Liquid-like condensates mediate competition between actin branching and bundling.

Reorganization of actin filaments allows cells to migrate, which is required for embryonic development, wound healing, and cancer metastasis. During migration, the leading-edge of the cell consists of needle-like protrusions of bundled actin, which emanate from a sheet of branched actin. Given that the proteins responsible for both architectures are present simultaneously, what determines whether actin filaments will be branched or bundled? Here we show that liquid-like condensates, composed of both branching and bundling proteins, can mediate the inherent competition between these fundamentally different ways of organizing actin networks. This work demonstrates that by tuning the composition of condensates, we can recapitulate the transition from branched to bundled networks, a key step in cell migration.