PKC-dependent ERK phosphorylation is essential for P2X7 receptor-mediated neuronal differentiation of neural progenitor cells.

Purinergic receptors have been shown to be involved in neuronal development, but the functions of specific subtypes of P2 receptors during neuronal development remain elusive. In this study we investigate the distribution of P2X7 receptors (P2X7Rs) in the embryonic rat brain using in situ hybridization. At E15.5, P2X7R mRNA was observed in the ventricular zone and subventricular zone, and colocalized with nestin, indicating that P2X7R might be expressed in neural progenitor cells (NPCs). P2X7R mRNA was also detected in the subgranular zone and dentate gyrus of the E18.5 and P4 brain. To investigate the roles of P2X7R and elucidate its mechanism, we established NPC cultures from the E15.5 rat brain. Stimulation of P2X7Rs induced Ca(2+) influx, inhibited proliferation, altered cell cycle progression and enhanced the expression of neuronal markers, such as TUJ1 and MAP2. Similarly, knockdown of P2X7R by shRNA nearly abolished the agonist-stimulated increases in intracellular Ca(2+) concentration and the expression of TUJ1 and NeuN. Furthermore, stimulation of P2X7R induced activation of ERK1/2, which was inhibited by the removal of extracellular Ca(2+) and treatment with blockers for P2X7R and PKC activity. Stimulation of P2X7R also induced translocation of PKCα and PKCγ, but not of PKCß, whereas knockdown of either PKCα or PKCγ inhibited ERK1/2 activation. Inhibition of PKC or p-ERK1/2 also caused a decrease in the number of TUJ1-positive cells and a concomitant increase in the number of GFAP-positive cells. Taken together, the activation of P2X7R in NPCs induced neuronal differentiation through a PKC-ERK1/2 signaling pathway.

Nonequilibrium relaxation times in polymer knot groups.

Flexible polymer knots with strict topological constraint of no segment crossing are studied by Monte Carlo simulations. The nonequilibrium relaxation time of an equilibrated polymer knot cut at one point to relax to a linear chain is measured. Prime knots up to 20 essential crossings from the groups (3(1),5(1),7(1),...), (4(1),6(1),8(1),...) and (5(2),7(2),9(2),...), (6(2),8(2),10(2),...) are studied. The nonequilibrium relaxation time for knots within a group are found to increase stepwise linearly with the number of essential crossings of the original knot. Our results suggest an equally spaced topological interaction energy spectrum for knots in the same group and thus provide a quantitative description of topological interactions.

Translation drag coefficient of a self-similar assembly of spheres immersed in an incompressible fluid.

On the basis of deterministic fractals and the Rotne-Prager hydrodynamic interaction tensor, we confirm the asymptotic as well as the finite size scaling of the friction coefficient lambda of a self-similar structure. The fractal assembly is made of N spheres with its dimension varying from D < 1 to D = 3. The number of spheres can be as high as N approximately O(10(4)). The asymptotic scaling behavior of the friction coefficient per sphere is lambda approximately N(1/D-1) for D > 1, lambda approximately (lnN)(-1) for D = 1, and lambda approximately N(0) for D < 1. The crossover behavior indicates that while in the regime of D > 1 the hydrodynamic screening effect grows with the size, for D<1 it is limited in a finite range, which decays with decreasing D.

Dynamic modelling of the growth of a surface fungal colony.

The growth of a surface fungal colony in the three-dimensional space was modeled kinetically. The present analysis led to the conclusion that the radius of a fungal colony increases exponentially in the initial period followed by a constant increase in its radius at large times. This is justified by analyzing the available experimental data. The elevation of a fungal colony was limited by a balance of the transport of protoplasm inside a growing hyphae and a maintenance factor. A numerical simulation revealed that a typical fungal colony had a disk-shaped base with a flat top and a side face generated by rotating a concave upward curve about a vertical axis.