Plk4 Phosphorylates Ana2 to Trigger Sas6 Recruitment and Procentriole Formation

Centrioles are 9-fold symmetrical structures at the core of centrosomes and base of cilia whose dysfunction has been linked to a wide range of inherited diseases and cancer [1]. Their duplication is regulated by a protein kinase of conserved structure, the C. elegans ZYG-1 or its Polo-like kinase 4 (Plk4) counterpart in other organisms [2–4]. Although Plk4’s centriolar partners and mechanisms that regulate its stability are known, its crucial substrates for centriole duplication have never been identified. Here we show that Drosophila Plk4 phosphorylates four conserved serines in the STAN motif of the core centriole protein Ana2 to enable it to bind and recruit its Sas6 partner. Ana2 and Sas6 normally load onto both mother and daughter centrioles immediately after their disengagement toward the end of mitosis to seed procentriole formation. Nonphosphorylatable Ana2 still localizes to the centriole but can no longer recruit Sas6 and centriole duplication fails. Thus, following centriole disengagement, recruitment of Ana2 and its phosphorylation by Plk4 are the earliest known events in centriole duplication to recruit Sas6 and thereby establish the architecture of the new procentriole engaged with its parent. •Plk4 phosphorylates Ana2 at essential residues in its conserved STAN motif•Plk4 phosphorylation triggers the direct interaction of Ana2 with Sas6•Ana2 phosphorylated by Plk4 recruits Sas6 to centrioles at the end of mitosis•A phospho-null Ana2 mutant fails to recruit Sas6 and duplicate centrioles Plk4 kinase triggers centriole duplication. However, its critical substrate has never been found. Here we show that Drosophila Plk4 phosphorylates four conserved serines in the STAN motif of the core centriole protein Ana2. This enables Ana2 to bind and recruit Sas6 toward the end of mitosis to trigger procentriole formation in the next cell cycle.