Biology subjects

Bourbon, H.-M.

Publications and source records attributed to Bourbon, H.-M..

4 recordsLinked to original sources

bioRxiv2022

Evolution and diversity of the TopoVI and TopoVI-like subunits with extensive divergence of the TOPOVIBL subunit

Type II DNA topoisomerases regulate topology by double-stranded DNA cleavage and ligation. The TopoVI family of DNA topoisomerase, first identified and biochemically characterized in Archaea, represents, with TopoVIII and mini-A, the type IIB family. TopoVI has several intriguing features in terms of function and evolution. TopoVI has been identified in some eucaryotes, and a global view is lacking to understand its evolutionary pattern. In addition, in eucaryotes, the two TopoVI subunits (TopoVIA and TopoVIB) have duplicated and evolved to give rise to Spo11 and TopoVIBL, forming TopoVI-like (TopoVIL), a complex essential for generating DNA breaks that initiation homologous recombination during meiosis. TopoVIL is essential for sexual reproduction. How the TopoVI subunits have evolved to ensure this meiotic function is unclear. Here, we investigated the phylogenetic conservation of TopoVI and TopoVIL. We demonstrate that BIN4 and RHL1, potentially interacting with TopoVIB, have co-evolved with TopoVI. Based on model structures, this observation supports the hypothesis for a role of TopoVI in decatenation of replicated chromatids and predicts that in eucaryotes the TopoVI catalytic complex includes BIN4 and RHL1. For TopoVIL, the phylogenetic analysis of Spo11, which is highly conserved among Eukarya, highlighted a eukaryal-specific N-terminal domain that may be important for its regulation. Conversely, TopoVIBL was poorly conserved and rapidly evolving, giving rise to ATP hydrolysis-mutated or -truncated protein variants, or was undetected in some species. This remarkable plasticity of TopoVIBL provides important information for the activity and function of TopoVIL during meiosis.

evolutionary biology↗

bioRxiv2021

TOPOVIBL-REC114 interaction regulates meiotic DNA double-strand breaks

Meiosis requires the formation of programmed DNA double strand breaks (DSBs), essential for fertility and for generating genetic diversity. DSBs are induced by the catalytic activity of the TOPOVIL complex formed by SPO11 and TOPOVIBL. To ensure genomic integrity, DNA cleavage activity is tightly regulated, and several accessory factors (REC114, MEI4, IHO1, and MEI1) are needed for DSB formation in mice. How and when these proteins act is not understood. Here, we show that REC114 is a direct partner of TOPOVIBL, and identified their conserved interacting domains by structural analysis. We then analysed the role of this interaction by monitoring meiotic DSBs in female and male mice carrying point mutations in TOPOVIBL that decrease or disrupt its binding to REC114. In these mutants, DSB activity was strongly reduced genome-wide in oocytes, and only in sub-telomeric regions in spermatocytes. In addition, in mutant spermatocytes, DSB activity was delayed in autosomes. These results provide evidence that REC114 is a key member of the TOPOVIL catalytic complex, and that the REC114/TOPOVIBL interaction ensures the efficiency and timing of DSB activity.

molecular biology↗

bioRxiv2021

C. elegans DSB-3 Reveals Conservation and Divergence among Protein Complexes Promoting Meiotic Double-Strand Breaks

Meiotic recombination plays dual roles in the evolution and stable inheritance of genomes: recombination promotes genetic diversity by reassorting variants, and it establishes temporary connections between pairs of homologous chromosomes that ensure for their future segregation. Meiotic recombination is initiated by generation of double-strand DNA breaks (DSBs) by the conserved topoisomerase-like protein Spo11. Despite strong conservation of Spo11 across eukaryotic kingdoms, auxiliary complexes that interact with Spo11 complexes to promote DSB formation are poorly conserved. Here, we identify DSB-3 as a DSB-promoting protein in the nematode Caenorhabditis elegans. Mutants lacking DSB-3 are proficient for homolog pairing and synapsis but fail to form meiotic crossovers. Lack of crossovers in dsb-3 mutants reflects a requirement for DSB-3 in meiotic DSB formation. DSB-3 concentrates in meiotic nuclei with timing similar to DSB-1 and DSB-2 (predicted homologs of yeast/mammalian Rec114/REC114), and DSB-1, DSB-2, and DSB-3 are interdependent for this localization. Bioinformatics analysis and interactions among the DSB proteins support the identity of DSB-3 as a homolog of MEI4 in conserved DSB-promoting complexes. This identification is reinforced by colocalization of pairwise combinations of DSB-1, DSB-2, and DSB-3 foci in structured illumination microscopy images of spread nuclei. However, unlike yeast Rec114, DSB-1 can interact directly with SPO-11, and in contrast to mouse REC114 and MEI4, DSB-1, DSB-2 and DSB-3 are not concentrated predominantly at meiotic chromosome axes. We speculate that variations in the meiotic program that have co-evolved with distinct reproductive strategies in diverse organisms may contribute to and/or enable diversification of essential components of the meiotic machinery. Significance StatementFaithful inheritance of chromosomes during meiosis depends on the formation and repair of double-strand DNA breaks (DSBs), which are generated through the activity of a topoisomerase-like protein known as Spo11. Spo11 exhibits strong conservation throughout eukaryotes, presumably reflecting constraints imposed by its biochemical activity, but auxiliary proteins that collaborate with Spo11 to promote and regulate DSB formation are less well conserved. Here we investigate a cohort of proteins comprising a complex required for meiotic DSB formation in Caenorhabditis elegans, providing evidence for both conservation with and divergence from homologous complexes in other organisms. This work highlights the evolutionary malleability of protein complexes that serve essential, yet auxiliary, roles in fundamental biological processes that are central to reproduction.

genetics↗

bioRxiv2020

Mediator complex subunit Med19 binds directly GATA DNA-binding zinc finger and functions with Med1 in GATA-driven gene regulation in vivo

The evolutionarily-conserved multiprotein Mediator complex (MED) serves as an interface between DNA-bound transcription factors (TFs) and the RNA Polymerase II machinery. It has been proposed that each TF interacts with a dedicated MED subunit to induce specific transcriptional responses. However, binary MED subunit - TF partnerships are probably oversimplified models. Using Drosophila TFs of the GATA family - Pannier (Pnr) and Serpent (Srp) - as a model, we have previously established GATA cofactor evolutionarily-conserved function for the Med1 Mediator subunit. Here, we show that another subunit, Med19, is required for GATA-dependent gene expression and interacts physically with Pnr and Srp in cellulo, in vivo and in vitro through their conserved C-zinc finger (ZF), indicating general GATA co-activator functions. Interestingly, Med19 is critical for the regulation of all tested GATA target genes which is not the case for Med1, suggesting differential use of MED subunits by GATAs depending on the target gene. Lastly, despite their presumed distant position within the MED middle module, both subunits interact physically. In conclusion, our data shed new light first on the MED complex, engaging several subunits to mediate TF-driven transcriptional responses and second, on GATA TFs, showing that ZF DNA-binding domain also serves for transactivation.

developmental biology↗