An aurora kinase homologue is involved in regulating both mitosis and cytokinesis in Trypanosoma brucei

The chromosomal passenger protein aurora kinases have been implicated in regulating chromosome segregation and cell division. Three aurora kinase homologues were identified (TbAUK1, -2 and -3) in the Trypanosome Genomic Data Base, and their expressions in the procyclic form of Trypanosoma brucei were knocked down individually by using the RNA interference technique. Only a knockdown of TbAUK1 arrested the cells in G(2)/M phase with each cell showing an extended posterior end, two kinetoplasts, and an enlarged nucleus, apparently the result of an inhibited kinetoplast multiplication and a failed mitosis. There is no mitotic spindle structure in the TbAUK1-depleted cell. The two kinetoplasts moved apart from each other but stopped just before cytokinesis, suggesting that cytokinesis was blocked in its early phase. Overexpression of TbAUK1 in the cells resulted in little change in cell growth. By immunofluorescence, TbAUK1 was primarily localized to the nucleus in interphase and to the mitotic spindle during apparent metaphase and anaphase. Thus, differing from other eukaryotes, TbAUK1 has an apparent triple function in coupling mitosis and kinetoplast replication with cytokinesis in T. brucei. T. brucei polo-like kinase, previously identified as the initiator of cytokinesis without apparent involvement in mitosis in the trypanosome, was either depleted or overexpressed in the TbAUK1-deficient cells. A dominant TbAUK1-depleted phenotype was demonstrated in both cases, suggesting that TbAUK1 plays an essential role in cytokinesis that cannot be affected by changes in the level of T. brucei polo-like kinase. To our knowledge, this is the first time that the function of an aurora B-like kinase is a prerequisite for polo-like kinase action in initiating cytokinesis. TbAUK1 is also the first identified protein that couples both mitosis and kinetoplast replication with cytokinesis in the trypanosome.