Imaging Centrosomes in Fly Testes

Centrosomes are conserved microtubule-based organelles whose structure and function change dramatically throughout the cell cycle and cell ...

Regulated centrosome biogenesis is required for accurate cell division and for maintaining genome integrity. Centrosomes consist of a centriole pair surrounded by a protein network known as pericentriolar material (PCM). PCM assembly is a tightly regulated, critical step that determines the size and capability of centrosomes. Here, we report a role for tubulin in regulating PCM recruitment through the conserved centrosomal protein Sas-4. Tubulin directly binds to Sas-4; together they are components of cytoplasmic complexes of centrosomal proteins. A Sas-4 mutant, which cannot bind tubulin, enhances centrosomal protein complex formation and has abnormally large centrosomes with excessive activity. These results suggest that tubulin negatively regulates PCM recruitment. Whereas tubulin-GTP prevents Sas-4 from forming protein complexes, tubulin-GDP promotes it. Thus, the regulation of PCM recruitment by tubulin depends on its GTP/GDP-bound state. These results identify a role for tubulin in regulating PCM recruitment independent of its well-known role as a building block of microtubules. On the basis of its guanine-bound state, tubulin can act as a molecular switch in PCM recruitment.

Marcus L. Basiri

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