Cdk1 Phosphorylates Drosophila Sas-4 to Recruit Polo to Daughter Centrioles and Convert Them to Centrosomes

Abstract

SummaryCentrosomes and cilia are organized by a centriole pair comprising an older mother and a younger daughter. Centriole numbers are tightly regulated, and daughter centrioles (which assemble in S phase) cannot themselves duplicate or organize centrosomes until they have passed through mitosis. It is unclear how this mitotic “centriole conversion” is regulated, but it requires Plk1/Polo kinase. Here we show that in flies, Cdk1 phosphorylates the conserved centriole protein Sas-4 during mitosis. This creates a Polo-docking site that helps recruit Polo to daughter centrioles and is required for the subsequent recruitment of Asterless (Asl), a protein essential for centriole duplication and mitotic centrosome assembly. Point mutations in Sas-4 that prevent Cdk1 phosphorylation or Polo docking do not block centriole disengagement during mitosis, but block efficient centriole conversion and lead to embryonic lethality. These observations can explain why daughter centrioles have to pass through mitosis before they can duplicate and organize a centrosome.

Once and only once: mechanisms of centriole duplication and their deregulation in disease

“…For procentrioles, competence for duplication additionally requires the acquisition of PCM, a process termed ‘centriole to centrosome conversion’ 89,90 , which is also governed by CDK1 and PLK1 91,92 (Figure 2A). Best described are events in Drosophila , where PLK1 is first recruited to CPAP, through CDK1-dependent phosphorylation of a single docking site 92 .…”

“…Best described are events in Drosophila , where PLK1 is first recruited to CPAP, through CDK1-dependent phosphorylation of a single docking site 92 . In both Drosophila and mammalian cells, PLK1 then triggers the sequential assembly of CEP135, CEP295/Ana1 and CEP152/Asl and downstream PCM formation 58,89,90 .…”

Albatross/FBF1 contributes to both centriole duplication and centrosome separation

“…Plk1 also phosphorylates Cnn (the Drosophila melanogaster homologue of mammalian CDK5RAP2) (Conduit et al, 2014) and pericentrin (Lee & Rhee, 2011) during centrosome maturation. In the fruit fly, Cdk1 phosphorylates Sas-4 (the CPAP homologue), recruits Polo to daughter centrioles, and converts them to centrosomes (PCM-assembly and duplication competent) (Novak, Wainman, Gartenmann, & Raff, 2016). Although how these enzymatic events occur at the proximal ends of centrioles is less understood, proteins harboring the Cdk1-dependent priming phosphorylation site may bind to the Polo-box domain (PBD) in Plk1 (Elia, Cantley, & Yaffe, 2003;Zitouni et al, 2014).…”

Dynamic centriolar relocalization of Polo kinase and Centrobin in early mitosis primes centrosome asymmetry in fly neural stem cells

“…Consistent with previous reports 1,24-26 we found that Sas-6 was localized to the centriolar cartwheel whereas Asterless (Asl) surrounded the centriolar wall (Supplementary Fig.1d). Asl has been shown to extend from the core centriolar region into the adjacent PCM and sequentially loads onto the new centriole during centriole-to-centrosome conversion (also referred to as mitotic centriole conversion), a mechanism generating a centriole-duplication and PCM-assembly competent centrosome 25,27,28 . Apical and basal interphase neuroblast centrosomes contained two Sas-6 + cartwheels but only one Asl + centriole (Supplementary Fig.1d, yellow arrowhead).…”