nud-1 is the C. elegans ortholog of the Aspergillus nidulans gene nudC, originally identified in a screen for proteins affecting nuclear positioning within the hyphae. Our lab has previously shown functional conservation between nudC and
nud-1. Mammalian nudC encodes a protein that interacts with Lis-1, a gene product essential for neuronal migration in the developing mammalian brain. Expression of C. elegans
nud-1 was found in the neurons, gonad, gut, vulva, hypodermis, and embryos. Mammalian NudC has also been shown to interact with dynein and to colocalize with
p150dynactin and gamma tubulin. We have previously described the phenotypes resulting from injection of
nud-1 dsRNA. Embryonic lethality occurs, wherein the primary visible phenotype in one-celled embryos is a defect in pronuclear rotation. Following pronuclear meeting, rotation onto the longitudinal axis does not occur, reminiscent of the
p150glued phenotype. Oogenesis fails rapidly after injection of
nud-1 dsRNA, preventing an examination of potentially stronger embryonic phenotypes. We have utilized the technique of RNAi feeding to more thoroughly examine the embryonic phenotypes associated with
nud-1 knockdown.
nud-1(RNAi) feeding yields not only the phenotypes discussed above, but also additional defects in the one-celled embryo. In NUD-1 depleted embryos, a spindle developed and elongated along the longitudinal axis, and the cleavage furrow appears at the appropriate time and position. However, the cleavage furrow in the
nud-1 RNAi embryo stalls and regresses quickly, resulting in a multinucleated one-celled embryo. Additionally, in 10% of the embryos centrosome over-replication occurs during pronuclear migration, resulting in multipolar spindles. Each MTOC nucleates microtubules, resulting in multiple cytokinetic furrows, some of which regress before the next cell division. To further examine the late cytokinesis failure in the
nud-1 RNAi embryos, we determined whether midzone microtubules were present. Central spindles, viewed by anti-tubulin staining, often appear reduced (74%) or absent (26%) in these embryos. Correlating with these defects, AIR-2, a protein proposed to be required for cytokinesis, is mislocalized in
nud-1(RNAi) embryos. Additionally, chromosomes are missegregated following these events. These results indicate an important function for NUD-1 during cytokinesis during C. elegans early embryonic development, a case strengthened by mammalian data demonstrating both interaction and localization with spindle components.