ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Publication Date: 2014-04-15
    Description: Important processes of living cells, including intracellular transport, cell crawling, contraction, division, and mechanochemical signal transduction, are controlled by cytoskeletal (CSK) dynamics. CSK dynamics can be measured by tracking the motion of CSK-bound particles. Particle motion has been reported to follow a superdiffusive behavior that is believed to arise from ATP-driven intracellular stress fluctuations generated by polymerization processes and motor proteins. The power spectrum of intracellular stress fluctuations has been suggested to decay with 1/2 (Lau et al, Phys Rev Lett 91:198101). Here we report direct measurements of cellular force fluctuations that are transmitted to the extracellular matrix, and compared them with the spontaneous motion of CSK-bound beads. Fibronectin coated fluorescent beads (Ø 1 m) were bound to the CSK of confluent human vascular endothelial cells. Forces transmitted to the extracellular matrix (ECM) were quantified by plating these cells onto a collagen coated elastic polyacrylamide hydrogel, and measuring the gel deformation from the displacement of embedded fluorescent beads (Ø 0.5 m). Bead motion of both CSK-bound and ECM-bound beads were measured with nanometer-resolution and expressed as mean square displacement (MSD). The MSD of both CSK-bound and ECM-bound beads displayed a superdiffusive behavior that was well described by a power law: MSD = a*t^b. Surprisingly, we found an identical power law exponent for both CSK-bound and ECM-bound beads of b = 1.6. This finding suggests that the spontaneous motion of CSK-bound beads is driven by stress fluctuations with a 1/ b+1 power spectrum. This result is consistent with the notion that CSK dynamics and CSK stress fluctuations are closely coupled.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2014-04-15
    Description: Important processes of living cells, including intracellular transport, cell crawling, contraction, division and mechanochemical signal transduction, are controlled by cytoskeletal (CSK) dynamics. Some aspects of CSK dynamics have been studied by following the spontaneous motion of CSK-bound particles. Such particle exhibit a superdiffusive behavior that is believed to arise from random local ATP-driven intracellular force fluctuations generated by polymerization processes and motor proteins. (Lau et al, Phys Rev Lett 91:198101). Here we report simultaneous measurements of spontaneous particle motions and cellular force fluctuations. Human vascular endothelial cells were plated onto collagen coated elastic polyacrylamide hydrogels. Force fluctuations at the basal cell membrane(cell tractions) were computed from the displacements of gel-embedded fluorescent beads. Spontaneous particle motion was measured using fibronectin coated fluorescent beads that were bound to the apicell cell membrane via integrin receptors. Bead motion of both CSK-bound and ECM-bound beads were measured with nanometer-resolution and expressed as mean square displacement (MSD). The MSD of both CSK-bound and ECM-bound beads displayed a superdiffusive behavior that was well described by a power law: MSD = a*t^b. In contradiction to existing theories of stress dissipation within the CSK, we found an identical power law exponent for both CSK-bound and ECM-bound beads of b = 1.6. This finding suggests that the spontaneous motion of CSK-bound beads is driven not by random, local stress fluctuations within a viscoelastic continuum, but rather by large scale stress fluctuations within a CSK network that transmits these stresses with little or no dissipation to the ECM.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2014-06-06
    Description: Emperor penguins (Aptenodytes forsteri Gray) are the only vertebrate species that breed during the Antarctic winter. From the beginning of the breeding season in April until fledging of the chicks in January, emperor penguins rely on the stability of sea (fast) ice. The International Union for Conservation of Nature (IUCN) has recently listed the species as ‘near threatened’ because the habitat of emperor penguins may deteriorate significantly over the coming years with the anticipated changes in sea ice conditions due to climate change. Since 2009, four emperor penguin colonies have been observed on ice shelves, as opposed to sea ice, during the breeding season (Fretwell et al. 2014). This striking change in their breeding behaviour was interpreted as an adaptation of emperor penguins to poor sea ice conditions. Here we report that a large part of the emperor penguin colony at Atka Bay (Dronning Maud Land, Antarctica) moved onto the ice shelf during the 2013 breeding season. This colony has been regularly observed since 1981 but has never before been seen breeding, incubating their eggs, brooding or crèching on the ice shelf. Our observations concur with a recent report, which documented that altered breeding behaviour in emperor penguins has occurred almost simultaneously across Antarctica (Fretwell et al. 2014). Interestingly, the sea ice at Atka Bay has been stable for three consecutive seasons and thus cannot have triggered this change in behaviour. Rather, we present evidence of increased snow accumulation that has greatly improved the accessibility of the ice shelves around Atka Bay, and we discuss additional meteorological factors and local topographical conditions that may have contributed to the shift in breeding location from sea ice onto an ice shelf.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2019-07-17
    Description: For most cell types, adhesion, spreading and tension generation are crucial for cell survival. These processes are strongly influenced by the rigidity of the extracellular matrix: Cells spread more and faster, and generate higher tension on more rigid substrates. We report simulta- neous measurements of cell spreading and traction generation during adhesion of MDA-MB-231 breast carcinoma cells onto collagen coated polyacrylamid gels. The Youngs modulus of the gels was tuned between 1500 (’soft’) and 6000 (’hard’) Pa. The evolution of cell tractions was computed from the gel deformation measured every 30 sec by tracking the displacements of fluorescent beads (ø0.5µm) embedded at the gel surface. As a robust estimate of total force generation, we computed for each cell the elastic strain energy U stored within the gel. As ex- pected, cells generated a higher maximum strain energy U = 1.01pJ) and spread more (A = 6002 ± 961µm2) on harder gels compared to softer gels (U = 0.20pJ, A = 3012 ± 492µm2). When the strain energy vs. time data of individual cells were normalized by spreading area, they collapsed onto a single relationship, regardless of gel stiff- ness. These data extend earlier findings of a proportionality between cell spreading and tension generation (Reinhard-King, Biophys J 2005) and show that individual cells exhibit a constant rate of stress increase during early adhesion events regardless of the substrate rigidity.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2019-07-17
    Description: To withstand the Antarctic cold on open land for more than two months, Emperor penguins are forming densely packed huddles with a hexagonal lattice structure. Video recordings have revealed striking dynamical reorganization processes within those huddles (PLoS One, 6:e20260, 2011), including wave-like patterns, global rotatory motions and abrupt transitions to a disordered state. Here we show that ba- sic aspects of the huddling behavior can be reproduced with simple systems of interacting point particles. For a more realistic modeling, the individual animals are treated as self-driven, information process- ing agents with situation-dependent behavior, similar to simulations of collective swarm behavior in fl ocks and herds. We present a multi- agent simulation in which both the spontaneous huddle formation and the observed wave patterns emerge from simple rules that only encom- pass the interaction between directly neighboring individuals. Our model shows that a collective wave can be triggered by a forward step of any individual within the dense huddle. The group velocity of the resulting wave is dependent only on the reaction times and the step velocity of the animals. By including the mutual adaption of individ- ual body orientations, we present fi rst results on rotary and curved movement patterns.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2019-07-17
    Description: Despite the enormous popularity of penguins, their social behaviour remains poorly understood. Video recordings of penguins and penguin colonies are sporadic, of insufficient resolution and duration, and suffer from camera movements that may be artistically motivated but make them scientifically worthless. Recordings of penguin colonies during the winter months are particularly short in supply. Here we present three different observatories that are able to automatically take time-lapse recording over prolonged time periods under harsh climatic conditions. i) The microbs is a very low cost observatory (~700 US$), capable of recording high-resolution (12 MPix) time-lapse data. It features a water-proof Canon D10 consumer-grade camera that we programmed through a bootable SD-card. The camera is powered by a 40 W solar panel and a 100 Ah 12V battery. The microbs can record up to 32 GB of data (approximately one month at a rate of 1 image/min) before the memory card has to be changed manually. ii) To enable even longer observations at very remote locations where a regular change of the SD-card is not feasible, we designed the Mobile Emperor Penguin Observatory (MEPO). It is equipped with a night vision (b/w) and daylight (color) CCD-sensor. Images are recorded on a solid-state PC with very low energy consumption, or they can be sent via satellite (Inmarsat) that is available on large parts of the Antarctic coast. The observatory is remote-operated through the satellite link to adjust parameters such as image frame rate, to select the images to be sent via satellite or to power the observatory up or down. iii) The Single Penguin Observation & Tracking (SPOT) observatory is used to track the movements of individual penguins over prolonged time periods and count the present number of individual penguins. The observatory consists of a wide-angle (45°) camera and a high-speed (5 images/s) high resolution (11 MPix) camera equipped with a telephoto lens (400-600mm). We deployed several microbs, one MEPO and three SPOT observatory between 2011-13 at Crozet Island, Adelie Land and Atka Bay, respectively, and will present first results.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2019-07-13
    Description: We describe a novel synchronous detection approach to map the transmission of mechanical stresses within the cytoplasm of an adherent cell. Using fluorescent protein-labeled mitochondria or cytoskeletal components as fiducial markers, we measured displacements and computed stresses in the cytoskeleton of a living cell plated on extracellular matrix molecules that arise in response to a small, external localized oscillatory load applied to transmembrane receptors on the apical cell surface. Induced synchronous displacements, stresses, and phase lags were found to be concentrated at sites quite remote from the localized load and were modulated by the preexisting tensile stress (prestress) in the cytoskeleton. Stresses applied at the apical surface also resulted in displacements of focal adhesion sites at the cell base. Cytoskeletal anisotropy was revealed by differential phase lags in X vs. Y directions. Displacements and stresses in the cytoskeleton of a cell plated on poly-L-lysine decayed quickly and were not concentrated at remote sites. These data indicate that mechanical forces are transferred across discrete cytoskeletal elements over long distances through the cytoplasm in the living adherent cell.
    Keywords: Life Sciences (General)
    Type: American journal of physiology. Cell physiology (ISSN 0363-6143); 285; 5; C1082-90
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2019-07-17
    Description: Studies of animal behavior in remote polar regions are essential to understand ecologic change, yet they require significant human and logistic resources. Behavioral data are mostly gathered by tagging single animals, such as penguins and whales. While tagging delivers high-accuracy data for single animals, it cannot be used to study collective behavior in social species due to high costs and the often time-consuming or disturbing tagging process. We present an alternative approach to study animal behavior using automated, remotely operated and energetically independent image acquisition systems. We developed a land-based system for studying penguins, and a sea-based system to study whales. The sea-based system employs a rotating infrared camera (5 rev/s, 360°) for the automatic detection of whales within a radius of up to 3 nautical miles during day and night, and a high-resolution CCD camera equipped with a telephoto lens. Upon detection of a whale in the thermal image, the CCD-camera is automatically pointed at the respective location, and triggered to acquire photos at 5 Hz, allowing species identification up to several miles distance The imaging system is mounted on an active tilt stage to counteract ship movements in heavy seas, which allows to calculate absolute whale positions with an accuracy of ~10%. From the trajectory of an individual whale, likely areas of subsequent surfacing positions are estimated, providing proactive tracing of the whale, which improves the likelyhood of capturing it on photo and and its identification. Automatic whale detection and identification data may then be used to conduct autonomous line transect surveys throughout the cruise. Continuous automatic whale detections during recent expeditions contibuted significantly to the amount of data available for density calculations and habitat suitability modeling. We will present data from three expeditions on RV Polarstern during the years 2009-2011, including several tens of ship-whale encounters. The system will be used during two more expeditions in early 2012, for automatic marine mammal detection, localization and identification purposes. Our land-based system employed a simpler image acquisition and automated analysis technology and was first used to study the collective behavior of Emperor penguins during huddling. The system is capable of simultaneously tracking the positions of more than 1400 huddling emperor penguins. The trajectories revealed that Emperor penguins move collectively in a highly coordinated manner to ensure mobility while at the same time keeping the huddle tightly packed. Every 30–60 seconds, all penguins make small steps, which travel as a wave through the entire huddle. Over time, these small movements lead to large-scale reorganization of the huddle. Moreover, from the high-resolution images is it possible to obtain a precise count of the penguin colony, and to obtain morphometric data from individual penguins to monitor their nutritional state. Thus far, we built five observatories that are currently being shipped to an Adélie penguin (Adélie Land), King penguin (Crozet Island) and Emperor penguin (Atka Bay, Adélie Land) colony, respectively. All three observatories are designed for year-round operations.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2019-07-17
    Description: In polar regions, highly adapted social behavior is crucial for the survival of several species. One prominent example is the huddling behavior of Emperor penguins. To understand how Emperor penguins solve the physical problem of movement in densely packed huddles, we observed an Emperor penguin colony (Atka Bay) with time-lapse imaging and tracked the positions of more than 1400 huddling penguins. The trajectories revealed that Emperor penguins move collectively in a highly coordinated manner to ensure mobility while at the same time keeping the huddle tightly packed. Every 30 - 60 seconds, all penguins make small steps, which travel as a wave through the entire huddle. Over time, these small movements lead to large-scale reorganization of the huddle. Our data show that the dynamics of penguin huddling is governed by intermittency and approach to kinetic arrest in striking analogy with inert non-equilibrium systems. We will also present observations from a different Emperor penguin colony (Adélie Land), an Adélie penguin colony (Adélie Land), and a King penguin colony (Crozet Island).
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2019-07-17
    Description: For Emperor penguins (Aptenodytes forsteri), huddling is the key to survival during the Antarctic winter. Penguins in a huddle are packed so tightly that individual movements become impossible, reminiscent of a jamming transition in compacted colloids. It is crucial, however, that the huddle structure is continuously reorganized to give each penguin a chance to spend sufficient time inside the huddle, compared with time spent on the periphery. Here we show that Emperor penguins move collectively in a highly coordinated manner to ensure mobility while at the same time keeping the huddle packed. Every 30–60 seconds, all penguins make small steps that travel as a wave through the entire huddle. Over time, these small movements lead to large-scale reorganization of the huddle. Our data show that the dynamics of penguin huddling is governed by intermittency and approach to kinetic arrest in striking analogy with inert non-equilibrium systems, including soft glasses and colloids.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...