Abstract
One of the grand challenges of bottom-up synthetic biology is the development of minimal machineries for cell division. The mechanical transformation of large-scale compartments, such as Giant Unilamellar Vesicles (GUVs), requires the geometry-specific coordination of active elements, several orders of magnitude larger than the molecular scale. Of all cytoskeletal structures, large-scale actomyosin rings appear to be the most promising cellular elements to accomplish this task. Here, we have adopted advanced encapsulation methods to study bundled actin filaments in GUVs and compare our results with theoretical modeling. By changing few key parameters, actin polymerization can be differentiated to resemble various types of networks in living cells. Importantly, we find membrane binding to be crucial for the robust condensation into a single actin ring in spherical vesicles, as predicted by theoretical considerations. Upon force generation by ATP-driven myosin motors, these ring-like actin structures contract and locally constrict the vesicle, forming furrow-like deformations. On the other hand, cortex-like actin networks are shown to induce and stabilize deformations from spherical shapes.
Highlights
One of the grand challenges of bottom-up synthetic biology is the development of minimal machineries for cell division
These experiments have extended to actin–membrane interactions, including reconstitution of actin cortices on the outside of giant unilamellar vesicles (GUVs)[16,17,18], and contractile actomyosin networks associated with supported membranes[19,20,21]
In order to investigate the interplay between actin cross-linking and membrane binding, we used a modified continuous droplet interface crossing encapsulation (cDICE) method[45,46] to encapsulate G-actin with associated proteins and generate cytoskeletal Giant Unilamellar Vesicles (GUVs) made from the lipid POPC (Fig. 1a)
Summary
One of the grand challenges of bottom-up synthetic biology is the development of minimal machineries for cell division. Actin filaments are organized into cross-linked, branched, and bundled networks These different architectures appear in structures, such as filopodia, stress fibers, the cell cortex, and contractile actomyosin rings; each has unique physical properties and fulfills different roles in important cellular processes[1]. The focus of actinrelated work has since shifted from identifying the components responsible for muscle contraction[11], to investigating more detailed aspects of the cytoskeleton[8,12], such as the dynamics of actin assembly[13,14] or the cross-talk with other cytoskeletal elements[15] These experiments have extended to actin–membrane interactions, including reconstitution of actin cortices on the outside of giant unilamellar vesicles (GUVs)[16,17,18], and contractile actomyosin networks associated with supported membranes[19,20,21]. Creating a synthetic cell with minimal components recapitulating crucial life processes, such as self-organization, homeostasis, and replication, has become an attractive goal[22,23]
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