Human KASH and SUN domains are functional for C. elegans hypodermal nuclear migration. (A) Luminal domains of hSUN1 and Nesprin-4 (checkered shading) were fused to the nucleoplasmic and cytoplasmic domains of C. elegans UNC-84 and UNC-83 (solid shading), respectively. A C-terminal GFP was added to UNC-84/hSUN1 constructs. The transmembrane span (TM) is in black. (B) Mean number of dorsal cord nuclei in transgenic L1 larvae. Error bars denote standard deviations. For UNC-84/hSUN1(Δ616–620), three independent transgenic lines were assayed; data from one representative line are shown. (C and C′) Immunofluorescence of transgenic unc-84; unc-83 double mutant embryos with anti-GFP and anti–UNC-83 antibodies showed that both chimeric proteins were localized to the NE. (D and D′) Deletion of residues corresponding to 616–620 of the predicted trimerization domain of hSUN1 does not prevent localization of UNC-84/hSUN1 to the NE (D), but UNC-83/hNesprin-4 fails to localize (D′). Arrows indicate hyp7 nuclei that are positive for UNC-83 (C′) or missing UNC-83 (D′). For all images, anterior is left, and dorsal is up. Bar, 10 µm.