Colocalization of TD-60 and INCENP throughout G2 and mitosis: evidence fortheir possible interaction in signalling cytokinesis

TD-60 and INCENP are two members of the chromosome passenger protein family , and each has been suggested to play a role in the control of cytokinesis. Here we demonstrate by confocal immunofluorescence microscopy that TD-60 a nd INCENP distribute identically throughout the cell cycle. Both appear coo rdinately in G2-phase nuclei and become concentrated at centromeres during prophase. TD-60 and INCENP both then leave the chromosome together during a naphase and redistribute to the spindle midzone, as do other chromosome pas senger proteins, and traverse the entire equatorial diameter from cortex to cortex. By image overlay and pixel count analysis we show that TD-60 and I NCENP are distinct among known chromosome passenger proteins in extending b eyond the spindle to the cortex. Further, we show that the cytokinesis-asso ciated protein kinase AIM-1 also shares this distribution property. We sugg est that this redistribution is required to signal cytokinesis. TD-60 and I NCENP also show identical localization in cells that exit mitosis in the pr esence of dihydrocytochalasin B (DCB), an inhibitor of actin assembly. Such cells can resume cleavage upon removal of DCB and in a recovery subpopulat ion that cleaves only on one side, these proteins both colocalize to the co rtex only where a cleavage furrow forms. Given the coincident distribution of TD-60 and INCENP during both interphase and mitosis, we suggest that the se proteins may cooperate, perhaps within a protein complex, in signalling cytokinesis. Such a mechanism, using chromosome passenger proteins, may ens ure that cytokinesis occurs only between the separated chromatids, and only after they have segregated.