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P011 The nuclear pore complex protein NDC 1 is involved in nuclear positioning in migrating fibroblasts Daniel S. Osorio, Joana Borrego-Pinto and Edgar R. Gomes Université Pierre et Marie Curie (Paris 6), Paris, France Positioning of the nucleus within cells has a role in different processes such as cell migration and muscle differentiation. In migrating fibroblasts the nucleus moves backwards prior to cell migration and this active movement is dependent on the actin cytoskeleton and on nuclear envelope proteins members of the LINC complex Nesprin-2 and SUN2. In order to identify novel proteins involved in this process we preformed a live-imaging screen for inhibition of nuclear movement through RNA interference (RNAi) against a set of 230 potential/confirmed nuclear envelope proteins from published organellar proteomics studies. NDC1, a conserved transmembrane protein of the nuclear pore complex (NPC) was one of our hits. The screening results were further confirmed by the inhibition of centrosome reorientation and nuclear positioning in a fixed cell assay. Although a full knock down of Ndc1 caused general disruptions of the nuclear envelope, consistent with its role in nuclear pore assembly, a partial knockdown was sufficient to inhibit nuclear movement without significantly affecting nuclear envelope proteins and structure. Furthermore we identified a specific interaction between the N-terminal region of Ndc1 and SUN2, distinct from the proposed NPC interacting region on the conserved C-terminus. Given that SUN2 and NPC do not seem to co-localize in the NE, we propose that a subpopulation of non-NPC Ndc1 is involved in stabilizing SUN2 during nuclear movement