Kinetic persistence of cruciform structures in reconstituted minichromosomes

Cruciforms persist in reconstituted minichromosomes, as revealed by cleavage with specific nucleases and hybridization with synthetic oligonucleotides. Relaxation by topoisomerase I suggests that cruciforms are located mainly on internucleosomal DNA and that their persistence on minichromosomes may be due to kinetic effects. The analysis of the kinetic behaviour of cruciforms in minichromosomes shows a definite velocity of reabsorption with respect to stable cruciforms in supercoiled naked DNA. An explanation based on suppression of the untwisting of linker DNA due to adjacent nucleosomes is proposed.     

Behavior of fish predators and their prey: habitat choice between open water and dense vegetation

Synopsis Behavior of largemouth bass, Micropterus salmoides, and northern pike, Esox lucius, foraging on fathead minnows, Pimephales promelas, or bluegills, Lepomis macrochirus, was quantified in pools with 50% cover (half the pool had artificial stems at a density of 1000 stems m⁻²). Both predators spent most of their time in the vegetation. Largemouth bass searched for bluegills and ambushed minnows, whereas the relatively immobile northern pike ambushed all prey. Minnows were closer to predators and were captured more frequently than bluegills. Even when minnows dispersed, they moved continually and eventually wandered within striking distance of a predator. Bluegills dispersed in the cover with predators. Bass captured the few bluegills that strayed into the open and pike captured those that approached too closely in the cover. The ability of predators to capture prey while residing in habitats containing patches of dense cover may explain their residence in areas often considered to be poor ones for foraging. The unit is sponsored jointly by the United States Fish and Wildlife Service, Ohio Department of NaturalResources, The Ohio State University, and the Wildlife Management Institute     

An analysis of the role of actin during pollen activation leading to germination in pear (Pyrus communis L.): treatment with cytochalasin D

Summary Major stages of actin organization during activation leading to germination of pear (Pyrus communis L.) pollen were disrupted by treatment with 5 g/ml cytochalasin D (CD), and the effects of the drug were monitored with rhodamine-phalloidin staining. CD induced the formation of granules or short rods in the place of the filamentous arrays that occur in normally developing pollen. Filamentous arrays, however, returned upon removal of CD. Pollen incubated directly in CD showed a gradual disappearance of circular actin profiles and their replacement by either granules or, less frequently, short rods. These granules and rods initially had a random distribution in the cell, but with time in CD they became localized at one of the three germination apertures. Pollen was also allowed to reach three stages of microfilament (MF) organization (initial fibrillar arrays, interapertural MFs, and MFs confined beneath a single aperture) prior to being continously exposed to CD. After CD treatment, germination was blocked and the number of cells containing short rods increased, but movement of actin to a single aperture continued. Finally, when pollen at different stages of MF organization was treated with a CD pulse and then transferred to drug-free medium, germination was delayed regardless of the stage of MF organization at the time of treatment. The results indicate that an uninterrupted progression of actin organization is essential for pollen germination, but that movement of actin in the cell is CD-insensitive.     

Alpha Band Cortico-Muscular Coherence Occurs in Healthy Individuals during Mechanically-Induced Tremor

The present work aimed at investigating the effects of mechanically amplified tremor on cortico-muscular coherence (CMC) in the alpha band. The study of CMC in this specific band is of particular interest because this coherence is usually absent in healthy individuals and it is an aberrant feature in patients affected by pathological tremors; understanding its mechanisms is therefore important. Thirteen healthy volunteers (23±4 years) performed elbow flexor sustained contractions both against a spring load and in isometric conditions at 20% of maximal voluntary isometric contraction (MVC). Spring stiffness was selected to induce instability in the stretch reflex servo loop. 64 EEG channels, surface EMG from the biceps brachii muscle and force were simultaneously recorded. Contractions against the spring resulted in greater fluctuations of the force signal and EMG amplitude compared to isometric conditions (p<.05). During isometric contractions CMC was systematically found in the beta band and sporadically observed in the alpha band. However, during the contractions against the spring load, CMC in the alpha band was observed in 12 out of 13 volunteers. Partial directed coherence (PDC) revealed an increased information flow in the EMG to EEG direction in the alpha band (p<.05). Therefore, coherence in the alpha band between the sensory-motor cortex and the biceps brachii muscle can be systematically induced in healthy individuals by mechanically amplifying tremor. The increased information flow in the EMG to EEG direction may reflect enhanced afferent activity from the muscle spindles. These results may contribute to the understanding of the presence of alpha band CMC in tremor related pathologies by suggesting that the origin of this phenomenon may not only be at cortical level but may also be affected by spinal circuit loops.     

Applications of stereology to the mechanics of soft tissues

Quantification of microstructure in conjunction with mechanical testing and modeling may provide new insight into problems of soft tissue mechanics with potential clinical significance. Some general observations concerning this as well as brief discussions of specif examples are presented.     

Neuroendocrine control of thymic hormonal production. II. Stimulatory effects of endogenous opioids on thymulin production by cultured human and murine thymic epithelial cells

Data have now accumulated to strongly demonstrate that several neuropeptides, including endogenous opioids, can have immunomodulatory functions. Most of the studies have so far focused on the direct action of these substances on lymphocytes. We decided to investigate whether thymic epithelial cells (TEC) - the major component of the thymic microenvironment - could also be modulated by endogenous opioids. Primary cultures of human and murine TEC were subjected to several opioids (alpha-beta- or gamma-endorphins, as well as met- or leuenkephalins) applied in concentrations ranging from 10(-6) to 10(-9) M. On the following days we measured the levels of thymulin (a chemically-defined thymic hormone known to stimulate some steps of T-cell differentiation) in the culture supernatants, as well as the numbers of thymulin containing cells, evaluated by immunofluorescence with an anti-thymulin monoclonal antibody. After treatment of TEC cultures with beta-endorphin or leu-enkephalin a significant increase in the levels of thymulin in the culture media was observed, paralleled by a rise in the percentage of thymulin containing cells. In addition, this stimulatory effect was dose-dependent. Preincubation of the opioids with the specific antibodies abrogated the opioid-induced stimulatory effect on TEC. Moreover, naloxone, an opioid receptor antagonist, blocked the effect of beta-endorphin on thymulin production, suggesting that the effect of this neuropeptide on epithelial cells was mediated by an opioid receptor. Importantly, no effect on thymulin production was observed with the other opioids used, whatever the dose. These results suggest that, at least in vitro, beta-endorphin and leu-enkephalin stimulate the hormonal function of the thymic epithelium. These findings lead to the general concept that the modulatory role of endogenous opioids on the immune system is not restricted to lymphocytes but can also take place at the level of cells belonging to T-cell differentiating microenvironments.     

Contribution of Genome-Wide Association Studies to Scientific Research: A Pragmatic Approach to Evaluate Their Impact

The factual value of genome-wide association studies (GWAS) for the understanding of multifactorial diseases is a matter of intense debate. Practical consequences for the development of more effective therapies do not seem to be around the corner. Here we propose a pragmatic and objective evaluation of how much new biology is arising from these studies, with particular attention to the information that can help prioritize therapeutic targets. We chose multiple sclerosis (MS) as a paradigm disease and assumed that, in pre-GWAS candidate-gene studies, the knowledge behind the choice of each gene reflected the understanding of the disease prior to the advent of GWAS. Importantly, this knowledge was based mainly on non-genetic, phenotypic grounds. We performed single-gene and pathway-oriented comparisons of old and new knowledge in MS by confronting an unbiased list of candidate genes in pre-GWAS association studies with those genes exceeding the genome-wide significance threshold in GWAS published from 2007 on. At the single gene level, the majority (94 out of 125) of GWAS-discovered variants had never been contemplated as plausible candidates in pre-GWAS association studies. The 31 genes that were present in both pre- and post-GWAS lists may be of particular interest in that they represent disease-associated variants whose pathogenetic relevance is supported at the phenotypic level (i.e. the phenotypic information that steered their selection as candidate genes in pre-GWAS association studies). As such they represent attractive therapeutic targets. Interestingly, our analysis shows that some of these variants are targets of pharmacologically active compounds, including drugs that are already registered for human use. Compared with the above single-gene analysis, at the pathway level GWAS results appear more coherent with previous knowledge, reinforcing some of the current views on MS pathogenesis and related therapeutic research. This study presents a pragmatic approach that helps interpret and exploit GWAS knowledge.     

ARGoS: a modular, parallel, multi-engine simulator for multi-robot systems

We present a novel multi-robot simulator named ARGoS. ARGoS is designed to simulate complex experiments involving large swarms of robots of different types. ARGoS is the first multi-robot simulator that is at the same time both efficient (fast performance with many robots) and flexible (highly customizable for specific experiments). Novel design choices in ARGoS have enabled this breakthrough. First, in ARGoS, it is possible to partition the simulated space into multiple sub-spaces, managed by different physics engines running in parallel. Second, ARGoS?? architecture is multi-threaded, thus designed to optimize the usage of modern multi-core CPUs. Finally, the architecture of ARGoS is highly modular, enabling easy addition of custom features and appropriate allocation of computational resources. We assess the efficiency of ARGoS and showcase its flexibility with targeted experiments. Experimental results demonstrate that simulation run-time increases linearly with the number of robots. A 2D-dynamics simulation of 10,000 e-puck robots can be performed in 60?% of the time taken by the corresponding real-world experiment. We show how ARGoS can be extended to suit the needs of an experiment in which custom functionality is necessary to achieve sufficient simulation accuracy. ARGoS is open source software licensed under GPL3 and is downloadable free of charge.