Reinforcement versus Fluidization in Cytoskeletal Mechanoresponsiveness

Every adherent eukaryotic cell exerts appreciable traction forces upon its substrate. Moreover, every resident cell within the heart, great vessels, bladder, gut or lung routinely experiences large periodic stretches. As an acute response to such stretches the cytoskeleton can stiffen, increase traction forces and reinforce, as reported by some, or can soften and fluidize, as reported more recently by our laboratory, but in any given circumstance it remains unknown which response might prevail or why. Using a novel nanotechnology, we show here that in loading conditions expected in most physiological circumstances the localized reinforcement response fails to scale up to the level of homogeneous cell stretch; fluidization trumps reinforcement. Whereas the reinforcement response is known to be mediated by upstream mechanosensing and downstream signaling, results presented here show the fluidization response to be altogether novel: it is a direct physical effect of mechanical force acting upon a structural lattice that is soft and fragile. Cytoskeletal softness and fragility, we argue, is consistent with early evolutionary adaptations of the eukaryotic cell to material properties of a soft inert microenvironment

Fluidization and Resolidification of the Human Bladder Smooth Muscle Cell in Response to Transient Stretch

Background: Cells resident in certain hollow organs are subjected routinely to large transient stretches, including every adherent cell resident in lungs, heart, great vessels, gut, and bladder. We have shown recently that in response to a transient stretch the adherent eukaryotic cell promptly fluidizes and then gradually resolidifies, but mechanism is not yet understood. Principal Findings: In the isolated human bladder smooth muscle cell, here we applied a 10% transient stretch while measuring cell traction forces, elastic modulus, F-actin imaging and the F-actin/G-actin ratio. Immediately after a transient stretch, F-actin levels and cell stiffness were lower by about 50%, and traction forces were lower by about 70%, both indicative of prompt fluidization. Within 5min, F-actin levels recovered completely, cell stiffness recovered by about 90%, and traction forces recovered by about 60%, all indicative of resolidification. The extent of the fluidization response was uninfluenced by a variety of signaling inhibitors, and, surprisingly, was localized to the unstretch phase of the stretch-unstretch maneuver in a manner suggestive of cytoskeletal catch bonds. When we applied an “unstretch-restretch” (transient compression), rather than a “stretch-unstretch” (transient stretch), the cell did not fluidize and the actin network did not depolymerize. Conclusions: Taken together, these results implicate extremely rapid actin disassembly in the fluidization response, and slow actin reassembly in the resolidification response. In the bladder smooth muscle cell, the fluidization response to transient stretch occurs not through signaling pathways, but rather through release of increased tensile forces that drive acute disassociation of actin

Detecting people and content in educational videos

Thesis: M. Eng. in Computer Science and Engineering, Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 61-65).There are thousands of hours of educational content on the Internet, with services like edX, Coursera, Berkeley WebCasts, and others offering hundreds of courses to hundreds of thousands of learners. Consequently, researchers are interested in the effectiveness of video learning. While educational videos vary, they share two common attributes: people and textual content. People are presenting content to learners in the form of text, graphs, charts, tables, and diagrams. With an annotation of people and textual content in an educational video, researchers can study the relationship between video learning and retention. This thesis presents EdVidParse, an automatic tool that takes an educational video and annotates it with bounding boxes around the people and textual content. EdVidParse uses internal features from deep convolutional neural networks to estimate the bounding boxes, achieving a 0.43 AP score on a test set. Three applications of EdVidParse, including identifying the video type, identifying people and textual content for interface design, and removing a person from a picture-in-picture video are presented. EdVidParse provides an easy interface for identifying people and textual content inside educational videos for use in video annotation, interface design, and video reconfiguration.by Michele Pratusevich.M. Eng. in Computer Science and Engineerin

On the role of general trauma in the development of endocarditisВо врачебной экспертизе особое место занимает вопрос о значении травмы в происхождении заболеваний сердца.

In medical expertise, a special place is occupied by the question of the importance of trauma in the origin of heart disease.</jats:p

Factors shaping the confocal image of the calcium spark in cardiac muscle cells

The interpretation of confocal line-scan images of local [Ca2+]i transients (such as Ca2+ sparks in cardiac muscle) is complicated by uncertainties in the position of the origin of the Ca2+ spark (relative to the scan line) and by the dynamics of Ca(2+)-dye interactions. An investigation of the effects of these complications modeled the release, diffusion, binding, and uptake of Ca2+ in cardiac cells (producing a theoretical Ca2+ spark) and image formation in a confocal microscope (after measurement of its point-spread function) and simulated line-scan images of a theoretical Ca2+ spark (when it was viewed from all possible positions relative to the scan line). In line-scan images, Ca2+ sparks that arose in a different optical section or with the site of origin displaced laterally from the scan line appeared attenuated, whereas their rise times slowed down only slightly. These results indicate that even if all Ca2+ sparks are perfectly identical events, except for their site of origin, there will be an apparent variation in the amplitude and other characteristics of Ca2+ sparks as measured from confocal line-scan images. The frequency distributions of the kinetic parameters (i.e., peak amplitude, rise time, fall time) of Ca2+ sparks were calculated for repetitive registration of stereotyped Ca2+ sparks in two experimental situations: 1) random position of the scan line relative to possible SR Ca(2+)-release sites and 2) fixed position of the scan line going through a set of possible SR Ca(2+)-release sites. The effects of noise were incorporated into the model, and a visibility function was proposed to account for the subjective factors that may be involved in the evaluation of Ca(2+)-spark image parameters from noisy experimental recordings. The mean value of the resulting amplitude distributions underestimates the brightness of in-focus Ca2+ sparks because large numbers of out-of-focus Ca2+ sparks are detected (as small Ca2+ sparks). The distribution of peak amplitudes may split into more than one subpopulation even when one is viewing stereotyped Ca2+ sparks because of the discrete locations of possible SR Ca(2+)-release sites in mammalian ventricular heart cells