Nuclear movement is critical for developmental events, cell polarity, and migration and is usually mediated by linker of nucleoskeleton and cytoskeleton (LINC) complexes connecting the nucleus to cytoskeletal elements. Compared to active nuclear movement, relatively little is known about homeostatic positioning of nuclei, including whether it is an active process. To explore homeostatic nuclear positioning, we developed a method to displace nuclei in adherent cells using centrifugal force. Nuclei displaced by centrifugation rapidly recentered by mechanisms that depended on cell context. In cell monolayers with wounds oriented orthogonal to the force, nuclei were displaced toward the front and back of the cells on the two sides of the wound. Nuclei recentered from both positions, but at different rates and with different cytoskeletal linkage mechanisms. Rearward recentering was actomyosin, nesprin-2G, and SUN2 dependent, whereas forward recentering was microtubule, dynein, nesprin-2G, and SUN1 dependent. Nesprin-2G engaged actin through its N terminus and microtubules through a novel dynein interacting site near its C terminus. Both activities were necessary to maintain nuclear position in uncentrifuged cells. Thus, even when not moving, nuclei are actively maintained in position by engaging the cytoskeleton through the LINC complex.
Keywords: KASH; LINC complex; SUN; actin; centrifugation; dynein; homeostatic nuclear positioning; microtubules; nesprin-2.
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