Self Organization in Cells - How to Use Proteins to Solve a Geometry Problem

Fragments of fish pigment cells can form and center aggregates of
pigment granules by dynein-motor-driven transport along a
self-organized radial array of microtubules (MTs). I will present a
quantitative model that describes pigment aggregation and MT-aster
self-organization and the subsequent centering of both structures.
The model is based on the observations that MTs are immobile and
treadmill, while dynein-motor-covered granules have the ability to
nucleate MTs. From assumptions based on experimental observations,
I'll derive partial integro-differential equations describing the
coupled granule-MT interaction. Analysis explains the mechanism of
aster self-organization as a positive feedback loop between motor
aggregation at the MT minus ends and MT nucleation by motors.
Furthermore, the centering mechanism is explained as a global
geometric bias in the cell established by spontaneously-nucleated
microtubules. Numerical simulations lend additional support to the
analysis. The model sheds light on role of polymer dynamics and
polymer-motor interactions in cytoskeletal organization.