  Protrusions at the leading-edge of a cell play an important role in sensing
the extracellular cues, during cellular spreading and motility. Recent studies
provided indications that these protrusions wrap (coil) around the
extra-cellular fibers. The details of this coiling process, and the mechanisms
that drive it, are not well understood. We present a combined theoretical and
experimental study of the coiling of cellular protrusions on fibers of
different geometry. Our theoretical model describes membrane protrusions that
are produced by curved membrane proteins that recruit the protrusive forces of
actin polymerization, and identifies the role of bending and adhesion energies
in orienting the leading-edges of the protrusions along the azimuthal (coiling)
direction. Our model predicts that the cell's leading-edge coils on round
fibers, but the coiling ceases for a fiber of elliptical (flat) cross-section.
These predictions are verified by 3D visualization and quantitation of coiling
on suspended fibers using Dual-View light-sheet microscopy (diSPIM). Overall,
we provide a theoretical framework supported by high spatiotemporal resolution
experiments capable of resolving coiling of cellular protrusions around
extracellular fibers of varying diameters.

Biological Physics;Soft Condensed Matter