A model of how Akt contributes to centrosome separation in the syncytial blastoderm. (A) In wild-type embryos, cortical Akt phosphorylates Zw3, ensuring it remains inactive. A complex of Arm and APC2 is able to interact with the actin cortex and with the MT + Tip protein EB1. The stable interaction between the cortex and MTs allows cortical dynein to generate the force required for full centrosome separation. (B) In embryos in which akt levels are severely reduced, Zw3 is no longer phosphorylated. The active Zw3 kinase can now phosphorylate both APC2 and Arm. Phosphorylated Arm is targeted for degradation, disrupting the cortical complex. EB1, although able to bind MTs, cannot stably associate with the actin cortex in the absence of cortical Arm–APC2. Cortical dynein is able to transiently interact with MTs and generate force. However, the force required for full centrosome separation is now greater than can be generated in the absence of Arm–APC2. Consequently, centrosome separation stops before completion.