Different Drosophila cell types exhibit differences in mitotic centrosome assembly dynamics

Centrosomes are major microtubule organising centres comprising a pair of centrioles surrounded by pericentriolar material (PCM). The PCM expands dramatically as cells enter mitosis, and we previously showed that two key PCM components, Centrosomin (Cnn) and Spd-2, cooperate to form a scaffold structure around the centrioles that recruits the mitotic PCM in Drosophila; the SPD-5 and SPD-2 proteins appear to play a similar function in C. elegans[1–3]. In fly syncytial embryos, Cnn and Spd-2 are initially recruited into a central region of the PCM and then flux outwards [4–6]. This centrosomal flux is potentially important, but it has so far not been reported in any other cell type. Here we examine the dynamic behaviour of Cnn and Spd-2 in Drosophila larval brain cells. Spd-2 fluxes outwards from the centrioles in both brains and embryos in a microtubule-independent manner. In contrast, although Cnn is initially incorporated into the region of the PCM occupied by Spd-2 in both brains and embryos, Cnn fluxes outwards along microtubules in embryos, but not in brain cells, where it remains concentrated around the centrosomal Spd-2. Thus, the microtubule-independent centrosomal-flux of Spd-2 occurs in multiple fly cell types, while the microtubule-dependent outward flux of Cnn appears to be restricted to the syncytial embryo.