Cargo transport by molecular motor complexes in the crowded cell

The cell requires a high degree of internal organization for its survival. A set of specialized proteins known as molecular motors, are responsible for positioning large molecules and organelles in their correct spatiotemporal location. These proteins must navigate through the crowded cytoplasm as they haul their cargoes to their destination. Although the properties of the individual motors have been studied extensively in vitro, less is known about their functioning inside the cell. Of particular interest is the question of how in vivo opposing forces, e.g. cytoplasmic drag, affect cargo transport. This work presents studies of how cytoplasmic drag forces are involved in cargo transport at various length scales. First, a novel model of centrosome centering in large cells is presented. This model shows that the drag forces experienced by motor-driven cargoes are sufficient to position the large centrosome and associated microtubule aster; however, it raises the question of how these opposing forces affect the function of molecular motors. To address this issue, a combination of biophysical and biochemical tools is used to reveal the average response to drag forces of molecular motors as they haul lipid droplets in Drosophila embryos. A strikingly different response to load is found for the molecular motors kinesin-1 and cytoplasmic dynein. The results here presented validate, for the first time, the applicability of the Force-velocity curves previously measured in vitro for in vivo studies.Physic

Síndrome da tensão pré-menstrual observada em usuárias do ambulatório municipal de saúde da mulher

Many women suffer with Premenstrual Tension Syndrome (STPM) that has symptoms that precede menstruation, causing irritation, anxiety and low self esteem. The STPM affects women in the productive stage causing physical, psychological and social alterations.The aim of the research was to identify the users of an ambulatory health clinic of Tupanciretã, RS. This is a descriptive and exploratory study with qualitative-quantitative approaches. The results provided that women have STPM with different intensity, symptoms range from physical and mental and interfere with daily functioning of women.It was concluded that overall efforts, especially those from health professionals, and through practices which provide communication and health education for women affected by the STPM. In addition to the implementation of actions that provide changing habits, attitudes and behaviors that these women are looking for a better quality of life.Muchas mujeres sufren de Síndrome de Tensión Premenstrual (STPM), que presenta síntomas que anteceden a la menstruación, generando irritación, ansiedad y baja autoestima. El STPM afecta a mujeres en la etapa productiva provocando alteraciones físicas, psíquicas y sociales. El objetivo de la investigación fue identificar y caracterizar a las usuarias de un ambulatorio de salud del municipio de Tupanciretã-RS. Se trata de un estudio descriptivo y exploratorio con abordajes cuali-cuantitativos. Los resultados aportaron que las mujeres poseen STPM con diferente intensidad, los síntomas varían entre los físicos y psíquicos e interfieren en el desempeño cotidiano de las mujeres. Se concluye que es necesario el esfuerzo de los profesionales de salud, por medio de prácticas que proporcionen comunicación y educación en salud en las mujeres afectadas por el STPM. Aparte de la implementación de acciones que prevean cambios de hábitos, actitudes y comportamientos buscando que estas mujeres tengan una mejor calidad de vida. Muitas mulheres sofrem de Síndrome da Tensão Pré-Menstrual (STPM), síndrome que apresenta sintomas precedentes a menstruação, causando irritação, ansiedade e baixa autoestima. A STPM afeta as mulheres causando alterações física, psicológica e social. O objetivo da pesquisa foi identificar e caracterizar as usuárias de um ambulatório municipal de saúde no município de Tupanciretã - RS. Trata-se de um estudo descritivo e exploratório, com abordagem quali - quantitativa. Os resultados denotam que as mulheres têm STPM em diferente intensidade, os sintomas variam entre as mulheres, interferindo a ordem física e emocional. Conclui-se que se faz necessário o esforço dos profissionais de saúde, por meio de práticas que proporcionem comunicação e educação em saúde com as mulheres afetadas pela STPM. Além de ações que preveem mudanças de hábitos, atitudes e comportamentos a fim de que estas mulheres tenham uma melhor qualidade de vida

The green braid : towards an architecture of ecology, economy, and equity / edited by Kim Tanzer and Rafael Longoria.

Includes bibliographical references and index.xvii, 374 pages :Drawn from national design awards published by the Association of Collegiate Schools of Architecture (ACSA), this volume presents the discipline's thinking on sustainability in written, drawn, and built form. Using essays that revise and clarify 20th century architectural thinking, it places sustainability at the centre of architectural design

Cargo Transport by Cytoplasmic Dynein Can Center Embryonic Centrosomes

To complete meiosis II in animal cells, the male DNA material needs to meet the female DNA material contained in the female pronucleus at the egg center, but it is not known how the male pronucleus, deposited by the sperm at the periphery of the cell, finds the cell center in large eggs. Pronucleus centering is an active process that appears to involve microtubules and molecular motors. For small and medium-sized cells, the force required to move the centrosome can arise from either microtubule pushing on the cortex, or cortically-attached dynein pulling on microtubules. However, in large cells, such as the fertilized Xenopus laevis embryo, where microtubules are too long to support pushing forces or they do not reach all boundaries before centrosome centering begins, a different force generating mechanism must exist. Here, we present a centrosome positioning model in which the cytosolic drag experienced by cargoes hauled by cytoplasmic dynein on the sperm aster microtubules can move the centrosome towards the cell’s center. We find that small, fast cargoes (diameter ~100 nm, cargo velocity ~2 µm/s) are sufficient to move the centrosome in the geometry of the Xenopus laevis embryo within the experimentally observed length and time scales.This work was supported in part by the National Science Foundation grant PHY-0957811 to GTS. (www.nsf.gov) The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding was received for this study.PhysicsCellular and Molecular BiologyEmail: [email protected]

Schematic of the geometry of the embryo used in the model and the forces involved.

<p>The embryo has the spherical geometry of that of the early <i>Xenopus laevis</i> embyo with the sperm’s pronucleus and its associated microtubule aster positioned close to the cortex. As cargos are transported by minus-end directed motors towards the centrosome they experience an opposing cytosolic drag force (F_drag, magnified schematic). That force equals the force exerted by the motors on the microtubules and points in opposite directions on the two sides of the centrosome. The net force, F_net, on the centrosome and associated male pronucleus points towards the far cortical side since the microtubules on that side can grow longer and support more vesicles than those on the other side. The net effect is motion of the growing aster towards the cell center.</p

Using centrosome dynamics to study cytosolic loading of molecular motors.

<p>(A)A schematic sketch of a convex-up force-velocity (F–v) relation for a molecular motor shows that the velocity of the motor decreases only slightly up to an opposing load of about one half its stall force then decreases precipitously. A motor hauling a cargo will experience an opposing load from cytosolic drag that determines its speed at the intersection of the load line (dashed) and the F–v curve. When the aster starts moving towards the center, the minus-end motors on the far cortical side will experience a smaller load and speed up (<i>v</i>_v^R) while those on the other side will slow down (<i>v</i>_v^L) (as indicated by the two load lines). For slightly loaded motors, the motor speeds on either side of the centrosome will not differ appreciably, while they will diverge significantly for highly loaded motors. (B) Molecular motors with a concave-up force velocity curve will result in slightly-loaded motors exhibiting a large difference in cargo velocity on either side of the centrosome. Measuring cargo velocities moving along centering aster microtubules can help understand the loading state of the motors if their force-velocity relation is known.</p

Centrosome dynamics as a function of vesicle velocity.

<p>(A) After an initial ramp up, the centrosome velocity keeps increasing at a much smaller rate. As the difference in number of vesicles moving along microtubules in the far and near cortical sides decreases, the centrosome slows down (arrows). Given that slower vesicles experience a smaller drag force, they lead to a slower centrosome. (B) The corresponding position of the centrosome shows that the small, fast-moving vesicles are sufficient to move the centrosome distances comparable to the motion of the centrosome in fertilized <i>Xenopus laevis</i> embryos. Experiments show that the centrosome moves at least 300 µm in 45 minutes; the dashed lines delineate that region. (calculation parameters: 100 microtubules; 100 nm diameter vesicles; viscosity ratio = 3; 2 vesicles/µm; 250 nm/s MT polymerization rate; vesicle velocity as indicated: 2 µm/s (green), 1 µm/s (red), 0.5 µm/s (black) in that order from top to bottom).</p