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

Zsofia A Novak,Alan Wainman,Lisa Gartenmann,Jordan W Raff

doi:10.1016/j.devcel.2016.05.022

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.

Highlights

This configuration appears to be crucial for regulating centriole numbers, as mother centrioles normally cannot duplicate again until they disengage from their daughters during the subsequent mitosis, a process that requires the mitotic kinase Polo/Plk1 (Loncarek et al, 2010; Shukla et al, 2015; Tsou and Stearns, 2006a; Tsou et al, 2009)
It was recently shown that newborn daughter centrioles cannot form centrosomes or duplicate until they have passed through mitosis and are modified by Polo/Plk1 (Wang et al, 2011); this process has been termed ‘‘centriole-to-centrosome’’ conversion (Fu et al, 2016; Izquierdo et al, 2014; Wang et al, 2011), we sometimes use the more generic ‘‘mitotic centriole conversion’’ here
Sas-4 Thr200 Is Required to Recruit Asl to New Centrioles To investigate whether the ability of Sas-4 to recruit Asl to centrioles might be regulated by cell-cycle-dependent phosphorylation we searched for regions within, or adjacent to, the Asl-interacting region of Sas-4 (Dzhindzhev et al, 2010) that contained consensus phosphorylation sites for either Cyclin-dependent kinases (Cdks) or Polo/Plk kinases and that were conserved in Drosophila species

Summary

Introduction

Most cells are born with two centrioles that are precisely duplicated in S phase when a new ‘‘daughter’’ centriole is assembled at right angles to each ‘‘mother’’ in a tightly apposed engaged configuration. This configuration appears to be crucial for regulating centriole numbers, as mother centrioles normally cannot duplicate again until they disengage from their daughters during the subsequent mitosis, a process that requires the mitotic kinase Polo/Plk (Loncarek et al, 2010; Shukla et al, 2015; Tsou and Stearns, 2006a; Tsou et al, 2009). Mother centrioles normally only duplicate once in S phase, and disengagement functions as a ‘‘license’’ that is acquired during mitosis to enable mother centrioles to duplicate again during the S phase (Fırat-Karalar and Stearns, 2014; Nigg, 2007; Tsou and Stearns, 2006b)

Results

Discussion

Conclusion