Opposing organizing forces of deposit-feeding marine communities

We contend that a range of phenomena characterizing temperate deposit-feeding communities in low-energy environments is strongly organized by two principal opposing forces: (1) spatially localized inputs of detritus or new recruits, leading to a mosaic of initial patches, with subsequent impacts on spatio-temporal variation of species with limited mobility; and (2) the impact of mobile consumers, which move to spatially localized resources and thereby exert major controls over comparatively larger spatial scales. Surface deposit feeders react differently from deep feeders, in terms of spatio-temporal population change. The two opposing community control forces, combined with responses of deposit feeder functional groups, have potentially different effects on community structure. Mobile consumers, often acting as keystone species, may move to localized patches created by the bottom-up force of food input or by localized recruitment of prey. Their mobility, combined with predicted optimal foraging behavior, would usually produce a spatially homogenizing force, leading to reduced spatial variation in community composition. By contrast, spatially localized inputs of resources, if dominant, would always lead to strong spatial heterogeneity. Dominance of complex space–time variation in detrital enrichment would lead to strong spatio-temporal complexity in macrofauna if the response of recruiting larvae and rapidly growing small invertebrate populations was immediate and keyed to localized food input. The ability of mobile consumers to locate detritus, combined with the spatial distribution and overall input rate of detritus, should determine the balance of surface and deep-feeding deposit feeders. The opposing force approach can be applied to communities generally.     

Modeling a viscoelastic gymnastics landing mat during impact

Landing mats that can undergo a large amount of area deformation are now essential for the safe completion of landings in gymnastics. The objective of this study was to develop an analytical model of a landing mat that reproduces the key characteristics of the mat-ground force during impact with minimal simulation run time. A force plate and two high-speed video cameras were used to record the mat deformation during vertical drop testing of a 24-kg impactor. Four increasingly complex point mass spring-damper models, from a single mass spring-damper system, Model 1, to a 3-layer mass spring-damper system, Model 4, were constructed using Matlab to model the mat's behavior during impact. A fifth model composed of a 3-layer mass spring-damper system was developed using visual Nastran 4D. The results showed that Models 4 and 5 were able to match the loading phase of the impact with simulation times of less than 1 second for Model 4 and 28 seconds for Model 5. Both Models 4 and 5 successfully reproduced the key force-time characteristics of the mat-ground interface, such as peak forces, time of peak forces, interpeak minima and initial rates of loading, and could be incorporated into a gymnast-mat model.     

Some anthropologic factors of performance in rhythmic gymnastics novices

The aim of the study was to determine motor and morphological factors, and to assess their impact on specific motor skill performance in rhythmic gymnastics (RG). Experimental training process aimed at learning and improving basic movement structures of rhythmic gymnastics was performed for nine months in a sample of 50 female rhythmic gymnastics novices (mean age 7.1 +/- 0.3 years). Seven dimensions in total were isolated by factorial analysis of 13 motor, 11 morphological, and 20 specific rhythmic gymnastics tests. The factors of flexibility (Beta = 0.26; p < 0.05), explosive strength (Beta = 0.25; p < 0.05) and adipose voluminosity (Beta = -0.42; p < 0.001) explains 41% of the success in performing RG basic body elements--jumps, rotations, balance and flexibility (R = 0.64), while the frequency of movement (Beta = 0.44; p < 0.001) and non-adipose voluminosity (Beta = 0.26; p < 0.05) explains 26% of RG-specific manipulations with the apparatus--club, ribbon and ball wrist manipulation (R = 0.52; p < 0.01). According to study results, the RG-training process intended for rhythmic gymnastics novices should be programmed, with preset objectives for the development of flexibility and explosive strength, speed and peripheral joint strength and adipose tissue reduction.     

Optimization of backward giant circle technique on the asymmetric bars

The release window for a given dismount from the asymmetric bars is the period of time within which release results in a successful dismount. Larger release windows are likely to be associated with more consistent performance because they allow a greater margin for error in timing the release. A computer simulation model was used to investigate optimum technique for maximizing release windows in asymmetric bars dismounts. The model comprised four rigid segments with the elastic properties of the gymnast and bar modeled using damped linear springs. Model parameters were optimized to obtain a close match between simulated and actual performances of three gymnasts in terms of rotation angle (1.5 degrees ), bar displacement (0.014 m), and release velocities (<1%). Three optimizations to maximize the release window were carried out for each gymnast involving no perturbations, 10-ms perturbations, and 20-ms perturbations in the timing of the shoulder and hip joint movements preceding release. It was found that the optimizations robust to 20-ms perturbations produced release windows similar to those of the actual performances whereas the windows for the unperturbed optimizations were up to twice as large. It is concluded that robustness considerations must be included in optimization studies in order to obtain realistic results and that elite performances are likely to be robust to timing perturbations of the order of 20 ms.     

The role of prostaglandins for the coordination of myometrial forces during labour

Systematic studies using a superfusion technique for recording myometrial contractility in vitro have been conducted in our department to explore whether prostaglandins (PG) have a differential action on the different segments of the pregnant uterus and also whether the qualitative and quantitative response undergoes a change during spontaneous labour. Myometrial specimens were excised from the fundal area and from the lower uterine segment at elective caesarean section in the 39th week of pregnancy before commencement of labour and at acute caesarean section during ongoing labour. Before labour PGF2 alpha was without or had a very weak effect on upper segment preparations but was stimulatory on lower segment specimens. PGE2 and PGI2 generally induced a biphasic dose-dependent response (stimulation followed by inhibition). During spontaneous labour PGF2 alpha and PGE2 always stimulated upper segment preparations while the contractile activity of specimens from the lower segment was inhibited by PGE2, PGF2 alpha was generally without effect. PGI2 had the same biphasic action before as during labour. With all reservations for the validity of in vitro experiments, the results favour the hypothesis that initiation of labour in the human involves a qualitative shift in the myometrial reactivity to prostaglandins. These alterations may involve suppression of expulsive forces and perhaps some tightening of the lower uterine segment during pregnancy. Following initiation of labour there is a marked increase in the excitatory action of both PGE2 and PGF2 alpha in the fundal area while the lower uterine segment reacts in a way that favours dilatation.     

The role of mechanical forces in dextral rotation during cardiac looping in the chick embryo

Cardiac looping is a vital morphogenetic process that transforms the initially straight heart tube into a curved tube normally directed toward the right side of the embryo. While recent work has brought major advances in our understanding of the genetic and molecular pathways involved in looping, the biophysical mechanisms that drive this process have remained poorly understood. This paper examines the role of biomechanical forces in cardiac rotation during the initial stages of looping, when the heart bends and rotates into a c-shaped tube (c-looping). Embryonic chick hearts were subjected to mechanical and chemical perturbations, and tissue stress and strain were studied using dissection and fluorescent labeling, respectively. The results suggest that (1) the heart contains little or no intrinsic ability to rotate, as external forces exerted by the splanchnopleure (SPL) and the omphalomesenteric veins (OVs) drive rotation; (2) unbalanced forces in the omphalomesenteric veins play a role in left-right looping directionality; and (3) in addition to ventral bending and rightward rotation, the heart tube also bends slightly toward the right. The results of this study may help investigators searching for the link between gene expression and the mechanical processes that drive looping.     

Agrin plays an organizing role in the formation of sympathetic synapses

Agrin is a nerve-derived factor that directs neuromuscular synapse formation, however its role in regulating interneuronal synaptogenesis is less clear. Here, we examine agrin's role in synapse formation between cholinergic preganglionic axons and sympathetic neurons in the superior cervical ganglion (SCG) using agrin-deficient mice. In dissociated cultures of SCG neurons, we found a significant decrease in the number of synapses with aggregates of presynaptic synaptophysin and postsynaptic neuronal acetylcholine receptor among agrin-deficient neurons as compared to wild-type neurons. Moreover, the levels of pre- and postsynaptic markers at the residual synapses in agrin-deficient SCG cultures were also reduced, and these defects were rescued by adding recombinant neural agrin to the cultures. Similarly, we observed a decreased matching of pre- and postsynaptic markers in SCG of agrin-deficient embryos, reflecting a decrease in the number of differentiated synapses in vivo. Finally, in electrophysiological experiments, we found that paired-pulse depression was more pronounced and posttetanic potentiation was significantly greater in agrin-deficient ganglia, indicating that synaptic transmission is also defective. Together, these findings indicate that neural agrin plays an organizing role in the formation and/or differentiation of interneuronal, cholinergic synapses.     

Augmin plays a critical role in organizing the spindle and phragmoplast microtubule arrays in Arabidopsis

In higher plant cells, microtubules (MTs) are nucleated and organized in a centrosome-independent manner. It is unclear whether augmin-dependent mechanisms underlie spindle MT organization in plant cells as they do in animal cells. When AUGMIN subunit3 (AUG3), which encodes a homolog of animal dim γ-tubulin 3/human augmin-like complex, subunit 3, was disrupted in Arabidopsis thaliana, gametogenesis frequently failed due to defects in cell division. Compared with the control microspores, which formed bipolar spindles at the cell periphery, the mutant cells often formed peripheral half spindles that only attached to condensed chromosomes or formed elongated spindles with unfocused interior poles. In addition, defective cells exhibited disorganized phragmoplast MT arrays, which caused aborted cytokinesis. The resulting pollen grains were either shrunken or contained two nuclei in an undivided cytoplasm. AUG3 was localized along MTs in the spindle and phragmoplast, and its signal was pronounced in anaphase spindle poles. An AUG3-green fluorescent protein fusion exhibited a dynamic distribution pattern, similar to that of the γ-tubulin complex protein2. When AUG3 was enriched from seedlings by affinity chromatography, AUG1 was detected by immunoblotting, suggesting an augmin-like complex was present in vivo. We conclude that augmin plays a critical role in MT organization during plant cell division.     

On the nature of the forces controlling selectivity in the high performance capillary electrochromatographic separation of peptides

In this minireview, the nature of the forces controlling selectivity in the high performance capillary electrochromatographic (HP-CEC) separation of peptides has been examined. For uncharged and charged peptides, a synergistic interplay occurs in HP-CEC systems between adsorptive/partitioning events and electrokinetically driven motion. Moreover, at high field strengths, both bulk electrophoretic migration and surface electrodiffusion occur. Thus, the migration behavior of peptides in different HP-CEC systems can be rationalized in terms of the combined consequences of these various processes. Moreover, in HP-CEC, the buffer electrolyte interacts with both the peptide analytes and the sorbent as bulk phenomena. These buffer-mediated processes control the solvational characteristics, ionization status and conformational behavior of the peptides as well as regulate the double-layer properties of the sorbent, and the ion flux and electro-osmotic flow characteristics of the HP-CEC system per se. These buffer electrolyte effects mediate mutual interactions between the peptide and the sorbent, irrespective of whether the interaction occurs at the surface of microparticles packed into a capillary, at the surface of a contiguous monolithic structure formed or inserted within the capillary or at the walls of the capillary as is the case with open tubular HP-CEC. Diverse molecular and submolecular forces thus coalesce to provide the basis for the different experimental modes under which HP-CEC can be carried out. As a consequence of this interplay, experimental parameters governing the separation of peptides in HP-CEC can be varied over a wide range of conditions, ensuring numerous options for enhanced selectivity, speed, and resolution of peptides. The focus of the peptide separation examples presented in this minireview has been deliberately restricted to the use of HP-CEC capillaries packed with n-alkyl-bonded silicas or mixed-mode strong ion exchange sorbents, although other types of sorbent chemistries can be employed. From these examples, several conclusions have been drawn related to the use of HP-CEC in the peptide sciences. These observations confirm that variation of a specific parameter, such as the pH or the content of the organic solvent modifier in the buffer electrolyte, simultaneously influences all other physicochemical aspects of the specific HP-CEC separation. Peptide selectivity in HP-CEC thus cannot be fine-tuned solely through the use of single parameter optimization methods. In this context, HP-CEC differs significantly from the analogous reverse phase high performance liquid chromatography (RP-HPLC) procedures with peptides. Rather, more sophisticated multiparameter optimization procedures, involving knowledge of (a) the field strength polarity, (b) its contour and flux characteristics, (c) effects of buffer electrolyte composition and pH, (e) the influence of the temperature, and (f) the impact of the sorbent characteristics, are required if the full capabilities offered by HP-CEC procedures are to be exploited. In this minireview, the HP-CEC migration behavior of several different sets of synthetic peptides has been examined, and general guidelines elaborated from these fundamental considerations to facilitate the interpretation and modulation of peptide selectivity in HP-CEC.     

The role of Otx2 in organizing the anterior patterning in mouse

Understanding the molecular mechanism controlling induction and maintenance of signals required for specifying anterior territory (forebrain and midbrain) of the central nervous system is a major task of molecular embryology. The current view indicates that in mouse, early specification of the anterior patterning is established at the beginning of gastrulation by the anterior visceral endoderm, while maintenance and refinement of the early specification is under the control of epiblast-derived tissues corresponding to the axial mesendoderm and rostral neuroectoderm. In vertebrates a remarkable amount of data has been collected on the role of genes contributing to brain morphogenesis. Among these genes,the orthodenticle group is defined bythe Drosophila orthodenticle and the vertebrate Otx1 and Otx2 genes, which contain a bicoid-like homeodomain. Mouse models and chimera experiments have provided strong evidence that Otx2 plays an important role in the specification and maintenance of the rostral neuroectoderm destined to become forebrain and midbrain. In evolutionary terms, some of these findings lead us to hypothesize a fascinating and crucial contribution of the Otx genes to the genetic program underlying the establishment of the mammalian brain.     

The role of electrostatic forces in pollination

This paper reviews research on the role of electrostatic forces in pollination, both in natural and in agricultural systems. Researchers from various fields of biological studies have reported phenomena which they related to electrostatic forces. The theory of electrostatically mediated pollen transfer between insect pollinators and the flowers they visit is described, including recent studies which confirmed that the accumulated charges on airborne honey bees are sufficient for non-contact pollen detachment by electrostatic forces (i.e., electrostatic pollination). The most important morphological features in flower adaptiveness to electrostatic pollination were determined by means of two theoretical models of a flower exposed to an approaching charged cloud of pollen; they are style length and flower opening. Supplementary pollination by using electrostatic techniques is reported, and its possible importance in modern agriculture is discussed.     

Role of the giant serotonin-containing cell of the cerebral ganglion in the edible snail in organizing its food-acquiring behavior

By adding dopamine or serotonin to a bath with snail's isolated nervous system and by intracellular activation of giant cerebral serotonergic cells it was established in neurophysiological experiments that, in spite of activating effect of serotonin on buccal motorneurones, dopamine is the transmitter triggering feeding movements of the buccal mass and feeding pattern in buccal motorneurones. This conclusion is confirmed by behavioural experiments in which an experimental group was injected by neruotoxin 5,6-dihydroxytryptamine selectively impairing serotonergic neurones. The consumatory phase of feeding (triggered by dopamine) did not change in treated animals, while the appetitive phase was significantly impaired. It was noted that the giant metacerebral cell was activated during burst activity in buccal motoneurones. The conclusion is made that giant serotonergic cerebral cells only modulate but do not trigger the feeding behaviour in the snail Helix lucorum.     

Endothelial signaling in kidney morphogenesis: a role for hemodynamic forces

The local presence of endothelial cells seems necessary for proper embryonic development of several organs. However, the signals involved are unknown. The glomerulus is generated by the coalescence of podocytes around an ingrowing capillary and is the site of blood ultrafiltration. In the absence of vessels, glomerular assembly does not occur. We describe mutations in the zebrafish that prevent glomerulogenesis. All mutants display cardiac dysfunction. Pharmacological interference with cardiac output and focal laser occlusion of the vessel similarly prevent glomerular formation. The unifying feature of all these perturbations is absence of blood flow. We find that expression of matrix metalloproteinase-2 (MMP-2), known in other systems to be regulated in a stretch-responsive manner, is in renal endothelial cells and is regulated by flow, suggesting that an MMP-2-sensitive event may be downstream of the flow-related signal. In support of this, blockade of MMP-2 activity by injection of TIMP-2 does not perturb circulation but does prevent glomerular assembly. Thus, vascular flow is required for glomerular assembly, most probably acting via a stretch-responsive signaling system in the vessel wall.     

Global analysis of mRNA localization reveals a prominent role in organizing cellular architecture and function

Although subcellular mRNA trafficking has been demonstrated as a mechanism to control protein distribution, it is generally believed that most protein localization occurs subsequent to translation. To address this point, we developed and employed a high-resolution fluorescent in situ hybridization procedure to comprehensively evaluate mRNA localization dynamics during early Drosophila embryogenesis. Surprisingly, of the 3370 genes analyzed, 71% of those expressed encode subcellularly localized mRNAs. Dozens of new and striking localization patterns were observed, implying an equivalent variety of localization mechanisms. Tight correlations between mRNA distribution and subsequent protein localization and function, indicate major roles for mRNA localization in nucleating localized cellular machineries. A searchable web resource documenting mRNA expression and localization dynamics has been established and will serve as an invaluable tool for dissecting localization mechanisms and for predicting gene functions and interactions.     

The role of shear forces in arterial branching

A new optimality principle for the branching angles of blood vessels in the cardiovascular system is proposed: the principle of minimum drag. The results are examined in the light of general observations and compared with those obtained from the principles of minimum work and minimum volume. It is shown that in some aspects the new principle is equally consistent with observations, and, in other aspects, it is perhaps more plausible than the other two principles.     

The circle of the soul: the role of spirituality in health care

This paper examines the critical attitude of behavioral professionals toward spiritual phenomena, and the current growing openness toward a scientific study of spirituality and its effects on health. Health care professionals work amidst sickness and suffering, and become immersed in the struggles of suffering persons for meaning and spiritual direction. Biofeedback and neurofeedback training can facilitate relaxation, mental stillness, and the emergence of spiritual experiences. A growing body of empirical studies documents largely positive effects of religious involvement on health. The effects of religion and spirituality on health are diverse, ranging from such tangible and easily understood phenomena as a reduction of health-risk behaviors in church-goers, to more elusive phenomena such as the distant effects of prayer on health and physiology. Psychophysiological methods may prove useful in identifying specific physiological mechanisms mediating such effects. Spirituality is also a dimension in much of complementary and alternative medicine (CAM), and the CAM arena may offer a window of opportunity for biofeedback practice.     

Effects of biomotor structures on performance of competitive gymnastics elements in elementary school female sixth-graders

In order to identify biomotor systems that determine performance of competitive gymnastics elements in elementary school female sixth-graders, factor structures of morphological characteristics and basic motor abilities were determined first, followed by relations of the morphological-motor system factors obtained with a set of criterion variables evaluating specific motor skills in competitive gymnastics in 126 female children aged 12 years +/- 3 months. Factor analysis of 17 morphological measures yielded three morphological factors: factor of mesoendomorphy and/or adipose body voluminosity; factor of longitudinal body dimensionality; and factor of transverse arm dimensionality. Factor analysis of 16 motor variables produced four motor factors: general motoricity factor (motor system); general speed factor; factor of explosive strength of throwing type (arm explosiveness); and factor of arm and leg flexibility. Three significant canonical correlations, i.e. linear combinations, explained the association between the set of seven latent variables of the morphological and basic motor system, and five variables evaluating the knowledge in competitive gymnastics. The first canonical linear combination was based on a favorable and predominant impact of the general motor factor (a system integrating whole body coordination, leg explosiveness, relative arm strength, arm movement frequency and body flexibility) on performance of gymnastics elements, cartwheel, handstand and backward pullover mount in particular, and to a lesser extent front scale and double leg pirouette for 180 degrees. The relation of the second pair of canonical factors additionally explained the role of transverse dimensionality of arm skeleton, arm flexibility and explosiveness in performing cartwheel and squat vault, whereas the relation of the third pair of canonical factors explained the unfavorable impact of adipose voluminosity on the performance of squat vault and backward pullover mount.     

On the role of the recipient cell during conjugation in Escherichia coli

To study the role of the E. coli recipient cell in conjugation recipient cell mutants deficient in conjugation (Con^-) were isolated. Mutants specific for F-type E. coli donor cells (ConF^-) and mutants specific deficient in conjugation with I-type donor cells (ConI^-) were isolated.Both ConF^- and ConI^- mutants were blocked in stable mating pair formation. Biochemical analysis of the mutants suggests that the outer membrane protein coded by the ompA gene and LPS are important for recipient activity in F-type conjugation while LPS is important for recipient activity in I-type conjugation.