Nuclear migration and anchorage are essential for a number of cellular and developmental events, such as fertilization, cell migration, establishment of polarity, and cell division. Defects in nuclear migration events have been linked to the human diseases Emery-Dreifuss muscular dystrophy and lissencephaly. In wild type, embryos
hyp7 precursor nuclei migrate contra laterally across the dorsal midline. In
unc-83 and
unc-84 mutants, nuclear migration fails and nuclei are positioned in the dorsal cord. In
unc-83(
e1408) null animals, we observe 11.8 plus or minus 0.1 nuclei in the dorsal cord. UNC-83 and UNC-84 form a bridge across the nuclear envelope, transferring force required for nuclear migration from the cytoskeleton to the nuclear lamina. The C-terminal KASH domain of UNC-83 interacts with the SUN domain of UNC-84 in the perinuclear space, while the N-terminal region of the protein extends into the cytosol (McGee et al. 2006). To elucidate the role of the cytosolic portion of UNC-83, I performed a yeast-two-hybrid screen. The screen identified 45 potential interacting partners, including KLC-2, which was pulled out twelve times. KLC-2 interacts with the kinesin heavy chain protein UNC-116 to form a homologue of the mammalian conventional kinesin (Sakamoto et al. 2005). The null allele
klc-2(
km28) results in L1 arrest. A hypomorphic allele (
km11), which consists of a large deletion in the endogenous
klc-2 locus and an insertion of a partial second copy of the gene, is viable but has 7.3 plus or minus 0.2
hyp7 nuclei in the dorsal cord. Furthermore, rare escaper (
km28) animals that could be analyzed for
hyp7 migration prior to arrest have 10.4 plus or minus 0.7 nuclei in the dorsal cord. Immunofluorescence with a rabbit polyclonal antibody to KLC-2, generously provided by Frank McNally (Yang et al. 2005), indicates that KLC-2 is expressed in wild type and the
km11 mutant
hyp7 cells in a pattern indicative of exclusion from the nucleus and at least some co-expression with UNC-83. Expression in
km11 mutants appears fainter and more punctate compared to wild type. Amino acids 137-362 of UNC-83 were sufficient to interact with KLC-2 using a directed yeast-two-hybrid approach. These data suggest a model in which UNC-83 functions as a cargo specific adapter to recruit kinesin to the nuclear envelope, where it generates the major force required to move the nucleus. Future work to test this model includes characterization of the
km11 allele as well as the construction of a KLC-2-KASH construct, which we predict will target to the nuclear membrane and rescue nuclear migration in
unc-83 mutants.