A mechanical model for elongation of the acrosomal process in Thyone sperm

We present a mechanical model for the elongation of the acrosomal process in Thyone sperm based upon osmotically driven hydrostatic forces.     

Evaluation of rabbit sperm acrosomal integrity and fertilizing ability by use of vital stains.

Three staining procedures to detect sperm acrosome integrity were compared via electron microscopy. Stains were applied to epididymal, freshly ejaculated, in vivo capacitated, and sonicated sperm cells in addition to spermatozoa displaying sequentially removed plasma and outer and inner acrosomal membranes. Sequential membrane removal procedures resulted in removal of plasma membranes from 73% of all sperm cells, removal of plasma and outer acrosomal membranes from 74% of all sperm cells, and removal of plasma and outer and inner acrosomal membranes from 87% of all sperm cells as determined by electron microscopy. Live/dead staining results were not statistically different from subjective microscopic motility evaluations (P less than 0.005) for epididymal, sonicated, freshly ejaculated, and in vivo capacitated sperm samples. All three stains assessed were similarly capable of detecting the acrosome status of freshly ejaculated and of sonicated spermatozoa compared to data obtained by electron microscopy (P = 0.010). However, only the Bryan-Akruk stain afforded data that were closely correlated with data obtained via electron microscopy for all sperm types assessed; the latter included in vivo capacitated spermatozoa and sperm cells rendered free of plasma membranes. Results confirmed an earlier report by successfully effecting sequential removal of rabbit acrosomal membranes and documented use of the Bryan-Akruk acrosomal stain for evaluation of sperm cell populations for fertilizing ability. These findings should prove useful in further investigations of mechanisms involved in achievement of fertilizing ability by rabbit spermatozoa.     

Modelling the swelling assay for aquaporin expression

The standard method of assaying the water transporting capability of a putative aquaporin-like entity is to express that entity in a cell of normally low water permeability and to measure the enhancement of swelling when the cell is subjected to hypo-osmotic shock. Because of the heterogeneous nature of cytoplasm, the interplay of advection and diffusion, and the coupling of internal and external media via a semipermeable elastic membrane, even simplified mathematical models can be difficult to resolve. This class of diffusion problem seems to have been but little studied. In this paper, the cell and its surround are at first modelled as perfectly-mixed phases separated by an ideal semipermeable membrane with vanishingly small elastic modulus; and the time course of swelling is evaluated analytically. This time course was found to be non-exponential, but such unexpected behavior should not seriously affect the traditional interpretation of experimental results because its short time limit is linear as in the traditional model; and normally only short time data are available. Next, the simplifications of diffusive equilibrium and of vanishing elastic modulus are examined. It is shown that diffusive equilibrium will be true only when diffusive movement of osmolyte is rather faster than the swelling and that this will probably not be the case for many assays. On the other hand, it should often be possible to neglect the elastic modulus. Finally, a more comprehensive model is formulated for a spherical cell in a hypotonic medium and the swelling behavior described in terms as a moving boundary problem (This type of moving boundary problem is often called a Stefan problem [ http://en.wikipedia.org/wiki/Stefan_problem ]) in which two phases containing diffusive osmolyte are separated by a weakly-elastic ideally-semipermeable membrane, the water flux across which is linear in the osmolality difference across it. This type of behavior was evaluated numerically by finite-difference time-domain techniques and found to be qualitatively similar to that of the perfect-mixing simplification.     

Vegetation boundary detection: A comparison of two approaches applied to field data

We examined and compared two approaches to vegetation boundarydetermination by applying them to field data collected from Betsch Fen, analkaline wetland in Ohio, USA. Two boundary detection methods were used to testhypothesized boundary locations determined through field observations: gradientanalysis by detrended correspondence analysis (DCA) and the moving split-window(MSW) technique. These two methods represent approaches suggested by vegetationanalysis and landscape ecological literature, respectively. DCA was moresuccessful in detecting vegetation changes at the community level, but it wasoften difficult to extrapolate this information to a landscape context. Incontrast, MSW detected changes at a landscape level which overestimated minorshifts in species composition at the community level. Although results from MSWwere more easily interpretable, neither method completely confirmedhypothesizedboundary locations derived from field reconnaissance and aerial photo analysis.While DCA and MSW can be used in conjunction to provide maximum information onboundary location and ecological significance, this would be unrealistic inpractical applications because of the time and effort required to do bothsimultaneously. We suggest an approach using primarily MSW principles, whichtake into consideration community-level information and optimum sampling plotplacement and spacing.     

A direct-transfer polymerization model explains how the multiple profilin-binding sites in the actoclampin motor promote rapid actin-based motility

The high actin-based motility rates observed in nonmuscle cells require the per-second addition of 400-500 monomers to the barbed ends of growing actin filaments. The chief polymerization-competent species is profilin.actin.ATP (present at 5-40 microM intracellular concentrations), whereas G-actin.ATP is much less abundant ( approximately 0.1-1 microM). While earlier studies unambiguously demonstrated that profilin.actin is highly concentrated within the polymerization zone, profilin-actin localization on the motile surface cannot increase the local solution-phase concentration of polymerizable actin. To explain these high rates of actin polymerization, we present and analyze a novel polymerization model in which monomers are directly transferred to growing filament ends in the actoclampin motor. This direct-transfer polymerization mechanism endows the polymerization zone with properties unavailable to bulk-phase actin monomers, and our model also indicates why profilin is the ideal mobile carrier for actin monomers.     

A cross-diffusion model of forest boundary dynamics

A simple mathematical model of mono-species forest with two age classes which takes into account seed production and dispersal is presented in the paper. This reaction — diffusion type model is then reduced by means of an asymptotic procedure to a lower dimensional reaction — cross-diffusion model. The existence of standing and travelling wave front solutions corresponding to the forest boundary is shown for the later model. On the basis of the analysis, possible changes in forest boundary dynamics caused by antropogenic impacts are discussed.     

Novel tracking function of moving target using chaotic dynamics in a recurrent neural network model

Chaotic dynamics introduced in a recurrent neural network model is applied to controlling an object to track a moving target in two-dimensional space, which is set as an ill-posed problem. The motion increments of the object are determined by a group of motion functions calculated in real time with firing states of the neurons in the network. Several cyclic memory attractors that correspond to several simple motions of the object in two-dimensional space are embedded. Chaotic dynamics introduced in the network causes corresponding complex motions of the object in two-dimensional space. Adaptively real-time switching of control parameter results in constrained chaos (chaotic itinerancy) in the state space of the network and enables the object to track a moving target along a certain trajectory successfully. The performance of tracking is evaluated by calculating the success rate over 100 trials with respect to nine kinds of trajectories along which the target moves respectively. Computer experiments show that chaotic dynamics is useful to track a moving target. To understand the relations between these cases and chaotic dynamics, dynamical structure of chaotic dynamics is investigated from dynamical viewpoint.     

二维细胞运动模型的数值模拟

研究了一个二维细胞运动模型,该模型是个动边界问题．我们运用运动网格的有限元算法对此模型进行了数值模拟,数值结果表明,细胞最终收敛到固定形状,并且以固定速度向前运动．     

On the use of split moving window analysis for boundary detection in ordered dataseries from benthic communities

The capacity of Split Moving Window (SMW) boundary analysis was tested to detect the depth of the transition of a littoral to a profundal invertebrate community in two datasets that were ordered along a depth gradient. The littoral community was dominated byPolypedilum nubeculosum agg.,Potamopyrgus jenkinsi andGlyptotendipes cf.pallens. The species richness of the profundal community was much lower. Its fauna was dominated byChironomus cf.plumosus andChaoborus flavicans. The transition could be detected with small window sizes. The discontinuities are located at the same depth as the oxygen stratification. We conclude that SMW can be used to study artificial transects. Noisy datasets should be transformed to reduce the variation. The scale dependence of SMW is an advantage. Information about the nature of a discontinuity (transition, trend or local discontinuity) can be obtained by increasing the window size. The location of discontinuities that are detected at the edge of a series, with large windows, should be interpreted carefully due to the existence of a blind zone.     

Human sperm acrosomal status,acrosomal responsiveness,and acrosin are predictive of the outcomes of in vitro fertilization: A prospective cohort study

The sperm acrosome reaction (AR) is a physiological secretory course of membrane fusion and hydrolytic enzymes, as well as matrix protein release, enabling spermatozoa to penetrate the egg surroundings. An instable acrosomal status before a specific stimulus, insufficient acrosomal responsiveness, or inadequate enzymatic activity of acrosomal content can be detrimental to male fertility. This prospective cohort study was designed to determine whether three human sperm acrosome evaluation parameters—including spontaneous AR rate, AR after calcium ionophore A23187 challenge (ARIC) rate, and modified Kennedy acrosin activity—can predict fertilization outcomes in vitro and are correlated with male characteristics. A total of 485 eligible couples undergoing in vitro fertilization (IVF) therapy were included in two phases of this study. In a ‘construction phase’, three acrosome evaluation parameters were determined simultaneously in 132 cases, whereas in a ‘validation phase’, the spontaneous AR rate was determined in 353 cases. The results of the ‘construction phase’ revealed that the spontaneous AR rate was the only significant predictor of fertilization outcome (unadjusted odds ratio [OR]?=?0.68, 95% confidence interval [CI]: 0.53–0.88, P?=? 0.003; adjusted OR = 0.64, 95% CI: 0.43–0.95, P?=? 0.03), and the cut-off value for total fertilization failure (TFF) prediction, determined by ROC curve analysis, was 9.91%; higher acrosin activity was shown to predict a higher fertilization rate only when patients were divided into groups (≥25 μIU/10⁶ spermatozoa, 14–25 μIU/10⁶ spermatozoa, <14 μIU/10⁶ spermatozoa). The spontaneous AR rate was negatively correlated with sperm motility, forward progression motility, and normal morphology; modified Kennedy acrosin activity was positively correlated with normal morphology; and the ARIC rate was not correlated with any of the male characteristics. A similar result was obtained for the spontaneous AR rate in the ‘validation phase’, and the cut-off value in predicting TFF was calibrated for 9.52%. Clinically, patients can voluntarily choose spontaneous AR rate alone or in combination with modified Kennedy acrosin activity to predict TFF, and early rescue intracytoplasmic sperm injection (ICSI), half ICSI, or full ICSI should be considered in advance for men with spontaneous AR rates ≥9.52% or spontaneous AR rates ≥9.52% and AE activities <25 μIU/10⁶ spermatozoa.     

A mathematical analysis of physiological and morphological aspects of wound closure

A computational algorithm to study the evolution of complex wound morphologies is developed based on a model of wound closure by cell mitosis and migration due to Adam [Math Comput Model 30(5–6):23–32, 1999]. A detailed analysis of the model provides estimated values for the incubation and healing times. Furthermore, a set of inequalities are defined which demarcate conditions of complete, partial and non-healing. Numerical results show a significant delay in the healing progress whenever diffusion of the epidermic growth factor responsible for cell mitosis is slower than cell migration. Results for general wound morphologies show that healing is always initiated at regions with high curvatures and that the evolution of the wound is very sensitive to physiological parameters.      

Propagation of Turing patterns in a plankton model

The paper is devoted to a reaction–diffusion system of equations describing phytoplankton and zooplankton distributions. Linear stability analysis of the model is carried out. Turing and Hopf stability boundaries are found. Emergence of two-dimensional spatial structures is illustrated by numerical simulations. Travelling waves between various stationary solutions are investigated. Transitions between homogeneous in space stationary solutions and Turing structures are studied.     

Proteomic characterization of Jurkat T leukemic cells after dopamine stimulation: A model of circulating dopamine-sensitive cells

T-cells are circulating dopamine-sensitive cells and may mirror, at the peripheral level, biochemical modifications occurring in dopaminergic neurons. The human CD4+ T leukemic Jurkat cell line has been thoroughly used and characterized as a suitable cell model to investigate T-cell signaling and apoptosis. Here, we describe their characterization as a model of circulating dopamine-sensitive cells and their response to a dopamine challenge by analyzing changes in the cell proteome. Jurkat cells express both D1- and D2-like dopamine receptors and both membrane and vesicular transporters, while they lack D4 receptor and tyrosine hydroxylase expression. A saturating, non-toxic, non-oxidant 50 μM dopamine challenge induces the upregulation of an interacting chaperone network known to protect specifically dopaminergic neurons, thus validating T-cells as a biomarker discovery source in Parkinson’s disease. Remodeling of the distribution pattern of β-actin and 14-3-3 isoforms is consistently observed upon dopamine treatment. As a whole, dopamine-specific alterations here observed might represent a biosensor for dopamine response at the peripheral level.     

The extracellular protein coat of the inner acrosomal membrane is involved in zona pellucida binding and penetration during fertilization: characterization of its most prominent polypeptide (IAM38)

A consequence of the acrosome reaction is to expose the inner acrosomal membrane (IAM), which is a requirement for the sperm's ability to secondarily bind to and then penetrate the zona pellucida (ZP) of the mammalian oocyte. However, the proteins on the IAM responsible for binding and presumably penetrating the zona have not been identified. This issue can be resolved if direct information is made available on the composition of the IAM. For this purpose, we devised a methodology in order to obtain a sperm head fraction consisting solely of the IAM bound to the detergent-resistant perinuclear theca. On the exposed IAM surface of this fraction, we defined an electron dense protein layer that we termed the IAM extracellular coat (IAMC), which was visible on sonicated and acrosome-reacted sperm of several mammalian species. High salt extraction removed the IAMC coincident with the removal of a prominent 38 kDa polypeptide, which we termed IAM38. Antibodies raised against this polypeptide confirmed its presence in the IAMC of intact, sonicated and acrosome-reacted sperm. By immunoscreening of a bovine testicular cDNA library and sequencing the resulting clones, we identified IAM38 as the equivalent of porcine Sp38 [Mori, E., Kashiwabara, S., Baba, T., Inagaki, Y., Mori, T., 1995. Amino acid sequences of porcine Sp38 and proacrosin required for binding to the zona pellucida. Dev. Biol., 168, 575-583], an intra-acrosomal protein with ZP-binding ability, whose precise localization in sperm was unknown. The blockage of IVF at the level of the zona with anti-IAM38 antibodies and the retention of IAM38 after sperm passage through the zona support its involvement in secondary sperm-zona binding. This study provides a novel approach to obtain direct information on the peripheral and integral protein composition of the IAM for identifying other candidates for sperm-zona interactions.     

A computational model of cell migration coupling the growth of focal adhesions with oscillatory cell protrusions

Cell migration is a highly integrated process where actin turnover, actomyosin contractility, and adhesion dynamics are all closely linked. In this paper, we propose a computational model investigating the coupling of these fundamental processes within the context of spontaneous (i.e. unstimulated) cell migration. In the unstimulated cell, membrane oscillations originating from the interaction between passive hydrostatic pressure and contractility are sufficient to lead to the formation of adhesion spots. Cell contractility then leads to the maturation of these adhesion spots into focal adhesions. Due to active actin polymerization, which reinforces protrusion at the leading edge, the traction force required for cell translocation can be generated. Computational simulations first show that the model hypotheses allow one to reproduce the main features of fibroblast cell migration and established results on the biphasic aspect of the cell speed as a function of adhesion strength. The model also demonstrates that certain temporal parameters, such as the adhesion proteins recycling time and adhesion lifetimes, influence cell motion patterns, particularly cell speed and persistence of the direction of migration. This study provides some elements, which allow a better understanding of spontaneous cell migration and enables a first glance at how an individual cell would potentially react once exposed to a stimulus.     

A major mutation of KIF21A associated with congenital fibrosis of the extraocular muscles type 1 (CFEOM1) enhances translocation of Kank1 to the membrane

Congenital fibrosis of the extraocular muscles type 1 (CFEOM1) is associated with heterozygous mutations in the KIF21A gene, including a major (R954W) and a minor (M947T) mutation. Kank1, which regulates actin polymerization, cell migration and neurite outgrowth, interacted with the third and fourth coiled-coil domains of KIF21A protein at its ankyrin-repeat domain. While both KIF21A^R954W and KIF21A^M947T enhanced the formation of a heterodimer with the wild type, KIF21A^WT, these mutants also enhanced the interaction with Kank1. Knockdown of KIF21A resulted in Kank1 predominantly occurring in the cytosolic fraction, while KIF21A^WT slightly enhanced the translocation of Kank1 to the membrane fraction. Moreover, KIF21A^R954W significantly enhanced the translocation of Kank1 to the membrane fraction. These results suggest that KIF21A regulates the distribution of Kank1 and that KIF21A mutations associated with CFEOM1 enhanced the accumulation of Kank1 in the membrane fraction. This might cause an abrogation of neuronal development in cases of CFEOM1 through over-regulation of actin polymerization by Kank1.     

A functional-structural model of elongation of the grass leaf and its relationships with the phyllochron

The emergence of a regular phyllochron from the dynamic processes of leaf initiation, leaf elongation and whorl construction suggests causal relationships between leaf elongation and leaf emergence. This paper presents a hypothesis as to how the ontogeny of the growth zone of leaves is triggered by emergence events, and implements it in a dynamic model of leaf elongation. Two different experiments, presenting two contrasted cases of relationships between leaf emergence and kinetics of leaf elongation, were analysed and interpreted with the model in terms of the functioning of the growth zone. Analysis of elongation kinetics revealed that the hypothesis allows for several contrasted elongation patterns that were observed, and for a regular phyllochron emerging from the variable dynamic of elongation. The model was able to simulate these patterns, and helped to identify the mechanisms underlying the key points of the analysis. The hypothesis is not demonstrated, but its coherence and robustness are established, which should inform a renewal of the modelling of leaf elongation in architectural models.     

Actin bundling and polymerisation properties of eukaryotic elongation factor 1 alpha (eEF1A), histone H2A-H2B and lysozyme in vitro

Elongation factor 1 alpha (eEF1A) is a positively charged protein which has been shown to interact with the actin cytoskeleton. However, to date, a specific actin binding site within the eEF1A sequence has not been identified and the mechanism by which eEF1A interacts with actin remains unresolved. Many protein–protein interactions occur as a consequence of their physicochemical properties and actin bundle formation has been shown to result from non-specific electrostatic interaction with basic proteins. This study investigated interactions between actin, eEF1A and two other positively charged proteins which are not regarded as classic actin binding proteins (namely lysozyme and H2A–H2B) in order to compare their actin organising effects in vitro. For the first time using atomic force microscopy (AFM) we have been able to image the interaction of eEF1A with actin and the subsequent bundling of actin in vitro. Interestingly, we found that eEF1A dramatically increases the rate of polymerisation (45-fold above control levels). We also show for the first time that H2A–H2B has remarkably similar effects upon actin bundling (relative bundle size/number) and polymerisation (35-fold increase above control levels) as eEF1a. The presence of lysozyme resulted in bundles which were distinct from those formed due to eEF1A and H2A–H2B. Lysozyme also increased the rate of actin polymerisation above the control level (by 10-fold). Given the striking similarities between the actin bundling and polymerisation properties of eEF1A and H2A–H2B, our results hint that dimerisation and electrostatic binding may provide clues to the mechanism through which eEF1A-actin bundling occurs.