Flip Flop-Associated Growth and Division of Synthetic Cells.

Cells grow their boundaries by incorporating newly synthesized lipids into their membranes as well as through fusion of intracellular vesicles. As these processes yield trans-bilayer imbalances in lipid numbers, cells must redistribute lipids across the bilayer to enable sustained growth. Using giant and large unilamellar vesicles (GUVs and LUVs, respectively), we here recapitulate cellular growth and division under various conditions of transmembrane 'flip flop' of lipids. By dynamically monitoring the changes in reduced volume, spontaneous curvature, and area difference of GUVs that grow by fusion of many small LUVs, the morphology of these growing 'synthetic cells' is quantified. We demonstrate, for membranes containing various flip flop-capable molecules, that curvature stresses are relieved, generating more symmetrically sized buds, without significantly compromising the membrane integrity. Further increasing the neck curvature is shown to lead to bud scission. The mechanisms presented here offer insights into cell growth and division, which are important for understanding early protocells and designing synthetic cells that are able to grow and divide.