Figure 7. A schematic model of how the D-TACC–Msps complex stabilizes MTs in D. melanogaster embryos. MTs are nucleated at centrosomes by the -tubulin ring complex (-TuRC). These MTs are often released from -TuRC but are held in the vicinity of the centrosome by the action of MT motors. The bulk of D-TACC–Msps complexes (that are present at centrosomes, along MTs, and throughout the cytoplasm) can bind these MTs either laterally or at plus ends and stabilize them (mechanism 1). Aurora A can specifically activate a small fraction of D-TACC–Msps complexes that are at the centrosome. This allows the phosphorylated complexes (P, red) to interact with and stabilize MT minus ends (mechanism 2). Importantly, this mechanism is only active at centrosomes, and any MTs that form in the cytoplasm will not be stabilized in this way. This may explain, at least in part, why centrosomes are such dominant sites of MT assembly in mitosis.