Sas- 6/Ana2 Particles (SAPs) as a new model to probe the pathway of centriole and centrosome assembly

Centriole assembly requires a small number of conserved proteins. The precise pathway of centriole assembly has been difficult to study, as the lack of any one of the core assembly proteins—Plk4, Ana2/STIL, Sas-6, Sas- 4/CPAP or Asl/Cep152—leads to the absence of centrioles. Here we use Sas- 6/Ana2 Particles (SAPs) as a new model to probe the pathway of centriole and centrosome assembly. SAPs form in Drosophila eggs/embryos when Sas-6 and Ana2 are overexpressed. SAP assembly requires Sas-4, but not Plk4, while Asl helps to initiate SAP assembly, but is not required for SAP growth. Although not centrioles, SAPs recruit and organize many centriole and centrosome components, nucleate microtubules, organise actin structures and compete with endogenous centrosomes to form mitotic spindle poles. SAPs require Asl/Cep152 to efficiently recruit pericentriolar material (PCM), but Spd-2/Cep192 can promote some PCM assembly independently of Asl/Cep152. These observations provide new insights into the pathways of centriole and centrosome assembly.