Diurnal dynamics of spatial-temporal organization of lymph nodes

Experiments, performed on CBA mice demonstrate that all the parameters of lymph nodes of various localization possess a diurnal rhythmicity. Certain lympho-endocrine connections participate in realization of the regional peculiarities of the diurnal rhythms via regulation of redistribution of streams of the migrating lymphoid cells, that form the lymph node structures. There are certain differences in endogenous glucocorticoids action, depending on the level of the motor activity, that determines level of the mast cells activation, value of lymph-formation and blood stream intensity in the drained region. Concrete examples of the diurnal spatial-time organization of functional steps are described in inguinal, mesenteric and bifurcational lymph nodes.     

Single-cell models: promise and limitations.

This article describes the development of single-cell models, their uses and accomplishments, the barriers to the greater adoption, and a perspective on challenges to the biochemical engineering community where the single-cell model approach may be used advantageously. In particular, it may become an important tool in relating genomic information to cellular regulation and dynamics.     

Probing the role of multicellular organization in three-dimensional microenvironments

Successful application of living cells in regenerative medicine requires an understanding of how tissue structure relates to organ function. There is growing evidence that presentation of extracellular cues in a three-dimensional (3D) context can fundamentally alter cellular responses. Thus, microenvironment studies that previously were limited to adherent two-dimensional (2D) cultures may not be appropriate for many cell types. Here we present a method for the rapid formation of reproducible, high-resolution 3D cellular structures within a photopolymerizable hydrogel using dielectrophoretic forces. We demonstrate the parallel formation of >20,000 cell clusters of precise size and shape within a thin 2-cm(2) hydrogel and the maintenance of high cell viability and differentiated cell markers over 2 weeks. By modulating cell-cell interactions in 3D clusters, we present the first evidence that microscale tissue organization regulates bovine articular chondrocyte biosynthesis. This platform permits investigation of tissue architecture in other multicellular processes, from embryogenesis to regeneration to tumorigenesis.     

Cell organization and ultrastructure of a magnetotactic multicellular organism

Magnetotactic multicellular aggregates and many-celled magnetotactic prokaryotes have been described as spherical organisms composed of several Gram-negative bacteria capable to align themselves along magnetic fields and swim as a unit. Here we describe a similar organism collected in a large hypersaline lagoon in Brazil. Ultrathin sections and freeze fracture replicas showed that the cells are arranged side by side and face both the external environment and an internal acellular compartment in the center of the organism. This compartment contains a belt of filaments linking the cells, and numerous membrane vesicles. The shape of the cells approaches a pyramid, with the apex pointing to the internal compartment, and the basis facing the external environment. The contact region of two cells is flat and represents the pyramid faces, while the contacts of three or more cells contain cell projections and represent the edges. Freeze-fracture replicas showed a high concentration of intramembrane particles on the edges and also in the region of the outer membrane that faces the external environment. Dark field optical microscopy showed that the whole organism performs a coordinated movement with either straight or helicoidal trajectories. We conclude that the organisms described in this work are, in fact, highly organized prokaryotic multicellular organisms.     

Disruption of multicellular organization in the cellular slime molds by cyclic AMP.

Addition of cyclic AMP causes disorder in the multicellular stage of a number of species of cellular slime molds. In those which produce fruits with cellular stalks, the addition of cyclic AMP stimulates prestalk cells to differentiate into mature stalk cells. Prespore cells do not differentiate into spores under the influence of cyclic AMP, most degenerate and seem to die. I hypothesize that the normal course of differentiation from vegetative cells is one leading to spores, but that cyclic AMP can divert this course to one leading to the stalk cell. Dibutyryl cyclic AMP, cyclic GMP and cyclic AMP disrupt slugs of Polysphondylium pallidum, while species of Dictyostelium are disrupted by only cyclic AMP. The multicellular stage of P. violaceum is unaffected by high concentrations of exogenous cyclic nucleotides. Cell organization of Acytostelium ellipticum, a species with an acellular stalk, was disrupted by cyclic AMP, but no stalk cells were formed; only spores.     

Individual cell-based models of cell scatter of ARO and MLP-29 cells in response to hepatocyte growth factor

The different behaviors of colonies of two cell lines, ARO (thyroid carcinoma-derived cells) and MLP-29 (mouse liver progenitor cells), in response to hepatocyte growth factor (HGF) are described deducing suitable cellular Potts models (CPM). It is shown how increased motility and decreased adhesiveness are responsible for cell–cell dissociation and tissue invasion in the ARO cells. On the other hand, it is shown that, in addition to the biological mechanisms above, it is necessary to include directional persistence in cell motility and HGF diffusion to describe the scattering and the branching processes characteristic of MLP-29 cells.     

Regenerative medicine: Clinical relevance,implications, and limitations of the stem cell-based therapies

Many believe that success of the concept of regenerative medicine critically depends on our unlimited access to the human embryonic stem cells for scientific and therapeutic applications. Recent ground-breaking studies seem to challenge this broadly held view by demonstrating a remarkable healing power of mammalian adult (somatic) stem cells. However, mounting evidence of involvement of stemness pathways in development of therapy-resistant metastatic cancers argue for more careful considerations of potential risk and benefits associated with the stem cell-based therapies.     

The interhemispheric asymmetry of the spatial-temporal organization of cortical potentials in the rabbit]

In experiments on freely moving rabbits the existence of interhemispheric asymmetry of spatial-temporal organization of the cortical potentials in the state of calm alertness was shown. Episodes were revealed of interhemispheric discordance of spatial reconstructions of momentary reliefs of the cortical potentials topograms 1/64-1/3-1/5 s in duration, i.e. periods of the theta- or delta-rhythms. Total duration of time of interhemispheric asymmetry (according to significant divergences in dynamics of resemblance coefficients of consequent reliefs of the cortical potentials topograms) in most cases was not less than 10% and not more than 30% of time of analysis epoch and consisted of discordance episodes both of different global reconstructions of spatial correlations of the left and right hemisphere potentials and of interhemispheric local shifts in spatial organization of the cortex potentials.     

Identification of a neural alpha-catenin as a key regulator of cadherin function and multicellular organization.

The function of cadherin cell adhesion molecules is thought to be regulated by a group of cytoplasmic proteins, including alpha-catenin. We identified a subtype of alpha-catenin, termed alpha N-catenin, which is associated with N-cadherin and expressed mainly in the nervous system. cDNA transfection experiments showed that alpha N-catenin can also bind with E-cadherin. To investigate the role of alpha N-catenin, we transfected lung carcinoma PC9 cells, which express E-cadherin and beta-catenin but neither alpha- nor alpha N-catenin, with alpha N-catenin cDNA. While parental PC9 grew as isolated cells, the transfectant lines formed aggregates in which cells were tightly adhered to each other, showing epithelial arrangements, and they occasionally gave rise to cystic spheres. These results suggest that alpha N-catenin is crucial not only for cadherin function but also for organization of multicellular structures.     

Mathematical modelling of angiogenesis using continuous cell-based models

In this work, we develop a mathematical formalism based on a 3D in vitro model that is used to simulate the early stages of angiogenesis. The model treats cells as individual entities that are migrating as a result of chemotaxis and durotaxis. The phenotypes used here are endothelial cells that can be distinguished into stalk and tip (leading) cells. The model takes into account the dynamic interaction and interchange between both phenotypes. Next to the cells, the model takes into account several proteins such as vascular endothelial growth factor, delta-like ligand 4, urokinase plasminogen activator and matrix metalloproteinase, which are computed through the solution of a system of reaction–diffusion equations. The method used in the present study is classified into the hybrid approaches. The present study, implemented in three spatial dimensions, demonstrates the feasibility of the approach that is qualitatively confirmed by experimental results.     

Strengths and limitations of genetic models of ADHD

The cause and pathophysiology of attention-deficit hyperactivity disorder (ADHD) are unknown, but compelling evidence suggests an involvement of genetic factors. While dopamine is believed to play a major role in ADHD, the role for norepinephrine and serotonin systems has also been indicated. Mutant mice are valuable tools to dissect the contribution of specific neurotransmitter systems to brain dysfunction and particularly useful to decode complex multi-transmitter interaction that is critical to the pathophysiology of ADHD. Genetically altered mice provided also an opportunity to test experimentally the role of novel candidate genes for this disorder identified in genetic clinical studies. While it is clear that no rodent model would be able to recapitulate fully the complex nature of ADHD, certain endophenotypes could be reasonably well mimicked in these models. Multiple studies have reported associations between polymorphisms in dopamine transporter (DAT) gene and ADHD. Although the functional consequences of these associations are still unclear, it is believed that alterations in DAT-mediated processes might contribute to the pathogenesis of ADHD. Mice lacking the dopamine transporter have elevated dopaminergic tone and represent a genetic animal model in which certain endophenotypes of ADHD can be recapitulated. These mutants as well as other mouse models of DAT dysfunction provided an opportunity to investigate the neuronal circuitry and molecular mechanisms involved in the inhibitory action of psychostimulants on hyperactivity. Several additional knockout and transgenic mouse models have been proposed to model ADHD. Strengths and limitations of currently available genetic mouse models of ADHD are discussed.     

Cooperative response of chemically excitable membrane. II. Two-state models and their limitations

Various types of two-state models, classified by the type of direct receptorionophore coupling, were formulated based on the previously presented generalized two-state model of cooperativity (Kijima &; Kijima, 1978) and their dose-response relationships were examined. Hill coefficient at the mid-point of dose-response curve n_H^o the measure of the cooperativity of curves, is restricted for partial agonists in any two-state models because n_H^o is expressed by the product of two terms, one of which decreases when the other increases. In the independent gating unit model in which the channel opens only when the independent gating units are all in the activated state, the restriction of n_H^o is the most stringent: it never exceeds 2. In 2 ÷ 1·39 even for full agonist. It appears to be incompatible with most of the cooperative responses observed on chemically excitable membrane. In the basic model or one protomer-one channel model, n_H^o never exceeds 2·0 when 〈p〉_∞, the maximum fraction of open-channel, is less than $\text{2}\text{3}$. In the cooperative gating unit model, n_H^o is the least restricted, which is less than 2·8 when 〈p〉_∞ ≤ 0·5, but if the number of gating units, N in a receptor is practically reasonably small (N ≤ 12), n_H^o ≤ 2·0 when 〈p〉_∞ ≤ 0·58. It is discussed whether or not several representative drug-receptive membranes can be accounted for by two-state models. Response of the insect sugar receptor is out of the above limitations of two-state models and can be accounted for by three-state model. The origin of cooperative interaction can be inferred by the shapes of dose-response curves. Cooperative dose-response curves of two dimensional lattices or oligomerc systems with large number of protomers weakly interacting by long range forces bend upward more markedly at lower region than the curves of strongly interacting oligomers, when curves with the same n_H^o are compared.     

Generic physical mechanisms of morphogenesis and pattern formation as determinants in the evolution of multicellular organization

Early embryos of metazoan species are subject to the same set of physical forces and interactions as any small parcels of semi-solid material, living or nonliving. It is proposed that such “generic” properties of embryonic tissues have played a major role in the evolution of biological form and pattern by providing an array of morphological templates, during the early stages of metazoan phylogeny, upon which natural selection could act. The generic physical mechanisms considered include sedimentation, diffusion, and reaction-diffusion coupling, all of which can give rise to chemical nonuniformities (including periodic patterns) in eggs and small multicellular aggregates, and differential adhesion, which can lead to the formation of boundaries of non-mixing between adjacent cell populations. Generic mechanisms that produce chemical patterns, acting in concern with the capacity of cells to modulate their adhesivity (presumed to be a primitive, defining property of metazoa), could lead to multilayered gastrulae of various types, segmental organization, and many of the other distinguishing characteristics of extant and extinct metazoan body plans. Similar generic mechanisms, acting on small tissue primordia during and subsequent to the establishment of the major body plans, could have given rise to the forms of organs, such as the vertebrate limbs. Generic physical processes acting on a single system of cells and cell products can often produce a widely divergent set of morphological phenotypes, and these are proposed to be the raw material of the evolution of form. The establishment of any ecologically successful form by these mechanisms will be followed, under this hypothesis, by a period of genetic evolution, in which the recruitment of gene products to produce the “generically templated” morphologies by redundant pathways would be favoured by intense selection, leading to extensive genetic change with little impact on the fossil record. In this view, the stabilizing and reinforcing functions of natural selection are more important than its ability to effect incremental change in morphology. Aspects of evolution which are problematic from the standard neo-Darwinian viewpoint, or not considered within that framework, but which follow in a straightforward fashion from the view presented here, include the beginnings of an understanding of why organisms have the structure and appearance they’ do, why homoplasy (the recurrent evolution of certain forms) is so prevalent, why evolution has the tempo and mode it does (“punctuated equilibrium”), and why a “rapid” burst of morphological evolution occurred so soon after the origin of the metazoa.     

Interhemispheric asymmetry of the spatial-temporal organization of human cortical potentials during the performance of an intellectual task

In 15 healthy subjects, during accomplishment of an intellectual task spatial-temporal organization of potentials (PSTO) of the left and right cerebral hemispheres was studied by the method of quantitative evaluation of successive topograms (momentary values of potentials under leading electrodes). It was found that the time of absence of resemblance (TAR) in the cortical PSTO during intellectual activity occupied totally 10-30% of the recording time what is considerably less than in the state of calm alertness where this time varied within 4-57%. Productivity of task accomplishment apparently is connected to a greater extent with TAR than with the character of intrahemispheric reconstructions of the PSTO.