Drosophila APC2 and Armadillo participate in tethering mitotic spindles tocortical actin

Proper positioning of mitotic spindles ensures equal allocation of chromoso mes to daughter cells. This often involves interactions between spindle and astral microtubules and cortical actin(1). In yeast and Caenorhabditis ele gans, some of the protein machinery that connects spindles and cortex has b een identified but, in most animal cells, this process remains mysterious. Here, we report that the tumour suppresser homologue APC2 and its binding p artner Armadillo both play roles in spindle anchoring during the syncytial mitoses of early Drosophila embryos. Armadillo, alpha -catenin and APC2 all localize to sites of cortical spindle attachment. APC2-Armadillo complexes often localize with interphase microtubules. Zeste-white 3 kinase, which c an phosphorylate Armadillo and APC, is also crucial for spindle positioning and regulates the localization of APC2-Armadillo complexes. Together, thes e data suggest that APC2, Armadillo and alpha -catenin provide an important link between spindles and cortical actin, and that this link is regulated by Zeste-white 3 kinase.