Structure-Specific Endonucleases and the Resolution of Chromosome Underreplication

Abstract

Complete genome duplication in every cell cycle is fundamental for genome stability and cell survival. However, chromosome replication is frequently challenged by obstacles that impede DNA replication fork (RF) progression, which subsequently causes replication stress (RS). Cells have evolved pathways of RF protection and restart that mitigate the consequences of RS and promote the completion of DNA synthesis prior to mitotic chromosome segregation. If there is entry into mitosis with underreplicated chromosomes, this results in sister-chromatid entanglements, chromosome breakage and rearrangements and aneuploidy in daughter cells. Here, we focus on the resolution of persistent replication intermediates by the structure-specific endonucleases (SSEs) MUS81, SLX1-SLX4 and GEN1. Their actions and a recently discovered pathway of mitotic DNA repair synthesis have emerged as important facilitators of replication completion and sister chromatid detachment in mitosis. As RS is induced by oncogene activation and is a common feature of cancer cells, any advances in our understanding of the molecular mechanisms related to chromosome underreplication have important biomedical implications.

Topoisomerase II deficiency leads to a postreplicative structural shift in all Saccharomyces cerevisiae chromosomes

“…By contrast, chromosomes other than XII manifest the same PFGE behaviour much later in the cell cycle; after replication appears to have ended by both FACS and PFGE (Figures 1, 2, 4, 5, S1, S3-S7). A closer look at this late PFGE behaviour suggests it is independent of transition between cell cycle stages (i.e., Sphase to metaphase to anaphase) and the key spatial and molecular changes that occur in such transitions (e.g., activation of structure-specific endonucleases, spindle pulling forces, hypercondensation by Cdc14, etc) [2,49] (Figure 7a), which are particularly enriched when cells cannot sense RF problems [56]. This scenario is compatible with the presence of Rad52independent NN-2D X-shaped signals (Figure 4).…”

Working on Genomic Stability: From the S-Phase to Mitosis

“…It has been shown that the cell cycle machinery itself regulates MiDAS. Accordingly, Cdk1 kinase, the major regulator of mitosis, phosphorylates EME1 and SLX4 at the onset of mitosis to promote their interaction to form an SLX-MUS complex (SLX1-SLX4-MUS81-EME1) [82,187] (Table 1). This mechanism is similar to the one described for budding yeast, in which the orthologues Mus81-Mms4 are hyperactivated at the G2/M transition by Cdc28/Cdk1 and Cdc5 (polo-like kinase 1 or Plk1 in vertebrates) [81,188].…”

Chromothripsis and DNA Repair Disorders

“…Replication stress may have a dual role of initiating micronuclei formation and promoting DSBs within the micronucleus once it has been formed. The delayed/stalled replication observed in micronuclei may cause a large number of unresolved replication intermediates, which are known to trigger endonuclease-dependent DSB formation [14]; and upon mitotic entry (following disruption of the micronuclear/nuclear membranes), the DNA damage response pathway will then promote the repair of the massive DSBs, leading to chromothripsis.…”