Biology subjects

Bouscasse, E.

Publications and source records attributed to Bouscasse, E..

4 recordsLinked to original sources

bioRxiv2026

SAD-6/ATRX enables broad genome surveillance and defense in fungi

The chromatin remodeler ATRX and its orthologs maintain genome function by regulating repetitive DNA and dynamic chromatin, and their activities have been canonically associated with replication-independent deposition of the histone H3.3 variant. This model is difficult to reconcile with fungi, which encode ATRX orthologs but lack H3 variants that may separately support replication-coupled and replication-independent deposition. Here we show that the fungal ATRX ortholog SAD-6 instead relies on a highly divergent histone H4 variant (H4v) to mediate broad genome surveillance and defense. Deposition of H4v is strictly SAD-6-dependent and thus provides a sensitive genome-wide readout of SAD-6 activity, revealing its functions at telomeres, tRNA and rDNA loci, AT-rich DNA, artificial transgenes, decaying mobile elements, and many genic regions. We further show that SAD-6 is required for a pathway of repeat-induced point mutation (RIP) that also requires DIM-5, a conserved SUV39 methyltransferase that mediates trimethylation of histone H3 lysine-9 in heterochromatin. Together, these findings establish ATRX-like remodelers as broad regulators of genome surveillance and defense in fungi that act through a highly divergent histone H4 variant rather than H3.3. Given that RIP is proposed to recognize repetitive DNA via recombination-independent homologous pairing, the requirement for SAD-6 in RIP suggests that ATRX-like remodelers may couple DNA pairing to heterochromatin nucleation on repeats.

molecular biology↗

bioRxiv2026

Stress-responsive Mycobacterium tuberculosis subpopulations manipulate macrophage polarization and can be targeted to limit inflammation

Tuberculosis is characterized by broad clinical heterogeneity that hinders infection control, with differences in lesion development, progression, and treatment outcomes. This complexity is likely associated with Mycobacterium tuberculosis inherent phenotypic variation and its capacity to diversify under host microenvironmental and antimicrobial stressors. Here, we analyze M. tuberculosis at the single-cell and subpopulation level using fluorescent reporters, imaging, transcriptomic, and functional assays. We identify RNA signatures specific to stress-responsive bacilli with translational potential. Focusing on the clinically validated chaperone GroEL2, we find that it correlates with M. tuberculosis growth rate and stress tolerance in vitro and intracellularly. Furthermore, GroEL2 phenotypic diversity influences innate responses in macrophages, which experience different polarization, in turn affecting GroEL2 expression. We also show that targeting GroEL2 impairs pathogen survival and dampens inflammation. This study provides a link between pathogen phenotypic variation and macrophage fates, with implications for early infection outcomes, local disease progression, and subpopulation-targeted interventions.

microbiology↗

bioRxiv2026

A Seven-Protein Assembly Promotes Stability, Neutralisation and Secretion of the T7SSb LXG-effector TelE

Streptococcus gallolyticus subsp. gallolyticus (SGG) is a gut pathobiont associated with colorectal cancer. Like many Firmicutes, SGG utilizes a specialized Type VII Secretion System (T7SSb) to export WXG100 and LXG proteins, the latter involved in bacterial competition. We previously identified TelE, an LXG protein whose C-terminus mediates membrane pore formation in Escherichia coli. In SGG UCN34, TelE (Gallo_0562) is co-expressed with six proteins (Gallo_0559 to Gallo_0565), including its immunity protein TipE (Gallo_0565). Here we show that the absence of those co-expressed proteins affects TelE stability and secretion. These proteins associate with TelE to form a soluble and stable seven-protein complex. Gallo_0559 and Gallo_0560 interact with the N-terminal LXG domain of TelE, Gallo_0561 binds to its central region, while the six-transmembrane protein Gallo_0563, together with Gallo_0564 and TipE associates with its C-terminal domain. These findings describe a new modular complex that stabilizes TelE while reducing its toxicity and optimizing its T7SSb-mediated delivery.

microbiology↗

bioRxiv2025

A novel approach to tagging tubulin reveals microtubule assembly dynamics of the axoneme in Trypanosoma brucei

The protozoan parasite Trypanosoma brucei is a mono-flagellated cell during the G1-phase of its cell cycle. In order to duplicate, it assembles a new flagellum alongside the mature one, in which further elongation is prevented. Our group proposed a model where the mature flagellum is locked after construction to full length (Bertiaux et al. 2018) and access of new building blocks for elongation is exclusive to the new flagellum. To test this hypothesis directly, we developed a tool for the inducible expression of tagged tubulin. Alpha-tubulin that was tagged with an intragenic Ty-1-epitope behaved indistinguishable from untagged tubulin. Its incorporation was monitored after inducible expression, to follow the assembly dynamics of microtubules in the cell body, the mitotic spindle and the flagellum. In this study we observed that integration of tubulin occurs at the distal flagellum tip at a linear rate and is indeed restricted to the new flagellum in bi-flagellated cells. This is direct evidence that trypanosomes avoid competition between the two flagella by allowing tubulin incorporation only in the new organelle. However, by tracing flagella over several cell cycles we could also show that mature flagella do not remain locked indefinitely. The restriction is lifted briefly after the bi-flagellated cell has divided and the daughter cell inheriting the old flagellum shows incorporation of newly synthesized building blocks again. It then has to lock again before the cell can assemble a new flagellum. Our findings suggest regular incorporation of tubulin at the tip of previously locked flagella. This evidence was supported with an orthogonal approach, with which we monitored the incorporation of HaloTag-tagged radial spoke protein 4/6. Since flagellum length in trypanosomes is stable, this indicates that the entire axoneme is subject to regular events of transient disassembly followed by assembly at its distal tip.

cell biology↗