BAF takes the lead in NE formation

The assembly of the nuclear envelope (NE) during telophase is a key step in mitosis, and mutations in NE proteins lead to several diseases – the nuclear laminopathies. The DNA-binding protein BAF is thought to have an important role in NE formation, but the dynamics of this process in vivo are not well understood. Tokuko Haraguchi and colleagues previously showed that BAF accumulates at the `core' region – the area of the telophase chromosome mass that sits close to the microtubules (MTs) of the mitotic spindle. Now, on page 2540, the authors show that BAF (as a GFP-fusion protein) accumulates at the core region earlier than several other NE proteins (including lamin A and emerin) and, once there, interacts directly with lamin A, emerin and itself. Moreover, FRAP analysis indicates that BAF-GFP at the core region is highly immobile, and electron microscopy shows that BAF forms an electron-dense structure on telophase chromosomes. When BAF is knocked down, the authors show, NE formation is perturbed; in addition, BAF does not assemble at the core when cells are treated with the MT-depolymerising reagent nocodazole. The authors propose a model in which BAF assembles in an MT-dependent manner and recruits NE precursor vesicles that contain other core-region proteins. Their data have implications for the treatment of nuclear laminopathies.