers or cut across the half spindle. In either case, the birefringence at the polewards edge of the ARB rapidly faded polewards, while it remained fairly constant at the other, kinetochore edge. Shorter astral fibers, however, remained present in the enlarged ARB; presumably these had not been cut by the irradiation. After this enlargement of the ARB, metaphase spindles recovered rapidly as the detached pole moved back towards the chromosomes, reestablishing spindle fibers as the ARB closed; this happened when the ARB cut a few fibers or across the entire half spindle. We never detected elongation of the cut kinetochore fibers. Rather, astral fibers growing from the pole appeared to bridge and then close the ARB, just before the movement of the pole toward the chromosomes. When a second irradiation was directed into the closing ARB, the polewards movement again stopped before it restarted. In all metaphase cells, once the pole had reestablished connection with the chromosomes, the unirradiated half spindle then also shortened to create a smaller symmetrical spindle capable of normal anaphase later. Anaphase cells did not recover this way; the severed pole remained detached but the chromosomes continued a modified form of movement, clumping into a telophase-like group. The results are discussed in terms of controls operating on spindle microtubule stability and mechanisms of mitotic force generation.

scholarly journals Role of Myosin II in Axon Outgrowth

2003 ◽  
Vol 51 (4) ◽  
pp. 421-428 ◽  
Author(s):  
Jacquelyn Brown ◽  
Paul C. Bridgman
Keyword(s):  
Extracellular Matrix ◽  
Cell Adhesion ◽  
Myosin Ii ◽  
Traction Force ◽  
Growth Cones ◽  
Matrix Proteins ◽  
Retrograde Flow ◽  
Complex Interactions ◽  
Cell Adhesion Proteins

The initial stages of nerve outgrowth carried out by growth cones occur in three fundamental cyclic steps. Each of these steps appears to require myosin II activity to variable degrees. The steps include the following: (a) exploration, involving extensions and retractions that are driven and controlled by the interaction of actin retrograde flow and polymerization; (b) adhesion of new extensions to the substrate, which has been shown to be mediated by complex interactions between extracellular matrix proteins, cell adhesion proteins, and the actin cytoskeleton; and (c) traction force generated during forward advance of the growth cone, resulting in the production of tension on the neurite.

scholarly journals Phagocytic 'teeth' and myosin-II 'jaw' power target constriction during phagocytosis

2021 ◽  
Author(s):  
Daan Vorselen ◽  
Sarah R. Barger ◽  
Yifan Wang ◽  
Wei Cai ◽  
Julie A. Theriot ◽  
...  
Keyword(s):  
Myosin Ii ◽  
Traction Force ◽  
Light Sheet ◽  
Force Generation ◽  
Actin Dynamics ◽  
Force Microscopy ◽  
Light Sheet Microscopy ◽  
Macrophage Phagocytosis ◽  
Actin Protrusions

Phagocytosis requires rapid actin reorganization and spatially controlled force generation to ingest targets ranging from pathogens to apoptotic cells. How actomyosin activity directs membrane extensions to engulf such diverse targets remains unclear. Here, we combine lattice light-sheet microscopy (LLSM) with microparticle traction force microscopy (MP-TFM) to quantify actin dynamics and subcellular forces during macrophage phagocytosis. We show that spatially localized forces leading to target constriction are prominent during phagocytosis of antibody-opsonized targets. This constriction is largely mediated by Arp2/3-mediated assembly of discrete actin protrusions containing myosin 1e and 1f ('teeth') that are interconnected in a ring-like organization. Contractile myosin-II activity contributes to late-stage phagocytic force generation and progression, suggesting a specific role in phagocytic cup closure. Observations of partial target eating attempts and sudden target release via a popping mechanism suggest that constriction may be critical for resolving complex in vivo target encounters. Overall, our findings suggest a phagocytic cup-shaping mechanism that is distinct from cytoskeletal remodeling in 2D cell motility and may contribute to mechanosensing and phagocytic plasticity.

The Relationship Between Suicidal Thinking and Dating Violence in a Sample of Adolescent Abortion Patients

Crisis ◽  
2011 ◽  
Vol 32 (5) ◽  
pp. 246-253 ◽  
Author(s):  
Gretchen E. Ely ◽  
William R. Nugent ◽  
Julie Cerel ◽  
Mholi Vimbba
Keyword(s):  
Unintended Pregnancy ◽  
Dating Violence ◽  
Young Women ◽  
Psychosocial Problems ◽  
The Other ◽  
Assessment Scale ◽  
Adolescent Dating Violence ◽  
Adolescent Relationships ◽  
Suicidal Thinking ◽  
The Relationship

Background: The relationship between suicidal thinking and adolescent dating violence has not been previously explored in a sample of adolescent abortion patients. Aims: This paper highlights a study where the relationship between dating violence and severity of suicidal thinking was examined in a sample of 120 young women ages 14–21 seeking to terminate an unintended pregnancy. Methods: The Multidimensional Adolescent Assessment Scale and the Conflict in Adolescent Relationships Scale was used to gather information about psychosocial problems and dating violence so that the relationship between the two problems could be examined, while controlling for the other psychosocial problems. Results: The results suggest that dating violence was related to severity of suicidal thinking, and that the magnitude of this relationship was moderated by the severity of problems with aggression. Conclusions: Specifically, as the severity of participant’s general problems with aggression increased, the magnitude of the relationship between dating violence and severity of suicidal thinking increased. Limitations of the study and implications for practice are discussed.

Emotional Impact Feedback Changes How We Remember Negative Autobiographical Experiences

2010 ◽  
Vol 57 (5) ◽  
pp. 354-359 ◽  
Author(s):  
Melanie K. T. Takarangi ◽  
Deryn Strange
Keyword(s):  
Well Being ◽  
The Other ◽  
Personal Perspective ◽  
Emotional Impact ◽  
Potential Mechanism ◽  
Negative Experiences ◽  
Negative Memory ◽  
The Relationship ◽  
Negative Memories ◽  
Over Time

When people are told that their negative memories are worse than other people’s, do they later remember those events differently? We asked participants to recall a recent negative memory then, 24 h later, we gave some participants feedback about the emotional impact of their event – stating it was more or less negative compared to other people’s experiences. One week later, participants recalled the event again. We predicted that if feedback affected how participants remembered their negative experiences, their ratings of the memory’s characteristics should change over time. That is, when participants are told that their negative event is extremely negative, their memories should be more vivid, recollected strongly, and remembered from a personal perspective, compared to participants in the other conditions. Our results provide support for this hypothesis. We suggest that external feedback might be a potential mechanism in the relationship between negative memories and psychological well-being.

Haematocrit: Relationships with Blood Lipids, Blood Pressure and other Cardiovascular Risk Factors

1994 ◽  
Vol 72 (01) ◽  
pp. 058-064 ◽  
Author(s):  
Goya Wannamethee ◽  
A Gerald Shaper
Keyword(s):  
Physical Activity ◽  
Risk Factors ◽  
Blood Pressure ◽  
Body Mass Index ◽  
Cardiovascular Risk ◽  
Cardiovascular Risk Factors ◽  
Alcohol Intake ◽  
Blood Lipids ◽  
The Other ◽  
The Relationship

SummaryThe relationship between haematocrit and cardiovascular risk factors, particularly blood pressure and blood lipids, has been examined in detail in a large prospective study of 7735 middle-aged men drawn from general practices in 24 British towns. The analyses are restricted to the 5494 men free of any evidence of ischaemic heart disease at screening.Smoking, body mass index, physical activity, alcohol intake and lung function (FEV1) were factors strongly associated with haematocrit levels independent of each other. Age showed a significant but small independent association with haematocrit. Non-manual workers had slightly higher haematocrit levels than manual workers; this difference increased considerably and became significant after adjustment for the other risk factors. Diabetics showed significantly lower levels of haematocrit than non-diabetics. In the univariate analysis, haematocrit was significantly associated with total serum protein (r = 0*18), cholesterol (r = 0.16), triglyceride (r = 0.15), diastolic blood pressure (r = 0.17) and heart rate (r = 0.14); all at p <0.0001. A weaker but significant association was seen with systolic blood pressure (r = 0.09, p <0.001). These relationships remained significant even after adjustment for age, smoking, body mass index, physical activity, alcohol intake, lung function, presence of diabetes, social class and for each of the other biological variables; the relationship with systolic blood pressure was considerably weakened. No association was seen with blood glucose and HDL-cholesterol. This study has shown significant associations between several lifestyle characteristics and the haematocrit and supports the findings of a significant relationship between the haematocrit and blood lipids and blood pressure. It emphasises the role of the haematocrit in assessing the risk of ischaemic heart disease and stroke in individuals, and the need to take haematocrit levels into account in determining the importance of other cardiovascular risk factors.

Structuralism as a Pamphlet (On the Book by E. Reinert “How Rich CountriesGot Rich... And Why Poor Countries Stay Poor”. 2nd ed.)

2014 ◽  
pp. 147-153
Author(s):  
P. Orekhovsky
Keyword(s):  
Economic Theory ◽  
Economic Development ◽  
Structural Analysis ◽  
Increasing Returns ◽  
The Other ◽  
Static Theory ◽  
Poor Countries ◽  
Historical School ◽  
Socio Economic Development ◽  
The Relationship

The review outlines the connection between E. Reinert’s book and the tradition of structural analysis. The latter allows for the heterogeneity of industries and sectors of the economy, as well as for the effects of increasing and decreasing returns. Unlike the static theory of international trade inherited from the Ricardian analysis of comparative advantage, this approach helps identify the relationship between trade, production, income and population growth. Reinert rehabilitates the “other canon” of economic theory associated with the mercantilist tradition, F. Liszt and the German historical school, as well as a reconside ration of A. Marshall’s analysis of increasing returns. Empirical illustrations given in the book reveal clear parallels with the path of Russian socio-economic development in the last twenty years.

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