Repo-Man Coordinates Chromosomal Reorganization with Nuclear Envelope Reassembly during Mitotic Exit

Abstract

SummaryRepo-Man targets protein phosphatase 1 γ (PP1γ) to chromatin at anaphase onset and regulates chromosome structure during mitotic exit. Here, we show that a Repo-Man:PP1 complex forms in anaphase following dephosphorylation of Repo-Man. Upon activation, the complex localizes to chromosomes and causes the dephosphorylation of histone H3 (Thr3, Ser10, and Ser28). In anaphase, Repo-Man has both catalytic and structural functions that are mediated by two separate domains. A C-terminal domain localizes Repo-Man to bulk chromatin in early anaphase. There, it targets PP1 for the dephosphorylation of histone H3 and possibly other chromosomal substrates. An N-terminal domain localizes Repo-Man to the chromosome periphery later in anaphase. There, it is responsible for the recruitment of nuclear components such as Importin β and Nup153 in a PP1-independent manner. These observations identify Repo-Man as a key factor that coordinates chromatin remodeling and early events of nuclear envelope reformation during mitotic exit.

Ki67 Antigen Contributes to the Timely Accumulation of Protein Phosphatase 1γ on Anaphase Chromosomes

“…1A), suggesting that the interaction of these two proteins with PP1␥ might be regulated by similar mechanisms. As for the interaction of Repo-MAN with PP1␥, this interaction was shown to be negatively regulated by phosphorylation at Thr-412, a threonine residue that is 17 amino acids downstream of the PP1-binding motif (32) and corresponds to Thr-165 in human Ki67 (Fig. 1A).…”

“…RNAi-The sequences for siRNAs used were as follows: siGL2, 5Ј-CGUACGCGGAAUACUUCGA-3Ј; si31 (Ki67), 5Ј-GGAAGGUCUACAGAGUUCAGGAAUA-3Ј; si32 (Ki67), 5Ј-UCUGGAAGACCUGACUGGCUUUAAA-3Ј; siRepo-MAN, 5Ј-UGACAGACUUGACCAGAAATT-3Ј (32). siRNA transfections were performed using Lipofectamine RNAiMAX (Invitrogen) according to the manufacturer's instructions.…”

The Mitotic Protein Kinase Haspin and Its Inhibitors

“…The H3T3ph-dephosphorylating enzyme has been shown to be the PP1γ phosphatase specifically targeted to anaphase chromosomes by its regulatory subunit Repo-Man [37,38]. Further studies showed that Repo-Man targeting to chromosomes is negatively regulated through Aurora B phosphorylation explaining the persistent H3T3ph signal observed on telomeres at anaphase [37].…”

The Biochemistry of Mitosis

“…In budding yeast, Cdc14 is important and is activated when the cyclin-Cdk1 levels drop below a threshold that allows Cdc14 to be released from a nuclear inhibitor by a pathway that also requires separase (reviewed in Stegmeier and Amon 2004;Rock and Amon 2009). In most other systems, the PP1 and PP2A complexes are most clearly implicated in controlling anaphase and mitotic exit (Kinoshita et al 1990;Vagnarelli et al 2011;Wurzenberger et al 2012).…”

“…PP1 is targeted to a number of structures in anaphase to help to reshape the subcellular architecture during mitotic exit. For example, Repo-Man protein targets PP1 to chromosomes in anaphase to coordinate chromosome decondensation (Vagnarelli et al 2011), and the AKAP149 protein targets PP1 to the nuclear envelope to allow nuclear lamin reassembly (Steen et al 2000). The drop in cyclin -Cdk activity levels in anaphase indirectly reactivates PP2A complexes because Greatwall kinase depends on cyclin -Cdk for its activity.…”