Cycling aggregation patterns of cytoplasmic F-actin coordinated with oscillating tension force generation

Isometric contracting protoplasmic veins of Physarum polycephalum show cycling patterns of cytoplasmic F-actin, dependent on their oscillating contraction behaviour (minute rhythms). The process of fibrillogenesis represents a parallel arrangement of F-actin chains ("plasma filaments, microfilaments") during the isometric contraction phase. A part of the results of the present work corroborates previous results on stretch-activated veins which showed that the fibrillar form of F-actin reflects the isometric contracted state. During isometric relaxation phase, a disaggregation of the fibrillar pattern takes place and is accompanied by a deparallelisation of F-actin chains. Therefore, the isometric relaxed state of cytoplasmic actomyosin is non-fibrillar in nature. Thus, the morphologically detectable fibrillar form of cytoplasmic actomyosin, according to physiological interpretation, is solely representative of the isometric contracted state. The question whether assembly-disassembly processes, e.g. G equilibrium F-actin-transformation, play a role in the contraction-relaxation cycle is discussed.     

Dynein and dynactin are localized to astral microtubules and at cortical sites in mitotic epithelial cells

The mitotic spindle is often positioned in a characteristic location during development, for example to enable the proper segregation of developmental determinants [1,2]. When epithelial cells divide, the mitotic spindle is often positioned parallel to the plane of the epithelium, so that both daughter cells contribute to the epithelium [3]. The mechanisms by which mitotic spindles are positioned have not been characterized in great detail, but evidence is accumulating that in some systems the dynein-dynactin microtubule motor complex plays a role [4-6]. Dynein has yet not been localized to cortical sites where it could bind to microtubules and exert a force that might orient the mitotic spindle, however [7,8]. Here, we report that in mitotic polarized epithelial cells, the dynein-dynactin complex accumulates, from prometaphase onwards, along astral microtubules and at cortical spots, into which many of the astral microtubules dock. The spots are assembled at the lateral plasma membrane, in the region below the tight junctions. Their formation is inhibited by cytochalasin D, and under these conditions the spindles do not orient properly. This novel localization of the dynein-dynactin complex is consistent with a role for the complex in the positioning of the mitotic spindle. We also show that, during prophase, the motor complex colocalizes with the nuclear envelope, consistent with it having a role in separating the centrosomes that are associated with the nuclear envelope.     

Call to molecular arms

In a prospective study, cultures were obtained of all intravascular catheters removed from children in an intensive care unit. Of 366 catheters removed from 217 children, 110 (30%) were found to be colonized, most commonly with coagulase-negative staphylococci. Despite the high rate of colonization, there were only nine instances (2%) of catheter-related bacteremia.     

Microbial contamination of radionuclide generators

Technetium-99m generators were grossly contaminted using 5 different strains of microorganisms. Elution of the generators showed that the number of microorganisms was reduced by a factor of 10(4)-10(6). There were no indications that the generators would support bacterial growth. It is concluded that it would be acceptable from a microbiologic point of view to omit autoclaving and membrane filtration of the final product provided that proper aseptic techniques are applied.     

Myosin motors with artificial lever arms

The myosin head consists of a globular catalytic domain and a light chain binding domain (LCBD). The coupling efficiency between ATP hydrolysis and myosin-induced actin movement is known to decline as the LCBD is truncated or destabilized. However, it was not clear whether the observed alteration in the production of force and movement reflects only the mechanical changes to the length of the LCBD or whether these changes also affect the kinetic properties of the catalytic domain. Here we show that replacement of the LCBD with genetically engineered domains of similar rigidity and dimensions produces functional molecular motors with unchanged kinetic properties. The resulting single-chain, single-headed motors were produced in Dictyostelium discoideum and obtained after purification from a standard peptone-based growth medium at levels of up to 12 mg/l. Their actin motility properties are similar or greater than those of native myosin. Rates of 2.5 and 3.3 microm/s were observed for motor domains fused to one or two of these domains, respectively. Their kinetic and functional similarity to the extensively studied myosin subfragment 1 (S1) and their accessibility to molecular genetic approaches makes these simple constructs ideal models for the investigation of chemo-mechanical coupling in the myosin motor.     

How do octopuses use their arms?

A rat PAC library was constructed in the vector pPAC4 from genomic DNA isolated from female Brown Norway rats. This library consists of 215,409 clones arrayed in 614,384-well microtiter plates. An average insert size of 143 kb was estimated from 217 randomly isolated clones, thus representing approximately 10-fold genome coverage. This coverage provides a very high probability that the library contains a unique sequence in genome screening. Tests on randomly selected clones demonstrated that they are very stable, with only 4 of 130 clones showing restriction digest fragment alterations after 80 generations of serial growth. FISH analysis using 70 randomly chosen PACs revealed no significant chimeric clones. About 7% of the clones analyzed contained repetitive sequences related to centromeric regions that hybridized to some but not all centromeres. DNA plate pools and superpools were made, and high-density filters each containing an array of 8 plates in duplicate were prepared. Library screening on these superpools and appropriate filters with 10 single-locus rat markers revealed an average of 8 positive clones, in agreement with the estimated high genomic coverage of this library and representation of the rat genome. This library provides a new resource for rat genome analysis, in particular the identification of genes involved in models of multifactorial disease. The library and high-density filters are currently available to the scientific community.     

Dynein inner arm heavy chain identification in cAMP-activated flagella using class-specific polyclonal antibodies

In 1993, the Medical College of Pennsylvania (MCP), mindful of the rapidly changing environments of health care delivery, created three surveys to gather information from outside the school that would help the faculty plan how the curriculum and advising system could better prepare students and residents for the demands of twenty-first-century medicine. The first survey focused on the MCP seniors graduating that year and asked about their perceptions of their medical education and their specialty and residency choices. The second survey, directed to 40 medical residency program directors in family medicine, internal medicine, pediatrics, and surgery, sought to identify the characteristics of applicants that these directors valued when selecting entrants to their programs. The third survey, of 30 employers of physicians representing four practice environments (private practice, hospitals/other health systems, academic medical centers, and health maintenance organizations), sought information on hiring and recruitment practices and the skills, competencies, and attitudes these employers valued most when hiring recently graduated physicians. The responses showed several differences and/or misperceptions among the views held by the three groups surveyed and suggest that medical educators have not adapted as rapidly as have employers to changes in the health care environment. Academic health centers must broaden their missions and make changes in their own institutional cultures, both to maintain their own viability and to train physicians who have the balance between scientific and technical competency and essential personal characteristics (such as empathy) that the next century's practice will probably demand.     

Cell membrane fluctuations are regulated by medium macroviscosity: evidence for a metabolic driving force

Extracellular fluid macroviscosity (EFM), modified by macromolecular cosolvents as occurs in body fluids, has been shown to affect cell membrane protein activities but not isolated proteins. In search for the mechanism of this phenomenon, we examined the effect of EFM on mechanical fluctuations of the cell membrane of human erythrocytes. The macroviscosity of the external medium was varied by adding to it various macromolecules [dextrans (70, 500, and 2,000 kDa), polyethylene glycol (20 kDa), and carboxymethyl-cellulose (100 kDa)], which differ in size, chemical nature, and in their capacity to increase fluid viscosity. The parameters of cell membrane fluctuations (maximal amplitude and half-width of amplitude distribution) were diminished with the elevation of solvent macroviscosity, regardless of the cosolvent used to increase EFM. Because thermally driven membrane fluctuations cannot be damped by elevation of EFM, the existence of a metabolic driving force is suggested. This is supported by the finding that in ATP-depleted red blood cells elevation of EMF did not affect cell membrane fluctuations. This study demonstrates that (i) EFM is a regulator of membrane dynamics, providing a possible mechanism by which EFM affects cell membrane activities; and (ii) cell membrane fluctuations are driven by a metabolic driving force in addition to the thermal one.     

Psychologists' attitudes and activities regarding nuclear arms.

Investigated the attitudes and activities of 297 members of the American Psychological Association (APA) concerning a nuclear freeze/disarmament, using a 20-item questionnaire. Results show that the majority of Ss agreed with the stance posited by the APA's Council of Representatives and were not supportive of psychologist/private citizen role separation. The majority of Ss participated in reading relevant literature, signing petitions, and engaging in informal discussions. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eating disorders: A call to arms.

Presents an overview of this issue of the American Psychologist. In this issue, four state-of-the-art articles on eating disorders by internationally recognized psychological scientists are presented. These articles were developed with the recognition that research in the psychological sciences constitutes an important key to realizing a pronounced decrease in the death and devastation that eating disorders leave in their wake and with the hope that there will be an increased investment in science that will lead to enlightened and effective treatments for eating disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The basal ganglia and cognitive pattern generators

This article introduces the notion of cognitive pattern generators and suggests, by analogy with the central pattern generators of the motor system, that these pattern generators operate to organize neural activity underlying aspects of action-oriented cognition. It is further proposed that the basal ganglia are involved in the control of cognitive as well as motor pattern generators. Disorders of the basal ganglia may thereby contribute to neural circuit dysfunctions that are expressed as positive and negative symptoms of schizophrenia.     

Creating a gradient material for aviation generators

The physical principles that permit the creation of gradient (nonuniform) material for rotors of powerful aviation generators are considered. The material consists of a ferromagnetic sheet of iron alloy (16.5–17.5% Cr, 7.0% Ni), obtained by cold deformation with considerable reduction, in which paramagnetic regions are formed by laser heat treatment.