Abstract
Vertebrate brain development depends on a complex program of cell proliferation and migration. Post-mitotic neuronal migration in the developing cerebral cortex involves Nesprin-2, which recruits cytoplasmic dynein, kinesin, and actin to the nuclear envelope (NE) in other cell types. However, the relative importance of these interactions in neurons has remained poorly understood. To address these issues, we performed in utero electroporation into the developing rat brain to interfere with Nesprin-2 function. We find that an ∼100-kDa "mini" form of the ∼800-kDa Nesprin-2 protein, which binds dynein and kinesin, is sufficient, remarkably, to support neuronal migration. In contrast to dynein's role in forward nuclear migration in these cells, we find that kinesin-1 inhibition accelerates neuronal migration, suggesting a novel role for the opposite-directed motor proteins in regulating migration velocity. In contrast to studies in fibroblasts, the actin-binding domain of Nesprin-2 was dispensable for neuronal migration. We find further that, surprisingly, the motor proteins interact with Nesprin-2 through the dynein/kinesin "adaptor" BicD2, both in neurons and in non-mitotic fibroblasts. Furthermore, mutation of the Nesprin-2 LEWD sequence, implicated in nuclear envelope kinesin recruitment in other systems, interferes with BicD2 binding. Although disruption of the Nesprin-2/BicD2 interaction severely inhibited nuclear movement, centrosome advance proceeded unimpeded, supporting an independent mechanism for centrosome advance. Our data together implicate Nesprin-2 as a novel and fundamentally important form of BicD2 cargo and help explain BicD2's role in neuronal migration and human disease.