Unstable membrane outgrowth induced by filament tip spreading

We analyse the dynamics of a network of regularly spaced parallel filaments , growing perpendicularly against an elongating membrane which limits the d iffusion of monomers in the half-space where filaments grow. When the membr ane bulges, some filaments spread, so that less monomers are absorbed at th e bulge periphery. It results in both a local increase of the free monomer concentration and an enhancement of the filament polymerisation rate, leadi ng to an original growth instability. This one, stabilised here at short wa velengths by filament tip diffusion along the membrane and the drawback for ce exerted by a subjacent network of crosslinking molecules, may play a not iceable pact in the initiation of neuritic and lamellipodial structures. (C ) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier S AS.