In collaboration with the Peifer lab, we are using Drosophila as a model system to study the biology of the centrosome. We recently discovered that, although fly cells use centrosomes to organize their mitotic spindle poles, centrosomes are inactivated and disassembled at the conclusion of mitosis. As a result, many cell types do not possess an interphase centrosome microtubule organizing center in flies. An ongoing project aims to elucidate the molecular basis for this dramatic cycle of centrosome maturation and disassembly.
We are also using the system and tools we have generated to study how centrosome duplication is regulated. In most normal cells, centrosome duplication is regulated by a "block" that prevents duplication events from occurring more than once per cell cycle. Interestingly, this duplication block is absent from many types of transformed cells. Previous work had implicated ubiquitin-mediated protein degradation as a key component of this block because mutations in the SCF ubiquitin ligase complex give rise to centrosome overduplication in mice and in flies. We conducted a genome-wide screen to identify the SCF components involved in regulating centriole numbers in fly cells and leveraged this information to identify its target as polo-like kinase 4 (Plk4). Our model is that Plk4 acts to initiate centriole duplication via its kinase activity by phosphorylating a protein associated with the mother centriole during mitosis/early G1 phase of the cell cycle. The SCF complex then targets Plk4 for ubiquitination and proteolysis at the centriole, thus suppressing its activity and limiting the initiation of centriole duplication to once per cell cycle. Future work will identify additional components of this important regulatory circuit and identify Plk4 targets involved in centriole biogenesis.
