Compaction and resolution of replicated chromosomes into morphologically and spatially distinct sister chromatids is essential for faithful DNA segregation in all organisms, but the molecular mechanisms that underlie these processes are poorly understood. In bacteria, chromosome segregation is largely driven by DNA compaction, which is thought to occur by the orderly folding of chromosomes along adjacent DNA segments drawing replicated sisters in on themselves and away from each other. In virtually all organisms, Structural Maintenance of Chromosomes (SMC) condensin complexes play a central role in this process but how these ring-shaped ATPase function has remained unclear. In Bacillus subtilis, condensin rings are topologically loaded onto the chromosome adjacent to the origin of replication by the partitioning protein ParB bound to centromeric parS sites. Using chromosome conformation capture (Hi-C) and ChIP-seq, we discovered that these complexes then travel down the left and right chromosome arms all the way to the terminus while tethering the two arms together. Our findings support a generalizable model in which SMC complexes act along adjacent DNA segments by processively enlarging DNA loops. In this model, these ring-shaped complexes encircle the DNA flanking their loading site, tethering the duplexes together. As these tethers move away from their loading sites they generate loops. Loop- formation ensures that these complexes act along adjacent DNA segments and therefore resolve rather than tangle sister chromosomes. In B. subtilis, processive loop enlargement centered on origin-proximal parS sites draws sister origins in on themselves and away from each other. De novo loop formation along chromosome arms in eukaryotes can also explain how condensin complexes compact and resolve sister chromatids during mitosis and provides a mechanism for the formation of transcriptionally insulated domains (also called topologically associated domains or TADs) by SMC cohesin complexes during interphase. Our studies on the B. subtilis SMC complex highlights the importance of using simple model systems to study conserved cell biological processes. The experiments described in this proposal build on our recent discoveries and preliminary findings to define how these broadly conserved complexes generate DNA loops; how these ring- shaped tethers are removed when they reach the replication terminus; and the role of condensin in remodeling the bacterial chromosome during the replication-segregation cycle.

Public Health Relevance

In this proposal we investigate how Structural Maintenance of Chromosome (SMC) complexes remodel chromosomes by processively enlarging DNA loops. Mutations in the SMC cohesin complex are associated with human multi-spectrum developmental abnormalities termed cohesinopathies and mutations in SMC condensin complexes have been associated with T-cell lymphomas and colon cancer. A greater understanding of SMC complex function has the potential to provide insight into the underlying mechanisms of cohesinopathies and to identify possible therapeutic targets for a subset of cancers.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM086466-11
Application #
9983491
Study Section
Prokaryotic Cell and Molecular Biology Study Section (PCMB)
Program Officer
Janes, Daniel E
Project Start
2009-08-01
Project End
2022-05-31
Budget Start
2020-06-01
Budget End
2021-05-31
Support Year
11
Fiscal Year
2020
Total Cost
Indirect Cost
Name
Harvard Medical School
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
047006379
City
Boston
State
MA
Country
United States
Zip Code
02115
Wang, Xindan; Hughes, Anna C; Brandão, Hugo B et al. (2018) In Vivo Evidence for ATPase-Dependent DNA Translocation by the Bacillus subtilis SMC Condensin Complex. Mol Cell 71:841-847.e5
Ramírez-Guadiana, Fernando H; Meeske, Alexander J; Wang, Xindan et al. (2017) The Bacillus subtilis germinant receptor GerA triggers premature germination in response to morphological defects during sporulation. Mol Microbiol 105:689-704
Wang, Xindan; Brandão, Hugo B; Le, Tung B K et al. (2017) Bacillus subtilis SMC complexes juxtapose chromosome arms as they travel from origin to terminus. Science 355:524-527
Rodrigues, Christopher D A; Henry, Xavier; Neumann, Emmanuelle et al. (2016) A ring-shaped conduit connects the mother cell and forespore during sporulation in Bacillus subtilis. Proc Natl Acad Sci U S A 113:11585-11590
Widderich, Nils; Rodrigues, Christopher D A; Commichau, Fabian M et al. (2016) Salt-sensitivity of ?(H) and Spo0A prevents sporulation of Bacillus subtilis at high osmolarity avoiding death during cellular differentiation. Mol Microbiol 100:108-24
Wang, Xindan; Montero Llopis, Paula (2016) Visualizing Bacillus subtilis During Vegetative Growth and Spore Formation. Methods Mol Biol 1431:275-87
Wang, Xindan; Le, Tung B K; Lajoie, Bryan R et al. (2015) Condensin promotes the juxtaposition of DNA flanking its loading site in Bacillus subtilis. Genes Dev 29:1661-75
Meeske, Alexander J; Sham, Lok-To; Kimsey, Harvey et al. (2015) MurJ and a novel lipid II flippase are required for cell wall biogenesis in Bacillus subtilis. Proc Natl Acad Sci U S A 112:6437-42
Wang, Xindan; Tang, Olive W; Riley, Eammon P et al. (2014) The SMC condensin complex is required for origin segregation in Bacillus subtilis. Curr Biol 24:287-92
Wang, Xindan; Montero Llopis, Paula; Rudner, David Z (2014) Bacillus subtilis chromosome organization oscillates between two distinct patterns. Proc Natl Acad Sci U S A 111:12877-82

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