Patterning of membrane adhesion under hydraulic stress

Lumen formation is ubiquitous in developmental biology. The successful opening of fluid filled spaces within tissues is crucial for a zygote to grow into a topologically complex adult organism containing multiple cavities and networks of tubes. These cavities often form by the coarsening of microlumens. For instance, during blastulation in the early development of animals, embryos undergo a dynamic transformation from the morula, a dense ball of cells, to the blastula, a hollow sphere surrounding a pressurized fluid-filled cavity. This process starts with the accumulation of fluid due to ionic pumping in hundreds of micro-lumens that fracture cell-cell contacts. Later, these micro-lumens discharge into a dominant lumen in a coarsening process. However, how these microlumens nucleate and coarsen is still poorly understood. To address this issue, we look at the formation of microlumens and their progressive coarsening in the adhesion of giant unilamellar vesicles adhered to a supported lipid bilayer after an osmotic shock. Together with a theoretical model and a computational framework, we explore the length- and time-scales relevant to this process. We show the main ingredients leading to nucleation, the shape of the resulting lumens, and their coarsening.