An Alternatively Spliced Bifunctional Localization Signal Reprograms Human Shugoshin 1 to Protect Centrosomal Instead of Centromeric Cohesin

Separation of human sister chromatids involves the removal of DNA embracing cohesin ring complexes. Ring opening occurs by prophase-pathway-dependent phosphorylation and separase-mediated cleavage, with the former being antagonized at centromeres by Sgo1-dependent PP2A recruitment. Intriguingly, prophase pathway signaling and separase's proteolytic activity also bring about centriole disengagement, whereas Sgo1 is again counteracting this licensing step of later centrosome duplication. Here, we demonstrate that alternative splice variants of human Sgo1 specifically and exclusively localize and function either at centromeres or centrosomes. A small C-terminal peptide encoded by exon 9 of SGO1 (CTS for centrosomal targeting signal of human Sgo1) is necessary and sufficient to drive centrosomal localization and simultaneously abrogate centromeric association of corresponding Sgo1 isoforms. Cohesin is shown to be a target of the prophase pathway at centrosomes and protected by Sgo1-PP2A. Accordingly, premature centriole disengagement in response to Sgo1 depletion is suppressed by blocking ring opening of an engineered cohesin.