Drosophila Ajuba is not an Aurora-A activator but is required to maintain Aurora-A at the centrosome.

The LIM-domain protein Ajuba localizes at sites of epithelial cell-cell adhesion and has also been implicated in the activation of Aurora-A (Aur-A). Despite the expected importance of Ajuba, Ajuba-deficient mice are viable, which has been attributed to functional redundancy with the related LIM-domain protein LIMD1. To gain insights into the function of Ajuba, we investigated its role in Drosophila, where a single gene (jub) encodes a protein closely related to Ajuba and LIMD1. We identified a key function in neural stem cells, where Jub localizes to the centrosome. In these cells, mutation in jub leads to centrosome separation defects and aberrant mitotic spindles, which is a phenotype similar to that of aur-A mutants. We show that in jub mutants Aur-A activity is not perturbed, but that Aur-A recruitment and maintenance at the centrosome is affected. As a consequence the active kinase is displaced from the centrosome. On the basis of our studies in Drosophila neuroblasts, we propose that a key function of Ajuba, in these cells, is to maintain active Aur-A at the centrosome during mitosis.