Cytoskeletal changes during neurogenesis in cultures of avain neural crest cells

Neural crest cells are motile and mitotic, whereas their neuronal derivatives are terminally post-mitotic and consist of stationary cell body from which processes grow. The present study documents changes in the cytoskeleton that occur during neurogenesis in cultures of avain neural crest cells. The undifferentiated neural crest cells contain dense bundles of actin filaments throughout their cytoplasm, and a splayed array of microtubules attached to the centrosome. In newly differentiating neurons, the actin bundles are disrupted and most of the remaining actin filaments are reorganized into a cortical layer underlying the plasma membrane of the cell body and processes. Microtubules are more abundant in newly-differentiating neurons than in the undifferentiated cells, and individual microtubules can be seen dissociated from the centrosome. Neuron-specific beta-III tubulin appears in some crest cells prior to cessation of motility and cell division, and expression increases with total microtubule levels during neurogenesis. To investigate how these early cytoskeletal changes might contribute to alterations in morphology during neurogenesis, we have disrupted the cytoskeleton with pharmacologic agents. Microfilament disruption by cytochalasin immediately arrests the movement of neural crest cells and causes them to round-up, but does not significantly change the morphology of the immature neurons. Microtubule depolymerization by nocodazole slows the movement of undifferentiated cells and causes retraction of processes extended by the immature neurons. These results suggest that changes in the actin and microtubule arrays within neural crest cells govern distinct aspects of their morphogenesis into neurons.     

On higher structures

In this paper, we discuss various philosophical aspects of the hyperstructure concept extending networks and higher categories. By this discussion, we hope to pave the way for applications and further developments of the mathematical theory of hyperstructures.     

Mutations Closer to the Active Site Improve the Promiscuous Aldolase Activity of 4‐Oxalocrotonate Tautomerase More Effectively than Distant Mutations

The enzyme 4‐oxalocrotonate tautomerase (4‐OT), which catalyzes enol–keto tautomerization as part of a degradative pathway for aromatic hydrocarbons, promiscuously catalyzes various carbon–carbon bond‐forming reactions. These include the aldol condensation of acetaldehyde with benzaldehyde to yield cinnamaldehyde. Here, we demonstrate that 4‐OT can be engineered into a more efficient aldolase for this condensation reaction, with a >5000‐fold improvement in catalytic efficiency (k_cat/K_m) and a >10⁷‐fold change in reaction specificity, by exploring small libraries in which only “hotspots” are varied. The hotspots were identified by systematic mutagenesis (covering each residue), followed by a screen for single mutations that give a strong improvement in the desired aldolase activity. All beneficial mutations were near the active site of 4‐OT, thus underpinning the notion that new catalytic activities of a promiscuous enzyme are more effectively enhanced by mutations close to the active site.     

The impact of atmospheric stability on the near‐surface wind over sea in storm conditions

We study the influence of boundary layer stability on the near‐surface wind speed, especially for high‐wind conditions. An analysis of the wind speed ratio between two vertical levels observed at tall masts in the North Sea and The Netherlands demonstrates that over sea non‐neutral conditions commonly occur, even when the 10 m wind speed is 7 Bft or higher (at least 13.9 ms^?1). Over land, stability conditions are always close to neutral for these strong wind conditions. This is because over land, large vertical temperature differences are rare in these conditions. An analysis of 30 years of station data shows that even in storm conditions the ratio of the 10 m wind speed between sea and land depends systematically on the difference between the air temperature and the sea surface temperature. The observational results are reproduced by HARMONIE, a state‐of‐the‐art Numerical Weather Prediction model, although the impact of stability is smaller than in the observations. A model sensitivity analysis for a severe storm shows that the near‐surface wind speed over sea can vary by 10% depending on the difference between the air temperature and the sea surface temperature. The results presented in this study indicate that even in conditions that are usually classified as ‘(near) neutral’, small variations in stability may have a significant impact on the wind profile. They also indicate that for high wind speeds, the sea‐to‐land wind speed ratio is dominated by the stability over sea as in these conditions the stability over land is close to neutral. Copyright © 2015 John Wiley & Sons, Ltd.     

Strategies for studying microtubule transport in the neuron

Microtubules are prominent cytoskeletal elements within the neuron. They are essential for the differentiation, growth, and maintenance of axons and dendrites. The microtubules within each type of process have a distinct pattern of organization, and these distinct patterns result in many of the morphological and structural features that distinguish axons and dendrites from one another. There are a number of challenges that must be met in order for the neuron to establish the microtubule arrays of axons and dendrites. One attractive model invokes the active transport of microtubules from the cell body of the neuron into and down these processes. In support of this model, specific motor proteins have now been identified within neurons that have the necessary properties to transport microtubules into developing axons and dendrites with the appropriate orientation for each type of process. An important goal is to develop microscopic methods that permit the visualization of microtubule transport within different regions of the neuron. To date, achieving this goal has met with mixed success, probably as a result of the geometry of the neuron and the inherent complexity of the neuronal microtubule arrays. While some approaches have failed to reveal microtubule transport, other more recent approaches have proven successful. These approaches provide strong visual support for a model based on microtubule transport, and provide hope that future approaches can provide even clearer demonstrations of this transport.     

When prevention promotes creativity: The role of mood, regulatory focus, and regulatory closure.

Promotion-focused states generally boost creativity because they associate with enhanced activation and cognitive flexibility. With regard to prevention-focused states, research evidence is less consistent, with some findings suggesting prevention-focused states promote creativity and other findings pointing to no or even negative effects. We proposed and tested the hypothesis that whether prevention-focused states boost creativity depends on regulatory closure (whether a goal is fulfilled or not). We predicted that prevention-focused states that activate the individual (unfulfilled prevention goals, fear) would lead to similar levels of creativity as promotion-focused states but that prevention-focused states that deactivate (closed prevention goals, relief) would lead to lower levels of creativity. Moreover, we predicted that this effect would be mediated by feelings of activation. Predictions were tested in 3 studies on creative insights and 1 on original ideation. Results supported predictions. Implications for self-regulation, motivation, mood, and creativity are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Self‐Assembly of Ferromagnetic Organic–Inorganic Perovskite‐Like Films

Perovskite‐based organic–inorganic hybrids hold great potential as active layers in electronics or optoelectronics or as components of biosensors. However, many of these applications require thin films grown with good control over structure and thickness—a major challenge that needs to be addressed. The work presented here is an effort towards this goal and concerns the layer‐by‐layer deposition at ambient conditions of ferromagnetic organic–inorganic hybrids consisting of alternating CuCl₄‐octahedra and organic layers. The Langmuir‐Blodgett technique used to assemble these structures provides intrinsic control over the molecular organization and film thickness down to the molecular level. Magnetic characterization reveals that the coercive field for these thin films is larger than that for solution‐grown layered bulk crystals. The strategy presented here suggests a promising cost effective route to facilitate the excellently controlled growth of sophisticated materials on a wide variety of substrates that have properties relevant for the high density storage media and spintronic devices.