Condensate-mediated shape transformations of cellular membranes by capillary forces

TL;DR

This study investigates how biomolecular condensates influence membrane shape changes in cells, revealing the roles of interfacial tension and energy barriers in forming tubes, sheets, and cups, with implications for cellular organization.

Contribution

The paper combines live-cell imaging, in vitro reconstitution, and simulations to elucidate the mechanisms of condensate-driven membrane morphogenesis and shape transitions.

Findings

High interfacial tension stabilizes sheet structures.

Lower tension favors tube and cup formations.

Shape transitions exhibit hysteresis influenced by membrane history.

Abstract

Phase-separated biomolecular condensates with liquid-like properties play a key role in the organization and compartmentalization of the intracellular environment. Condensate-mediated capillary forces acting on membranes drive physiologically important reshaping of membrane-bound organelles, such as vacuoles and autophagosomes. Here, we explore condensate-mediated membrane shape transformations. We employ {\textit{in planta}} live-cell imaging, an \textit{in vitro} reconstitution system with tunable interfacial tension, and computer simulations of an elastic membrane model to describe three morphologies of membrane structures localized at condensate interfaces: tubes, sheets, and cups. We find that the forces associated with high interfacial tension drive the formation of stable sheets, while tubes and cups prevail at lower interfacial tension. We calculate the free energies of each membrane shape and identify the energy barriers that govern the transitions between the shapes. With this approach, we find that shape transformations depend on the history of the interfacial membrane and exhibit a tube-to-cup hysteresis. These findings indicate that temporal control of condensate surface properties can mediate the morphogenesis of cup-like structures in cells, such as the formation of "bulbs" within plant vacuoles. Our results further generalize how the interplay of condensates and membranes contributes to intracellular organization.