A. Boulbitch et al., Shape instability of a biomembrane driven by a local softening of the underlying actin cortex, PHYS REV E, 62(3), 2000, pp. 3974-3985
We present a theory showing that local shape instabilities of composite bio
logical membranes, consisting of a lipid bilayer and an underlying actin co
rtex, can be triggered by a local softening, of the membrane-associated cyt
oskeleton. A membrane containing such cortical defects can form blisters or
invaginations, depending on external conditions. The theoretical predictio
ns agree with observations provided by two sets of experiments: (i) microsc
opic observations of shape changes of giant vesicles with underlying shells
of a thin actin network show the formation of local blisters and (ii) micr
opipet aspiration experiments of Dictyostelium discoideum cells in which we
observed the formation of blisters in the aspirated cell part. In the latt
er experiments, the existence of a hole in the underlying cortex is confirm
ed by observation of the entrance of cell organelles into the blister. Our
model may also be applied to the formation of lobopodia, fast-growing cell
protrusions that play an important role in the locomotion and spreading of
biological cells.