Sas-4 provides a scaffold for cytoplasmic complexes and tethers them in a centrosome

Abstract

Centrosomes are conserved organelles that are essential for accurate cell division and cilium formation. A centrosome consists of a pair of centrioles surrounded by a protein network of pericentriolar material (PCM) that is essential for the centrosome’s function. In this study, we show that Sas-4 provides a scaffold for cytoplasmic complexes (named S-CAP), which include CNN, Asl and D-PLP, proteins that are all found in the centrosomes at the vicinity of the centriole. When Sas-4 is absent, nascent procentrioles are unstable and lack PCM, and functional centrosomes are not generated. When Sas-4 is mutated, so that it cannot form S-CAP complexes, centrosomes are present but with dramatically reduced levels of PCM. Finally, purified S-CAP complexes or recombinant Sas-4 can bind centrosomes stripped of PCM, whereas recombinant CNN or Asl cannot. In summary, PCM assembly begins in the cytosol where Sas-4 provides a scaffold for pre-assembled cytoplasmic complexes before tethering of the complexes in a centrosome.

CPAP promotes timely cilium disassembly to maintain neural progenitor pool

“…However, the mechanisms involved in NPCs maintenance still remain unclear. The finding that several known microcephaly proteins are found in centrosomes suggested that a centrosomal mechanism can control neuronal number in a developing brain (Bond et al , 2005, 2005; Basto et al , 2006; Thornton & Woods, 2009, 2009; Gopalakrishnan et al , 2011; Hussain et al , 2012). Centrosomes are the major microtubule‐organizing centers of animal cells.…”

The Centrosome and Its Duplication Cycle

“…When expressed in Drosophila embryos, either Sas-4 alone or a mutant form of Asl able to bind Sas-4 but not Plk4 can promote formation of acentriolar PCM aggregates that nucleate cytoplasmic microtubules (Dzhindzhev et al 2010). Moreover, Sas-4 null mutant flies show a reduction of PCM components in testes (Gopalakrishnan et al 2011(Gopalakrishnan et al , 2012. This reflects the ability of Sas-4 to form complexes with CNN and Dplp; centrosomes with mutant Sas-4 unable to form such complexes have reduced PCM (Dzhindzhev et al 2010;Gopalakrishnan et al 2011).…”

“…Moreover, Sas-4 null mutant flies show a reduction of PCM components in testes (Gopalakrishnan et al 2011(Gopalakrishnan et al , 2012. This reflects the ability of Sas-4 to form complexes with CNN and Dplp; centrosomes with mutant Sas-4 unable to form such complexes have reduced PCM (Dzhindzhev et al 2010;Gopalakrishnan et al 2011). A double mutation in Sas-4 protein se-quence that abolishes its binding to tubulin enhances centrosomal protein complex formation leading to abnormally large centrosomes and asters (Gopalakrishnan et al 2012).…”

Acentriolar mitosis activates a p53-dependent apoptosis pathway in the mouse embryo

“…Spindle assembly defective-4 (SAS4), one of these core proteins, acts at an early step in the assembly pathway, when it is required for the addition of tubulin subunits to the forming procentrioles; it also is required for recruitment of the pericentriolar material (PCM) to form the centrosome (3,20,21). Mutations in Sas4 block centriole formation in Drosophila and C. elegans, and mutations in human SAS4 (CPAP/CENPJ) cause Seckel syndrome (dwarfism with microcephaly) (3)(4)(5)(6).…”