Morphodynamic profiling of protrusion phenotypes

¹ The Scripps Research Institute

^* To whom correspondence should be addressed. E-mail: gdanuser{at}scripps.edu.

Submitted on August 9, 2005
Revised on September 13, 2005
Accepted on 7 November 2005

	Abstract

We propose a framework for tracking arbitrary complex cell boundary movements, relying on a unique definition of protrusion and retraction as the path length a virtual edge marker traverses when moving continuously perpendicular to the cell boundary. We introduce the Level Set Method as a numerical scheme to reconstruct continuous boundary movement in time-lapse image sequences with finite time sampling. For moderately complex movements, we describe a numerically less expensive method which satisfactorily approximates the definition. Densely sampled protrusion and retraction rates were accumulated in space-time charts revealing distinct morphodynamic states. Applying this technique to the profiling of epithelial cell protrusion we identified three different states. In the I-state, long cell edge sectors are synchronized in cycles of protrusion and retraction. In the V-state random bursts of protrusion initiate protrusion waves propagating transversally in both directions. Cells switch between both states dependent on the Rac1 activation level. Furthermore, the persistence of V-state transversal waves depends on Arp2/3 concentration. Inhibition of PAK shifts cells into a -state where continuous protrusion is occasionally interrupted by self-propagating ruffles. Our data supports a model where activation of Rac1 mediates the propagation of protrusion waves, whose persistence depends on the relative abundance of activated Arp2/3 and polymerizable G-actin.

Key Words: Cell Migration, Edge Tracking, Level Set Method, Morphology Dynamics, Protrusion Activity Map