Abstract
Nuclei migrate during many events, including fertilization, establishment of polarity, differentiation, and cell division. The Caenorhabditis elegans KASH protein UNC-83 localizes to the outer nuclear membrane where it recruits kinesin-1 to provide the major motor activity required for nuclear migration in embryonic hyp7 cells. Here we show that UNC-83 also recruits two dynein-regulating complexes to the cytoplasmic face of the nucleus that play a regulatory role. One consists of the NudE homolog NUD-2 and the NudF/Lis1/Pac1 homolog LIS-1, and the other includes dynein light chain DLC-1, the BicaudalD homolog BICD-1, and the Egalitarian homologue EGAL-1. Genetic disruption of any member of these two complexes caused nuclear migration defects that were enhanced in some double mutant animals, suggesting that BICD-1 and EGAL-1 function in parallel to NUD-2. Dynein heavy chain mutant animals also had a nuclear migration defect, suggesting these complexes function through dynein. Deletion analysis indicated that independent domains of UNC-83 interact with kinesin and dynein. These data suggest a model where UNC-83 acts as the cargo-specific adaptor between the outer nuclear membrane and the microtubule motors kinesin-1 and dynein. Kinesin-1 functions as the major force generator during nuclear migration, while dynein is involved in regulation of bidirectional transport of the nucleus.