Nuclear envelope (NE) budding was recently shown to facilitate transport of large complexes between the nucleus and the cytoplasm; these structures are encapsulated by the inner nuclear membrane, which then fuses with the outer nuclear membrane and so aids translocation of the macromolecules. Although the sequence of events has been defined, the underlying mechanisms are still poorly understood. Susan Parkhurst and colleagues have previously observed that the Wiskott–Aldrich Syndrome protein Wash localises to the nucleus and interacts with Lamin B. Now (Verboon et al., 2020), they identify Wash, along with its four-subunit regulatory complex SHRC, as crucial components of the NE budding pathway. Drosophila wash mutants have fewer NE buds, as do those where any of the SHRC components have been knocked down. Interestingly, wash mutants display wrinkled nuclei resulting from a disorganised Lamin network, which is not observed in SHRC-knockdown flies. This points to a dual role for Wash in NE budding: a structural role in nuclear morphology and Lamin mesh stability, and a mechanical role in bud formation, which is dependent on SHRC. Furthermore, the actin-nucleation activity of Wash that is required for budding results from its interaction with Arp2/3 and also involves capping protein. Therefore, this study provides new insights into the molecular mechanism of NE budding and uncovers a role for the cytoskeletal machinery in controlling nuclear bud formation.
