1
|
Yang R, Hunker O, Wise M, Bleichert F. Multiple pathways for licensing human replication origins. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.10.588796. [PMID: 38645015 PMCID: PMC11030351 DOI: 10.1101/2024.04.10.588796] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
The loading of replicative helicases constitutes an obligatory step in the assembly of DNA replication machineries. In eukaryotes, the MCM2-7 replicative helicase motor is deposited onto DNA by the origin recognition complex (ORC) and co-loader proteins as a head-to-head MCM double hexamer to license replication origins. Although extensively studied in the budding yeast model system, the mechanisms of origin licensing in higher eukaryotes remain poorly defined. Here, we use biochemical reconstitution and electron microscopy (EM) to reconstruct the human MCM loading pathway. Unexpectedly, we find that, unlike in yeast, ORC's Orc6 subunit is not essential for human MCM loading but can enhance loading efficiency. EM analyses identify several intermediates en route to MCM double hexamer formation in the presence and absence of Orc6, including an abundant DNA-loaded, closed-ring single MCM hexamer intermediate that can mature into a head-to-head double hexamer through different pathways. In an Orc6-facilitated pathway, ORC and a second MCM2-7 hexamer are recruited to the dimerization interface of the first hexamer through an MCM-ORC intermediate that is architecturally distinct from an analogous intermediate in yeast. In an alternative, Orc6-independent pathway, MCM double hexamer formation proceeds through dimerization of two independently loaded single MCM2-7 hexamers, promoted by a propensity of human MCM2-7 hexamers to dimerize without the help of other loading factors. This redundancy in human MCM loading pathways likely provides resilience against replication stress under cellular conditions by ensuring that enough origins are licensed for efficient DNA replication. Additionally, the biochemical reconstitution of human origin licensing paves the way to address many outstanding questions regarding DNA replication initiation and replication-coupled events in higher eukaryotes in the future.
Collapse
Affiliation(s)
| | | | - Marleigh Wise
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA
| | - Franziska Bleichert
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA
| |
Collapse
|
2
|
Schoch K, Ruegg MSG, Fellows BJ, Cao J, Uhrig S, Einsele-Scholz S, Biskup S, Hawarden SRA, Salpietro V, Capra V, Brown CM, Accogli A, Shashi V, Bicknell LS. A second hotspot for pathogenic exon-skipping variants in CDC45. Eur J Hum Genet 2024:10.1038/s41431-024-01583-1. [PMID: 38467731 DOI: 10.1038/s41431-024-01583-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2023] [Revised: 02/13/2024] [Accepted: 02/26/2024] [Indexed: 03/13/2024] Open
Abstract
Biallelic pathogenic variants in CDC45 are associated with Meier-Gorlin syndrome with craniosynostosis (MGORS type 7), which also includes short stature and absent/hypoplastic patellae. Identified variants act through a hypomorphic loss of function mechanism, to reduce CDC45 activity and impact DNA replication initiation. In addition to missense and premature termination variants, several pathogenic synonymous variants have been identified, most of which cause increased exon skipping of exon 4, which encodes an essential part of the RecJ-orthologue's DHH domain. Here we have identified a second cohort of families segregating CDC45 variants, where patients have craniosynostosis and a reduction in height, alongside common facial dysmorphisms, including thin eyebrows, consistent with MGORS7. Skipping of exon 15 is a consequence of two different variants, including a shared synonymous variant that is enriched in individuals of East Asian ancestry, while other variants in trans are predicted to alter key intramolecular interactions in α/β domain II, or cause retention of an intron within the 3'UTR. Our cohort and functional data confirm exon skipping is a relatively common pathogenic mechanism in CDC45, and highlights the need for alternative splicing events, such as exon skipping, to be especially considered for variants initially predicted to be less likely to cause the phenotype, particularly synonymous variants.
Collapse
Affiliation(s)
- Kelly Schoch
- Division of Medical Genetics, Department of Pediatrics, Duke University School of Medicine, Durham, NC, USA
| | - Mischa S G Ruegg
- Department of Biochemistry, University of Otago, Dunedin, New Zealand
| | - Bridget J Fellows
- Department of Biochemistry, University of Otago, Dunedin, New Zealand
| | - Joseph Cao
- Division of Pediatric Radiology, Department of Radiology Duke University School of Medicine, Durham, NC, USA
| | - Sabine Uhrig
- Institute of Clinical Genetics, Klinikum Stuttgart, Stuttgart, Germany
| | | | - Saskia Biskup
- Center for Human Genetics Tuebingen and CeGaT GmbH, Tuebingen, Germany
| | - Samuel R A Hawarden
- Department of Pathology, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
| | - Vincenzo Salpietro
- Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, L'Aquila, Italy
| | - Valeria Capra
- Genomics and Clinical Genetics, IRCCS Istituto Giannina Gaslini, Genoa, Italy
| | - Chris M Brown
- Department of Biochemistry, University of Otago, Dunedin, New Zealand
| | - Andrea Accogli
- Department of Specialized Medicine, Division of Medical Genetics, McGill University Health Centre, Montreal, QC, Canada
- Department of Human Genetics, Faculty of Medicine, McGill University, Montreal, QC, Canada
| | - Vandana Shashi
- Division of Medical Genetics, Department of Pediatrics, Duke University School of Medicine, Durham, NC, USA
| | - Louise S Bicknell
- Department of Biochemistry, University of Otago, Dunedin, New Zealand.
| |
Collapse
|
3
|
Stewart GS. DONSON: Slding in 2 the limelight. DNA Repair (Amst) 2024; 134:103616. [PMID: 38159447 DOI: 10.1016/j.dnarep.2023.103616] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Revised: 11/18/2023] [Accepted: 12/19/2023] [Indexed: 01/03/2024]
Abstract
For over a decade, it has been known that yeast Sld2, Dpb11, GINS and Polε form the pre-loading complex (pre-LC), which is recruited to a CDC45-bound MCM2-7 complex by the Sld3/Sld7 heterodimer in a phospho-dependent manner. Whilst functional orthologs of Dbp11 (TOPBP1), Sld3 (TICRR) and Sld7 (MTBP) have been identified in metazoans, controversy has surrounded the identity of the Sld2 ortholog. It was originally proposed that the RECQ helicase, RECQL4, which is mutated in Rothmund-Thomson syndrome, represented the closest vertebrate ortholog of Sld2 due to a small region of sequence homology at its N-Terminus. However, there is no clear evidence that RECQL4 is required for CMG loading. Recently, new findings suggest that the functional ortholog of Sld2 is actually DONSON, a replication fork stability factor mutated in a range of neurodevelopmental disorders characterised by microcephaly, short stature and limb abnormalities. These studies show that DONSON forms a complex with TOPBP1, GINS and Polε analogous to the pre-LC in yeast, which is required to position the GINS complex on the MCM complex and initiate DNA replication. Taken together with previously published functions for DONSON, these observations indicate that DONSON plays two roles in regulating DNA replication, one in promoting replication initiation and one in stabilising the fork during elongation. Combined, these findings may help to uncover why DONSON mutations are associated with such a wide range of clinical deficits.
Collapse
Affiliation(s)
- Grant S Stewart
- Institute of Cancer and Genomic Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
| |
Collapse
|
4
|
Evrin C, Alvarez V, Ainsworth J, Fujisawa R, Alabert C, Labib KPM. DONSON is required for CMG helicase assembly in the mammalian cell cycle. EMBO Rep 2023; 24:e57677. [PMID: 37781960 PMCID: PMC10626419 DOI: 10.15252/embr.202357677] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Revised: 09/15/2023] [Accepted: 09/19/2023] [Indexed: 10/03/2023] Open
Abstract
DONSON is one of 13 genes mutated in a form of primordial microcephalic dwarfism known as Meier-Gorlin syndrome. The other 12 encode components of the CDC45-MCM-GINS helicase, around which the eukaryotic replisome forms, or are factors required for helicase assembly during DNA replication initiation. A role for DONSON in CDC45-MCM-GINS assembly was unanticipated, since DNA replication initiation can be reconstituted in vitro with purified proteins from budding yeast, which lacks DONSON. Using mouse embryonic stem cells as a model for the mammalian helicase, we show that DONSON binds directly but transiently to CDC45-MCM-GINS during S-phase and is essential for chromosome duplication. Rapid depletion of DONSON leads to the disappearance of the CDC45-MCM-GINS helicase from S-phase cells and our data indicate that DONSON is dispensable for loading of the MCM2-7 helicase core onto chromatin during G1-phase, but instead is essential for CDC45-MCM-GINS assembly during S-phase. These data identify DONSON as a missing link in our understanding of mammalian chromosome duplication and provide a molecular explanation for why mutations in human DONSON are associated with Meier-Gorlin syndrome.
Collapse
Affiliation(s)
- Cecile Evrin
- The MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life SciencesUniversity of DundeeDundeeUK
| | - Vanesa Alvarez
- Division of Molecular, Cell & Developmental Biology, School of Life SciencesUniversity of DundeeDundeeUK
| | - Johanna Ainsworth
- The MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life SciencesUniversity of DundeeDundeeUK
| | - Ryo Fujisawa
- The MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life SciencesUniversity of DundeeDundeeUK
| | - Constance Alabert
- Division of Molecular, Cell & Developmental Biology, School of Life SciencesUniversity of DundeeDundeeUK
| | - Karim PM Labib
- The MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life SciencesUniversity of DundeeDundeeUK
| |
Collapse
|
5
|
Lim Y, Tamayo-Orrego L, Schmid E, Tarnauskaite Z, Kochenova OV, Gruar R, Muramatsu S, Lynch L, Schlie AV, Carroll PL, Chistol G, Reijns MAM, Kanemaki MT, Jackson AP, Walter JC. In silico protein interaction screening uncovers DONSON's role in replication initiation. Science 2023; 381:eadi3448. [PMID: 37590370 PMCID: PMC10801813 DOI: 10.1126/science.adi3448] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 08/08/2023] [Indexed: 08/19/2023]
Abstract
CDC45-MCM2-7-GINS (CMG) helicase assembly is the central event in eukaryotic replication initiation. In yeast, a multi-subunit "pre-loading complex" (pre-LC) accompanies GINS to chromatin-bound MCM2-7, leading to CMG formation. Here, we report that DONSON, a metazoan protein mutated in microcephalic primordial dwarfism, is required for CMG assembly in vertebrates. Using AlphaFold to screen for protein-protein interactions followed by experimental validation, we show that DONSON scaffolds a vertebrate pre-LC containing GINS, TOPBP1, and DNA pol ε. Our evidence suggests that DONSON docks the pre-LC onto MCM2-7, delivering GINS to its binding site in CMG. A patient-derived DONSON mutation compromises CMG assembly and recapitulates microcephalic dwarfism in mice. These results unify our understanding of eukaryotic replication initiation, implicate defective CMG assembly in microcephalic dwarfism, and illustrate how in silico protein-protein interaction screening accelerates mechanistic discovery.
Collapse
Affiliation(s)
- Yang Lim
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute; Boston, MA 02115, USA
| | - Lukas Tamayo-Orrego
- MRC Human Genetics Unit, Institute of Genetics and Cancer, University of Edinburgh; Edinburgh, EH4 2XU, UK
| | - Ernst Schmid
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute; Boston, MA 02115, USA
| | - Zygimante Tarnauskaite
- MRC Human Genetics Unit, Institute of Genetics and Cancer, University of Edinburgh; Edinburgh, EH4 2XU, UK
| | - Olga V. Kochenova
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute; Boston, MA 02115, USA
- Howard Hughes Medical Institute; Boston, MA 02115, USA
| | - Rhian Gruar
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute; Boston, MA 02115, USA
| | - Sachiko Muramatsu
- Department of Chromosome Science, National Institute of Genetics, Research Organization of Information and Systems (ROIS); Mishima, Shizuoka 411-8540, Japan
| | - Luke Lynch
- Biochemistry Department, Stanford School of Medicine; Stanford, CA 94305, USA
| | - Aitana Verdu Schlie
- MRC Human Genetics Unit, Institute of Genetics and Cancer, University of Edinburgh; Edinburgh, EH4 2XU, UK
| | - Paula L. Carroll
- MRC Human Genetics Unit, Institute of Genetics and Cancer, University of Edinburgh; Edinburgh, EH4 2XU, UK
| | - Gheorghe Chistol
- Chemical and Systems Biology Department, Stanford School of Medicine; Stanford, CA 94305, USA
| | - Martin A. M. Reijns
- MRC Human Genetics Unit, Institute of Genetics and Cancer, University of Edinburgh; Edinburgh, EH4 2XU, UK
| | - Masato T. Kanemaki
- Department of Chromosome Science, National Institute of Genetics, Research Organization of Information and Systems (ROIS); Mishima, Shizuoka 411-8540, Japan
- Graduate Institute for Advanced Studies, SOKENDAI; Mishima, Shizuoka 411-8540, Japan
- Department of Biological Science, The University of Tokyo; Tokyo 113-0033, Japan
| | - Andrew P. Jackson
- MRC Human Genetics Unit, Institute of Genetics and Cancer, University of Edinburgh; Edinburgh, EH4 2XU, UK
| | - Johannes C. Walter
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute; Boston, MA 02115, USA
- Howard Hughes Medical Institute; Boston, MA 02115, USA
| |
Collapse
|