In C.elegans, U-shaped gonads are formed by directed migration of gondal distal tip cells (DTCs). Cytoskeletal regulation appears to be one of the important processes to regulate DTC migration, but its molecular mechanism remains elusive. The
vab-10 gene encodes spectraplakins, cytoskeletal linker proteins, and the
vab-10(
tk27) mutant exhibits abnormal gonad formation due to the defective DTC migration. Complementation tests, Western blot, and immunohistochemical analyses revealed that this mutation results in the loss of DTC-specific VAB-10B isoform(s). When wild type DTCs turn dorsally, the rotation of migratory axis from anteroposterior to dorsoventral is preceded by nuclear migration within DTCs. However,
vab-10(
tk27) inhibited this nuclear migration. Although DTCs are attracted dorsally by the UNC-6/netrin guidance in the mutants, their nuclei stayed at their anterior or posterior ends rather than were relocated to the dorsal side of DTCs as in the wild type, suggesting that VAB-10B is required for nuclear migration of DTCs in response to the UNC-6 signal. In
vab-10(
tk27), although the alignment of F-actins was affected mildly, that of microtubules was severely disorganized. Interestingly, a
vab-10 mini gene encoding only the actin-binding domain fused with the microtubule-binding domain was sufficient to rescue the mutant phenotype, suggesting the activity of VAB-10 in linking actin and microtubule cytoskeletons. Because the KASH protein UNC-83 interacts with the SUN protein UNC-84 in the nuclear membrane and recruits kinesin-1 to regulate nuclear migration in embryonic
hyp7 cells, we examined migration of the DTC nuclei in the
unc-83 and
unc-84 mutants. We found that nuclear relocation in the DTCs at the first turn is compromised as in the
vab-10(
tk27) mutants. We propose that VAB-10B/spectraplakin acts to regulate the alignment of microtubules by linking F-actins and microtubules in DTCs, which may facilitate proper alignment of microtubules along which the nuclei are translocated in a kinesin-dependent manner.