With the advent of wireless technology, new tools are available that are intended to enhance students' learning and attitudes. To assess the effectiveness of wireless student response systems in the biology curriculum at New Mexico State University, a combined study of student attitudes and performance was undertaken. A survey of students in six biology courses showed that strong majorities of students had favorable overall impressions of the use of student response systems and also thought that the technology improved their interest in the course, attendance, and understanding of course content. Students in lower-division courses had more strongly positive overall impressions than did students in upper-division courses. To assess the effects of the response systems on student learning, the number of in-class questions was varied within each course throughout the semester. Students' performance was compared on exam questions derived from lectures with low, medium, or high numbers of in-class questions. Increased use of the response systems in lecture had a positive influence on students' performance on exam questions across all six biology courses. Students not only have favorable opinions about the use of student response systems, increased use of these systems increases student learning.
Abstract.Whereas it has been demonstrated that muscle and nonmuscle isoactins are segregated into distinct cytoplasmic domains, the mechanism regulating subcellular sorting is unknown (Herman, 1993a). To reveal whether isoform-specific actin-binding proteins function to coordinate these events, cell extracts derived from motile (Era) versus stationary (Es) cytoplasm were selectively and sequentially fractionated over filamentous isoactin affinity columns prior to elution with a KC1 step gradient. A polypeptide of interest, which binds specifically to/3-actin filament columns, but not to muscle actin columns has been conclusively identified as the ERM family member, ezrin. We studied ezrin-/3 interactions in vitro by passing extracts (Era) over isoactin affinity matrices in the presence of Ca2+-containing versus Ca2+-free buffers, with or without cytochalasin D. Ezrin binds and can be released from/3-actin Sepharose-4B in the presence of Mg2+/EGTA and 100 mM NaC1 (at 4°C and room temperature), but not when affinity fractionation of Em is carried out in the presence of 0.2 mM CaC12 or 2/~M cytochalasin D. N-acetyl-(leucyl)2-norleucinal and E64, two specific inhibitors of the calcium-activated protease, calpain I, protect ezrin binding to B actin in the presence of calcium. Moreover, biochemical analysis of endothelial lysates reveals that a calpain I cleavage product of ezrin emerges when cell locomotion is stimulated in response to monolayer injury. Immunofluorescence analysis of leading lamellae reveals that anti-ezrin and anti-~-actin IgGs can be simultaneously co-localized, extending the results of isoactin affinity fractionation of Em-derived extracts and suggesting that ezrin and B-actin interact in vivo. To test the hypothesis that ezrin binds directly to B-actin, we performed three sets of studies under a wide range of physiological conditions (pH 7.0-8.5) using purified pericyte ezrin and either o~-or B-actin. These included co-sedimentation, isoactin affinity fractionation, and co-immunoprecipitation. Results of these experiments reveal that purified ezrin does not directly bind to ~-actin filaments, either in solution or while isoactins are covalently crosslinked to Sepharose-4B. This is in contrast to our finding that ezrin and ~-actin could be co-immunoprecipitated or co-sedimented from E,~-derived cell lysates. To explore whether calcium transients occur in cellular domains enriched in ezrin and ~-actin, we mapped cellular free calcium in endothelial monolayers crawling in response to injury. Confocal imaging of fluo-3 fluorescence followed by simultaneous double antibody staining reveals a transient rise of free calcium within ezrin-/3-actin-enriched domains in the majority of motile cells bordering the wound edge. These results support the notion that calcium and calpain I modulate ezrin and B-actin interactions during forward protrusion formation.ECE~qT studies indicate that the contractile protein isoforms play distinct roles in facilitating cell function. For the isoactins, there is an emerging ...
A major question in cytokinesis research is the precise architecture of actin and nonmuscle myosin II filaments in the animal cell contractile ring. Superresolution and transmission electron microscopy support an actomyosin organization consistent with the sliding-filament/purse-string model of cytokinesis.
Cytokinesis in animal cells is accomplished in part by an actomyosin contractile ring. Recent work on amphibian, Drosophila, and Caenorhabditis elegans embryos implicates membrane trafficking and delivery as essential for cytokinesis. However, the relative contributions of contractile ring constriction versus membrane insertion to cytokinesis and the temporal relationship between these processes are largely unexplored. Here we monitor secretion of the extracellular matrix protein, hyalin, as a marker for new plasma membrane addition in dividing sea urchin zygotes. We find that new membrane addition occurs specifically in the cleavage furrow late in telophase independent of contractile ring constriction. The directed equatorial deposition of new furrow membrane requires astral microtubules and release of internal stores of Ca 2؉ , but not the presence of a central spindle. Further, cells arrested in M phase do not secrete hyalin, suggesting that mitotic exit is required for new membrane addition. These results demonstrate that astral overlap in equilaterally dividing cells not only serves to specify positioning and contraction of the contractile ring, but also to direct the delivery of new membrane to the furrow as a late, independent event during cytokinesis. T he fundamental mechanics by which chromosomes are segregated into daughter cells during mitosis are highly conserved in eukaryotic cells. The cyclin-dependent kinasemediated assembly of a microtubule-based mitotic spindle, the antagonistic actions of molecular motors, and the presence of a kinetochore-based mitotic checkpoint are common to all plant, animal, and fungal cells (1). In contrast, a variety of strategies are used to effect the physical partitioning of cytoplasm during cytokinesis (2), which has complicated the understanding of cleavage plane determination and daughter cell separation. Recent advances in model organisms, however, have revealed commonalties suggesting that the mechanisms of cytokinesis in diverse systems are more similar than previously appreciated (3). One component of cytokinesis that may be a requirement for both plant and animal cells is the generation of new plasma membrane (4, 5).Daughter cell separation in plant cells is driven by the generation of new cell surface at the cleavage plane. A microtubuleand microfilament-based structure termed the phragmoplast is formed at the spindle midzone that mediates the delivery of membrane vesicles that in turn fuse to form the new cell wall (6). Like plant cells, the mitotic apparatus in animal cells also specifies the cleavage plane, but does so by directing the assembly of an actomyosin contractile ring, which provides the contractile force for furrow ingression (7). The role of membrane addition in cytokinesis in most animal cells, however, is less clear.In large embryonic cells, such as dividing amphibian eggs, the requirement for new membrane addition has been appreciated for some time (8). In these cells, new membrane addition is independent of furrow constriction because inhi...
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