Ioannis Lelidis | PubMed Health

PubMed2004

Defect dynamics in a smectic Grandjean-Cano wedge.

An array of edge dislocation forms spontaneously in a Grandjean-Cano wedge filled by a smectic liquid crystal. In the vicinity of the smectic A to smectic C transition, these defects are visible under the microscope [R. B. Meyer, B. Stebler, and S. T. Lagerwall, Phys. Rev. Lett. 41, 1393 (1978)]. This paper deals with their dynamics under controlled deformation (dilation and compression). First, we characterize several regimes of dislocation mobility occurring with increasing strain epsilon or strain rate epsilon;. We relate these regimes to the interactions between screw and edge dislocations. We also show that screw dislocations give rise to loops of edge dislocations under sufficient strain, which strengthens the model of loop nucleation by helical instability of screw dislocations. Lastly, we discuss several models for the microscopic origin of the interactions between defects.

Journal Article↗

PubMed2003

The effect of diffusion, depolymerization and nucleation promoting factors on actin gel growth.

In eukaryotic cells, localized actin polymerization is able to deform the plasma membrane and push the cell forward. Depolymerization of actin filaments and diffusion of actin monomers ensure the availability of monomers at sites of polymerization, and therefore these processes must play an active role in cellular actin dynamics. Here we reveal experimental evidence that actin gel growth can be limited by monomer diffusion, consistent with theoretical predictions. We study actin gels formed on beads coated with ActA (and ActA fragments), the bacterial factor responsible for actin-based movement of Listeria monocytogenes. We observe a saturation of gel thickness with increasing bead radius, the signature of diffusion control. Data analysis using an elastic model of actin gel growth gives an estimate of 2x10(-8) cm(-2) s(-1) for the diffusion coefficient of actin monomers through the gel, ten times less than in buffer, and in agreement with literature values in bulk cytoskeleton, providing corroboration of our model. The depolymerization rate of actin filaments and the elastic modulus of the gel are also evaluated. Furthermore, we qualitatively examine the different actin gels produced when ActA fragments interact with either VASP or the Arp2/3 complex.

Actin-Related Protein 2↗