Redundant mechanisms for stable cell locomotion revealed by minimal models

Crawling of eukaryotic cells on flat surfaces is underlain by the protrusion of the actin network, the contractile activity of myosin II motors, and graded adhesion to the substrate regulated by complex biochemical networks. Some crawling cells, such as fish keratocytes, maintain a roughly constant shape and velocity. Here we use moving-boundary simulations to explore four different minimal mechanisms for cell locomotion: 1), a biophysical model for myosin contraction-driven motility; 2), a G-actin transport-limited motility model; 3), a simple model for Rac/Rho-regulated motility; and 4), a model that assumes that microtubule-based transport of vesicles to the leading edge limits the rate of protrusion. We show that all of these models, alone or in combination, are sufficient to produce half-moon steady shapes and movements that are characteristic of keratocytes, suggesting that these mechanisms may serve redundant and complementary roles in driving cell motility. Moving-boundary simulations demonstrate local and global stability of the motile cell shapes and make testable predictions regarding the dependence of shape and speed on mechanical and biochemical parameters. The models shed light on the roles of membrane-mediated area conservation and the coupling of mechanical and biochemical mechanisms in stabilizing motile cells.     

Experiments and models of sensorimotor interactions during locomotion

During locomotion sensory information from cutaneous and muscle receptors is continuously integrated with the locomotor central pattern generator (CPG) to generate an appropriate motor output to meet the demands of the environment. Sensory signals from peripheral receptors can strongly impact the timing and amplitude of locomotor activity. This sensory information is gated centrally depending on the state of the system (i.e., rest vs. locomotion) but is also modulated according to the phase of a given task. Consequently, if one is to devise biologically relevant walking models it is imperative that these sensorimotor interactions at the spinal level be incorporated into the control system.     

Cell-substrate interactions during amoeboid locomotion of neutrophil leukocytes

Cell-substrate interactions between human blood neutrophils moving on a glass substrate in serum-free medium have been investigated using reflexion interference microscopy, high voltage and scanning electron microscopy (SEM). The contact pattern with the substrate differed considerably from that found in fibroblasts and the amoeba Naegleria. Discrete focal contacts could not be detected but large broad areas of very close contact (accounting for about 30% of the total contact area) could be found particularly associated with the uroid. Considerable loss of membrane material occurred as a result of breakdown of the uroid during locomotion.     

A simple method for detecting heparinase-producing bacteria

A simple method for detecting heparinase-producing bacteria is described. The method is based on the metachromatic reaction between heparin and toluidine blue. Though developed primarily for Bacteroides spp., the method should find application in the detection of other aerobic and anaerobic heparinase-producing bacteria, without the need for large amounts of media and expensive spectrophotometric equipment.     

Cardiovascular responses during spontaneous overground locomotion in freely moving decerebrate cats

Sadamoto, Tomoko, and Kanji Matsukawa. Cardiovascularresponses during spontaneous overground locomotion in freely movingdecerebrate cats. J. Appl. Physiol.83(5): 1454-1460, 1997.To examine whether the cerebrum isessential for producing the rapid cardiovascular adjustment at thebeginning of overground locomotion, we examined heart rate (HR), meanarterial blood pressure (MAP), and integrated electromyogram (iEMG) ofthe forelimb triceps brachialis muscle in freely moving decerebratecats during locomotion. Two to four days after decerebration surgeryperformed at the level of the precollicular-premammillary body, theanimals spontaneously produced coordinated overground locomotion,supporting body weight. HR began to increase immediately before theonset of iEMG, and MAP began to rise almost simultaneously with theiEMG onset. Their increases in HR and MAP (24 ± 3 beats/min and 22 ± 4 mmHg) were sustained during locomotion. Sinoaortic denervation(SAD) did not affect the abrupt changes in HR and MAP at the beginningof locomotion (0-4 s from the onset of iEMG), whereas SAD had acontrasting effect during the subsequent period, a decrease in the HRresponse (9 ± 1 beats/min) and an increase in the MAP response (30 ± 3 mmHg). These results suggest that the cerebrum and the rostral part of the diencephalon are not essential for producing the rapid cardiovascular adjustment at the beginning of spontaneous overground locomotion. The arterial baroreflex does not contribute to this rapidadjustment but plays an important role in regulating the cardiovascularresponses during the later period of spontaneous locomotion.

     

Bird terrestrial locomotion as revealed by 3D kinematics

Most birds use at least two modes of locomotion: flying and walking (terrestrial locomotion). Whereas the wings and tail are used for flying, the legs are mainly used for walking. The role of other body segments remains, however, poorly understood. In this study, we examine the kinematics of the head, the trunk, and the legs during terrestrial locomotion in the quail (Coturnix coturnix). Despite the trunk representing about 70% of the total body mass, its function in locomotion has received little scientific interest to date. This prompted us to focus on its role in terrestrial locomotion. We used high-speed video fluoroscopic recordings of quails walking at voluntary speeds on a trackway. Dorso-ventral and lateral views of the motion of the skeletal elements were recorded successively and reconstructed in three dimensions using a novel method based on the temporal synchronisation of both views. An analysis of the trajectories of the body parts and their coordination showed that the trunk plays an important role during walking. Moreover, two sub-systems participate in the gait kinematics: (i) the integrated 3D motion of the trunk and thighs allows for the adjustment of the path of the centre of mass; (ii) the motion of distal limbs transforms the alternating forward motion of the feet into a continuous forward motion at the knee and thus assures propulsion. Finally, head bobbing appears qualitatively synchronised to the movements of the trunk. An important role for the thigh muscles in generating the 3D motion of the trunk is suggested by an analysis of the pelvic anatomy.     

A simple enzyme immunoassay for detecting brucellosis antibodies

Abstract A simple enzyme immunoassay was developed and evaluated for serological diagnosis of brucellosis in 25 patients with various forms of brucellosis and 292 control patients with other conditions and disorders. All brucellosis patients gave a positive test with the initial sample. In 3 acute, febrile brucellosis patients with follow-up sera taken during therapy a sharp drop in specific antibody was noted. There was a less pronounced antibody reduction in 1 chronic and 2 relapse patients and an antibody increase in 1 chronic and 1 relapse case. All control samples gave negative results. In addition, the assay was evaluated as a screening test with 315 sera from 'healthy' individuals living in a brucellosis focus and representing 15% of that population. 11.5% (34/293) of subjects with no reported history of brucellosis and 45% (10/22) of cases treated in the past gave a positive test result. The agreement in those samples between the assay and the serum agglutination test was 95.5%.     

A novel evolution-based method for detecting gene-gene interactions

Background

The rapid advance in large-scale SNP-chip technologies offers us great opportunities in elucidating the genetic basis of complex diseases. Methods for large-scale interactions analysis have been under development from several sources. Due to several difficult issues (e.g., sparseness of data in high dimensions and low replication or validation rate), development of fast, powerful and robust methods for detecting various forms of gene-gene interactions continues to be a challenging task.

Methodology/Principal Findings

In this article, we have developed an evolution-based method to search for genome-wide epistasis in a case-control design. From an evolutionary perspective, we view that human diseases originate from ancient mutations and consider that the underlying genetic variants play a role in differentiating human population into the healthy and the diseased. Based on this concept, traditional evolutionary measure, fixation index (Fst) for two unlinked loci, which measures the genetic distance between populations, should be able to reveal the responsible genetic interplays for disease traits. To validate our proposal, we first investigated the theoretical distribution of Fst by using extensive simulations. Then, we explored its power for detecting gene-gene interactions via SNP markers, and compared it with the conventional Pearson Chi-square test, mutual information based test and linkage disequilibrium based test under several disease models. The proposed evolution-based method outperformed these compared methods in dominant and additive models, no matter what the disease allele frequencies were. However, its performance was relatively poor in a recessive model. Finally, we applied the proposed evolution-based method to analysis of a published dataset. Our results showed that the P value of the Fst -based statistic is smaller than those obtained by the LD-based statistic or Poisson regression models.

Conclusions/Significance

With rapidly growing large-scale genetic association studies, the proposed evolution-based method can be a promising tool in the identification of epistatic effects.     

A simple strategy for jumping straight up

Jumping from a stationary standing position into the air is a transition from a constrained motion in contact with the ground to an unconstrained system not in contact with the ground. A simple case of the jump, as it applies to humans, robots and humanoids, is studied in this paper. The dynamics of the constrained rigid body are expanded to define a larger system that accommodates the jump. The formulation is applied to a four-link, three-dimensional system in order to articulate the ballistic motion involved. The activity of the muscular system and the role of the major sagittal muscle groups are demonstrated. The control strategy, involving state feedback and central feed forward signals, is formulated and computer simulations are presented to assess the feasibility of the formulations, the strategy and the jump.     

A moving topic: control and dynamics of animal locomotion

Animal locomotion arises from complex interactions among sensory systems, processing of sensory information into patterns of motor output, the musculo-skeletal dynamics that follow motor stimulation, and the interaction of appendages and body parts with the environment. These processes conspire to produce motions and forces that permit stunning manoeuvres with important ecological and evolutionary consequences. Thus, the habitats that animals may exploit, their ability to escape predators or attack prey, their capacity to manoeuvre and turn, or the use of their available energy all depend upon the processes that determine locomotion. Here, we summarize a series of 10 papers focused on this integrative research topic.     

A simple method for estimation of phospholipids in biological objects

A simple method to estimate phospholipids is elaborated. This method is based on determination of optical density of phospholipid-molybdate complexes in chloroform. The method is used for the quantitative determination of phospholipids in biomembranes, liposomes and blood serum without their preliminary extraction, as well as in chloroform, methanol and chloroform-methanol solutions. It is also modified for the phospholipids determination in chromatographic fractions on silufol plates.     

A strategy for detecting chromosome-specific rearrangements in rye.

To obtain translocations involving specific chromosomes in rye, a line in which chromosome 1R has large C-bands on its two telomeres but which lacks C-bands (or has very small ones) on the telomeres of the remaining chromosomes was used. About 6% of the plants produced using pollen from irradiated (1.2 krad (1 rad = 10 mGy)) spikes of this line possessed structural changes involving the labeled chromosome. These aberrations included translocations, ring chromosomes, isochromosomes, and telocentrics. It is concluded (i) that all nonlabeled chromosomes have the same probability of participating in reciprocal translocations with the labeled chromosome, 1R, and (ii) that most induced reciprocal translocations involved exchanges of chromosome segments of approximately equal length. The use of lines having the appropriate combination of telomeric C-bands improves the efficiency of obtaining reciprocal translocations involving specific chromosomes that could be used in the construction of detailed physical maps.     

A label-free optical technique for detecting small molecule interactions

A novel approach for the label-free detection of molecular interactions is presented in which a colorimetric resonant grating is used as a surface binding platform. The grating, when illuminated with white light, is designed to reflect only a single wavelength. When molecules are attached to the surface, the reflected wavelength (color) is shifted due to the change of the optical path of light that is coupled into the grating. By linking receptor molecules to the grating surface, complementary binding molecules can be detected without the use of any kind of fluorescent probe or radioactive label. The detection technique is capable of detecting the addition and removal of small molecules as they interact with receptor molecules on the sensor surface or enzymes in the solution surrounding the sensor. Two assays are presented to exemplify the detection of small molecule interactions with the biosensor. First, an avidin receptor layer is used to detect 244 Da biotin binding. Second, a protease assay is performed in which a 136 Da p-nitroanilide (pNA) moeity is cleaved from an immobilized substrate. Because the sensor structure can be embedded in the plastic surfaces of microtiter plates or the glass surfaces of microarray slides, it is expected that this technology will be most useful in applications where large numbers of biomolecular interactions are measured in parallel, particularly when molecular labels will alter or inhibit the functionality of the molecules under study. Screening of pharmaceutical compound libraries with protein targets, and microarray screening of protein-protein interactions for proteomics are examples of applications that require the sensitivity and throughput afforded by this approach.