Effects of plasma membrane cholesterol level and cytoskeleton F-actin on cell protrusion mechanics.

Protrusions are deformations that form at the surface of living cells during biological activities such as cell migration. Using combined optical tweezers and fluorescent microscopy, we quantified the mechanical properties of protrusions in adherent human embryonic kidney cells in response to application of an external force at the cell surface. The mechanical properties of protrusions were analyzed by obtaining the associated force-length plots during protrusion formation, and force relaxation at constant length. Protrusion mechanics were interpretable by a standard linear solid (Kelvin) model, consisting of two stiffness parameters, k0 and k1 (with k0>k1), and a viscous coefficient. While both stiffness parameters contribute to the time-dependant mechanical behavior of the protrusions, k0 and k1 in particular dominated the early and late stages of the protrusion formation and elongation process, respectively. Lowering the membrane cholesterol content by 25% increased the k0 stiffness by 74%, and shortened the protrusion length by almost half. Enhancement of membrane cholesterol content by nearly two-fold increased the protrusion length by 30%, and decreased the k0 stiffness by nearly two-and-half-fold as compared with control cells. Cytoskeleton integrity was found to make a major contribution to protrusion mechanics as evidenced by the effects of F-actin disruption on the resulting mechanical parameters. Viscoelastic behavior of protrusions was further characterized by hysteresis and force relaxation after formation. The results of this study elucidate the coordination of plasma membrane composition and cytoskeleton during protrusion formation

Insight Problem Solving: A Critical Examination of the Possibility of Formal Theory

This paper provides a critical examination of the current state and future possibility of formal cognitive theory for insight problem solving and its associated “aha!” experience. Insight problems are contrasted with move problems, which have been formally defined and studied extensively by cognitive psychologists since the pioneering work of Alan Newell and Herbert Simon. To facilitate our discussion, a number of classical brainteasers are presented along with their solutions and some conclusions derived from observing the behavior of many students trying to solve them. Some of these problems are interesting in their own right, and many of them have not been discussed before in the psychological literature. The main purpose of presenting the brainteasers is to assist in discussing the status of formal cognitive theory for insight problem solving, which is argued to be considerably weaker than that found in other areas of higher cognition such as human memory, decision-making, categorization, and perception. We discuss theoretical barriers that have plagued the development of successful formal theory for insight problem solving. A few suggestions are made that might serve to advance the field

Photoperiodic Adaptation To Latitude In Xanthium Strumarium

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141446/1/ajb206837.pd

How Low Can You Go? The Consequences of Zero Tolerance

Establishing tolerance levels for the presence of unwanted materials that may inadvertently become co-mingled with products that are acceptable in markets is a problem for regulators that requires arbitrary lines in the sand to be drawn. While the degree of tolerance is ultimately an arbitrary value -- because the full information necessary to make a non-arbitrary decision is never forthcoming -- decision making can be informed by theory, existing information, and where gaps in information lie. Where tolerances have been established that do not appear to have been informed, they should be re-examined if for no other reason than they may impose unnecessary costs on society. Zero tolerance has been imposed by regulators in a number of jurisdictions for unwanted materials that could co-mingle with products acceptable in the market. One such case is the European Union's (EU) policy of zero tolerance for co-mingling of unapproved genetically modified (GM) materials with agri-food products. This article uses two case studies related to the regulation of GM materials in the EU to examine the implications of zero tolerance. While the topic of the regulation of modern biotechnology has been the subject of much debate in the EU and globally, there appears to be little discussion of zero tolerance. Given that zero tolerance imposes considerable externalities on non-EU agri-food sectors as well as in the EU itself, it may be time to re-examine zero tolerance in an informed way

Anisotropic Small-Polaron Hopping In W:Bivo4 Single Crystals

DC electrical conductivity, Seebeck and Hall coefficients are measured between 300 and 450 K on single crystals of monoclinic bismuth vanadate that are doped n-type with 0.3% tungsten donors (W:BiVO4). Strongly activated small-polaron hopping is implied by the activation energies of the Arrhenius conductivities (about 300 meV) greatly exceeding the energies characterizing the falls of the Seebeck coefficients' magnitudes with increasing temperature (about 50 meV). Small-polaron hopping is further evidenced by the measured Hall mobility in the ab-plane (10(-1) cm(2) V-1 s(-1) at 300 K) being larger and much less strongly activated than the deduced drift mobility (about 5 x 10(-5) cm(2) V-1 s(-1) at 300 K). The conductivity and n-type Seebeck coefficient is found to be anisotropic with the conductivity larger and the Seebeck coefficient's magnitude smaller and less temperature dependent for motion within the ab-plane than that in the c-direction. These anisotropies are addressed by considering highly anisotropic next-nearest-neighbor (approximate to 5 angstrom) transfers in addition to the somewhat shorter (approximate to 4 angstrom), nearly isotropic nearest-neighbor transfers. (C) 2015 AIP Publishing LLC.U.S. Department of Energy (DOE), DE-FG02-09ER16119Welch Foundation Grant F-1436Hemphill-Gilmore Endowed FellowshipNSF MIRT DMR 1122603Chemical EngineeringTexas Materials InstituteChemistr

Project-Based Learning (PBL) With Virtual Mediations And Computer Tools In An Animal Genetics Course In An Animal Science Program

The project-based learning (PBL) strategy, supported by virtual mediations and computer tools, is an effective method of learning complex subjects based on the use of problems as a starting point for the acquisition or reinforcement of knowledge. In this study, it is proposed to adapt the methodology and approach of PBL to use it as a method of approaching all the curricular contents of the subject Animal Genetics, of the Animal Science programme of the University of Sucre-Colombia. The strategy was developed in the time allotted for the course and was applied to 32 students. The degree of familiarization, academic productivity, asynchronous mediation through e-mail, spreadsheet mastery and appreciation of the methodology implemented were determined. The results showed that 100% of the students were unaware of the application of the strategy, initially showing fears at the beginning of the activity. On analyzing the reports submitted throughout the semester, it was found that 50.0% of the students achieved an average mark of 4.2±0.14, 40.6% achieved an average mark of 3.70±0.09 and only 9.4% obtained a failing mark. 55.2% of the students who achieved a passing grade had an average of more than 4.0 and 45.8% of the students were in the range 3.0- 3.9. The products delivered and the degree of completion were influenced by the degree of mastery of the spreadsheet and the level of email participation recorded. It was found that the learning strategy generated motivation in the students, reflected in the fulfilment of the goals and objectives set at the beginning of the course, and increased student-teacher interaction

Microarrays Reveal Early Transcriptional Events during the Termination of Larval Diapause in Natural Populations of the Mosquito, Wyeomyia smithii

overwinters in a larval diapause that is initiated, maintained and terminated by day length (photoperiod). We use a forward genetic approach to investigate transcriptional events involved in the termination of diapause following exposure to long-days. is up-regulated under long-day response conditions, is located under a QTL for critical photoperiod and is associated with critical photoperiod after 25 generations of recombination from a cross between extreme phenotypes. as a gene either involved in the photoperiodic switch mechanism or very tightly linked to a gene that is. We conclude that continued forward genetic approaches will be central to understanding not only the molecular basis of photoperiodism and diapause, but also the evolutionary potential of temperate and polar animal populations when confronted with rapid climate change

The Properties of the local Interstellar Medium and the Interaction of the Stellar Winds of epsilon Indi and lambda Andromedae with the Interstellar Environment

We present new observations of the Ly alpha lines of Epsilon Indi (K5 5) and A Andromedae (G8 4-3 + ?) These data were obtained by the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. Analysis of the interstellar H 1 and D 1 absorption lines reveals that the velocities and temperatures inferred from the H 1 lines are inconsistent with the parameters inferred from the D 1 lines, unless the H 1 absorption is assumed to be produced by two absorption components. One absorption component is produced by interstellar material. For both lines of sight observed, the velocity of this component is consistent with the velocity predicted by the local flow vector. For the Epsilon Indi data, the large velocity separation between the stellar emission and the interstellar absorption allows us to measure the H 1 column density independent of the shape of the intrinsic stellar Ly alpha profile. This approach permits us to quote an accurate column density and to assess its uncertainty with far more confidence than in previous analyses, for which the errors were dominated by uncertainties in the assumed stellar profiles