Membrane shrinkage and cortex remodelling are predicted to work in harmony to retract blebs.

Thomas E Woolley,Eamonn A Gaffney,Alain Goriely

doi:10.1098/rsos.150184

Abstract

Numerous cell types undergo an oscillatory form of dynamics known as blebbing, whereby pressure-driven spherical protrusions of membrane (known as blebs) expand and contract over the cell's surface. Depending on the cell line, blebs play important roles in many different phenomena including mitosis and locomotion. The expansion phase of cellular blebbing has been mathematically modelled in detail. However, the active processes occurring during the retraction phase are not so well characterized. It is thought that blebs retract because a cortex reforms inside, and adheres to, the bleb membrane. This cortex is retracted into the cell and the attached bleb membrane follows. Using a computational model of a cell's membrane, cortex and interconnecting adhesions, we demonstrate that cortex retraction alone cannot account for bleb retraction and suggest that the mechanism works in tandem with membrane shrinking. Further, an emergent hysteresis loop is observed in the intracellular pressure, which suggests a potential mechanism through which a secondary bleb can be initiated as a primary bleb contracts.

Highlights

Many animal cells have the ability to produce large, dynamic protrusions such as lamellae, filopods, microspikes and pseudopods [1]
We are interested in a specific protrusion type known as a cellular bleb, which plays an important role in the locomotion of tumour cells, embryonic cells and stem cells [4,5,6,7]
Extensive mathematical modelling work has been performed on the expansion phase of cell protrusions known as blebs

Summary

Introduction

Many animal cells have the ability to produce large, dynamic protrusions such as lamellae, filopods, microspikes and pseudopods [1]. Each of these four protrusion types rely on the polymerization of actin filaments in order to push the cell membrane outwards. Often, cells use these membrane extensions to undergo motility [2]; they can be involved in a number of other different phenomena, such as mitosis [3].

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