Extracellular Cues Govern Shape and Cytoskeletal Organization in Giant Unilamellar Lipid Vesicles

Spontaneous and induced
front-rear polarization and a
subsequent
asymmetric actin cytoskeleton is a crucial event leading to cell migration,
a key process involved in a variety of physiological and pathological
conditions such as tissue development, wound healing, and cancer.
Migration of adherent cells relies on the balance between adhesion
to the underlying matrix and cytoskeleton-driven front protrusion
and rear retraction. A current challenge is to uncouple the effect
of adhesion and shape from the contribution of the cytoskeleton in
regulating the onset of front-rear polarization. Here, we present
a minimal model system that introduces an asymmetric actin cytoskeleton
in synthetic cells, which are resembled by giant unilamellar lipid
vesicles (GUVs) adhering onto symmetric and asymmetric micropatterned
surfaces. Surface micropatterning of streptavidin-coated regions with
varying adhesion shape and area was achieved by maskless UV photopatterning.
To further study the effects of GUV shape on the cytoskeletal organization,
actin filaments were polymerized together with bundling proteins inside
the GUVs. The micropatterns induce synthetic cell deformation upon
adhesion to the surface, with the cell shape adapting to the pattern
shape and size. As expected, asymmetric patterns induce an asymmetric
deformation in adherent synthetic cells. Actin filaments orient along
the long axis of the deformed GUV, when having a length similar to
the size of the major axis, whereas short filaments exhibit random
orientation. With this bottom-up approach we have laid the first steps
to identify the relationship between cell front-rear polarization
and cytoskeleton organization in the future. Such a minimal system
will allow us to further study the major components needed to create
a polarized cytoskeleton at the onset of migration.