Flow and Diffusion in Channel-Guided Cell Migration

Collective migration of mechanically coupled cell layers is a notable feature of wound healing, embryonic development, and cancer progression. In confluent epithelial sheets, the dynamics have been found to be highly heterogeneous, exhibiting spontaneous formation of swirls, long-range correlations, and glass-like dynamic arrest as a function of cell density. In contrast, the flow-like properties of one-sided cell-sheet expansion in confining geometries are not well understood. Here, we studied the short- and long-term flow of Madin-Darby canine kidney (MDCK) cells as they moved through microchannels. Using single-cell tracking and particle image velocimetry (PIV), we found that a defined averaged stationary cell current emerged that exhibited a velocity gradient in the direction of migration and a plug-flow-like profile across the advancing sheet. The observed flow velocity can be decomposed into a constant term of directed cell migration and a diffusion-like contribution that increases with density gradient. The diffusive component is consistent with the cell-density profile and front propagation speed predicted by the Fisher-Kolmogorov equation. To connect diffusion-mediated transport to underlying cellular motility, we studied single-cell trajectories and occurrence of vorticity. We discovered that the directed large-scale cell flow altered fluctuations in cellular motion at short length scales: vorticity maps showed a reduced frequency of swirl formation in channel flow compared with resting sheets of equal cell density. Furthermore, under flow, single-cell trajectories showed persistent long-range, random-walk behavior superimposed on drift, whereas cells in resting tissue did not show significant displacements with respect to neighboring cells. Our work thus suggests that active cell migration manifests itself in an underlying, spatially uniform drift as well as in randomized bursts of short-range correlated motion that lead to a diffusion-mediated transport.     

A complex species complex: The controversial role of ecology and biogeography in the evolutionary history of Syllis gracilis Grube, 1840 (Annelida,Syllidae)

The cryptic diversity in the polychaete Syllis gracilis Grube, 1840, in the Mediterranean Sea was examined with an integrative morpho-molecular approach. Individuals of S. gracilis were collected at eleven Mediterranean localities to provide an insight into the role of brackish environments in inducing cryptic speciation. The examination of morphological features combined with a molecular genetic analysis based on a partial sequence of the 16S rRNA gene highlighted discrepancies between morphological and molecular diversity. Morphological data allowed to identify a morphotype with short appendages occurring in coralline algae communities and another one with long appendages observed in brackish-water environments and Sabellaria reefs. Multivariate analyses showed that sampling localities were the greatest source of morphological divergence, suggesting that phenotypic plasticity may play a role in local adaptations of S. gracilis populations. Molecular data showed the occurrence of four divergent lineages not corresponding to morphological clusters. Different species delimitation tests gave conflicting results, retrieving, however, at least four separated entities. Some lineages occurred in sympatry and were equally distributed in marine and brackish-water environments, excluding a biogeographic or ecological explanation of the observed pattern and suggesting instead ancient separation between lineages and secondary contact. The co-occurrence of different lineages hindered the identification of the lineage corresponding to S. gracilis sensu stricto. The discrepancy between morphological and molecular diversity suggests that different environmental and biogeographic features may interact in a complex and unpredictable way in shaping diversity patterns. An integrative approach is needed to provide a satisfactory insight on evolutionary processes in marine invertebrates.     

TF — A novel cell-permeable and selective inhibitor of human protein kinase CK2 induces apoptosis in the prostate cancer cell line LNCaP

BackgroundAbnormally high activity of protein kinase CK2 is linked to various diseases including cancer. Therefore, the inhibition of CK2 is a promising therapeutic strategy to fight this disease.MethodsWe screened a library of synthetic molecules concerning their capacity to inhibit CK2. The activity of CK2 and their IC₅₀ and K_i values were determined by a capillary electrophoresis assay. The effects of the inhibitor in a cell culture model were analyzed by cell counting, a viability assay, cytofluorimetry and Western blot.ResultsThe best CK2 inhibitor found in this screen was 6,7-dichloro-1,4-dihydro-8-hydroxy-4-[(4-methylphenylamino)methylen]dibenzo [b,d]furan-3(2H)-one, which we refer to as “TF”. TF showed tight binding to CK2 with low IC₅₀ (29 nM) and K_i (15 nM) values. TF inhibited only seven out of 61 human kinases tested (> 70% inhibition). Incubation of LNCaP cells with 50 μM TF for 48 h decreased the intracellular CK2 activity by 50%, confirming that the inhibitor is membrane permeable. The decrease in activity was correlated with a severe reduction in cell viability. The reduction in cell viability is at least partly due to the induction of apoptosis.General significanceIn many cancers the protein kinase CK2 is significantly up-regulated and supports the neoplastic phenotype. New therapeutic strategies should be based on diverse reliable inhibitors to reverse the abnormal high levels to normal settings.     

Biological rhythms in birds — development, insights and perspectives

The aim of this review is to show that probably the internal clock of precocial birds is imprinted in the prenatal period by exogenous factors (zeitgeber). The activity of organ functions occurs early during embryonic development, before this function is ultimately necessary to ensure the survival of the embryo. Prenatal activation of some functional systems may have a training effect on the postnatal efficiency.The development of physiological control systems is influenced by endogenous and exogenous factors during the late prenatal and early postnatal period: epigenetic adaptation processes play an important role in the development of animals; they have acquired characteristics which are innated but not genetically fixed. As a rule, the actual value during the determination period has a very strong influence on the set-point of the system. This will be explained using the example of thermoregulation.It is shown in detail that it seems to be possible to imprint the prenatal development of circadian rhythms by periodic changes of the light-dark cycle but not by rhythmic influence of acoustic signals.Altogether, there are more questions open than solved concerning the perinatal genesis of circadian rhythms in birds. Topics are given for the future research.     

The genetics of chemotaxis in Drosophila melanogaster: Selection for repellent insensitivity

Summary In a Y-unit maze wild-type flies of Drosophila melanogaster were tested for their chemotactic behavior reactions to insect repellents. Selection over 12 generations in two parallel experiments yielded two insensitive lines. Crosses indicated that the genes that were responsible for insensitivity were at least in part dominant. Lines selected for insensitivity to one repellent were also insensitive to a second repellent.     

Mechanism of activation of Sepharose and Sephadex by cyanogen bromide

The mechanism of CNBr activation of polysaccharide resins like Sepharose and Sephadex has been elucidated using recently published analytical procedures for the determination of cyanate esters and imido carbonates. It was found that on agarose-based resins coupling of ligand occurs predominantly via cyanate esters, and not via imidocarbonates as in the case of Sephadex. This explains the different behaviours of Sepharose and Sephadex during CNBr activation.