Optimal orientation in branched cytoskeletal networks

TL;DR

This paper presents a kinetic-population model of actin filament orientation in lamellipodia, explaining observed filament orientation peaks and addressing filament overlap phenomena in cytoskeletal networks.

Contribution

It introduces a new model incorporating orientational-dependent branching and capping, providing insights into filament orientation distributions and their spatial organization.

Findings

Model explains two characteristic filament orientation peaks.

Incorporates a subdominant filament population for better data fit.

Addresses filament overlap observations conflicting with existing models.

Abstract

Actin cytoskeletal protrusions in crawling cells, or lamellipodia, exhibit various morphological properties such as two characteristic peaks in the distribution of filament orientation with respect to the leading edge. To understand these properties, using the dendritic nucleation model as a basis for cytoskeletal restructuring, a kinetic-population model with orientational-dependent branching (birth) and capping (death) is constructed and analyzed. Optimizing for growth yields a relation between the branch angle and filament orientation that explains the two characteristic peaks. The model also exhibits a subdominant population that allows for more accurate modeling of recent measurements of filamentous actin density along the leading edge of lamellipodia in keratocytes. Finally, we explore the relationship between orientational and spatial organization of filamentous actin in lamellipodia and address recent observations of a prevalence of overlapping filaments to branched filaments---a finding that is claimed to be in contradiction with the dendritic nucleation model.