Histone Chaperone NAP1 Mediates Sister Chromatid Resolution by Counteracting Protein Phosphatase 2A

Abstract

Chromosome duplication and transmission into daughter cells requires the precisely orchestrated binding and release of cohesin. We found that the Drosophila histone chaperone NAP1 is required for cohesin release and sister chromatid resolution during mitosis. Genome-wide surveys revealed that NAP1 and cohesin co-localize at multiple genomic loci. Proteomic and biochemical analysis established that NAP1 associates with the full cohesin complex, but it also forms a separate complex with the cohesin subunit stromalin (SA). NAP1 binding to cohesin is cell-cycle regulated and increases during G2/M phase. This causes the dissociation of protein phosphatase 2A (PP2A) from cohesin, increased phosphorylation of SA and cohesin removal in early mitosis. PP2A depletion led to a loss of centromeric cohesion. The distinct mitotic phenotypes caused by the loss of either PP2A or NAP1, were both rescued by their concomitant depletion. We conclude that the balanced antagonism between NAP1 and PP2A controls cohesin dissociation during mitosis.

Phospho-H1 Decorates the Inter-chromatid Axis and Is Evicted along with Shugoshin by SET during Mitosis

“…The complex of SET-SGOL2 was resistant to salt washes up to 400 mM NaCl, highlighting that their interaction was strong and specific (Figure 1F). The related chaperone NAP1 did not associate with SGOL2 (Figure S1H), consistent with a previous study in Drosophila showing that NAP1 did not interact with the Shugoshin homolog, MEIS322 (Moshkin et al, 2013). Impairment of the SET dimerization domain (DIM mutant), but not its acidic C-terminal domain (ACID mutant, which can still form a dimer) completely abolished SGOL2 binding, showing that SET dimerization is necessary and sufficient for SGOL2 binding in vitro (Figure 1F, Figure S1F).…”

MGO3 and GIP1 act synergistically for the maintenance of centromeric cohesion

“…8 In animals, a dual role was described for the histone chaperone nucleosome assembly protein 1 (NAP1) controlling sister chromatid separation independently of its function in nucleosome assembly. 24 It is worth noting that human TONSL was shown to be an H3-1/ H4 chaperone needed for nucleosome assembly after the restart of stalled replication forks, 25 but its role in the control of centromeric replication has not been investigated so far.…”

Nucleosome Assembly Proteins Get SET to Defeat the Guardian of Chromosome Cohesion

“…Do the related Nap1 proteins play similar roles? The new study in this issue [3] expands on these points.…”

“…In meiosis, cohesion between chromosome arms facilitates segregation of recombined homologues during meiosis I by stabilizing the physical linkages (chiasmata) between them, and cohesion between centromeres is essential for accurate segregation of sisters in meiosis II [1], [2]. A study by Moshkin and colleagues in this issue of PLOS Genetics [3] sheds new light on how these processes are regulated.…”

“…(A) In mitosis, cohesin (red rings) is phosphorylated and removed from chromosome arms by the “prophase pathway.” In this issue, Moshkin et al provide evidence that Nap1 (blue) can displace PP2A (green) from cohesin to further promote cohesin release from chromosomes [3]. Cohesin at centromeres is protected by shugoshin-PP2A (yellow) until the metaphase–anaphase transition, when tension across bi-oriented sister kinetochores leads to the movement of shugoshin-PP2A away from cohesin at inner centromeres, allowing cohesin to be cleaved by separase [6].…”