Biology subjects

Flaus, A.

Publications and source records attributed to Flaus, A..

6 recordsLinked to original sources

bioRxiv2025

AEBP2-Directed H3K27me2 Defines a Specific Vulnerability in EZH2-mutant Lymphoma

The catalytic subunit of Polycomb Repressive Complex 2 (PRC2), EZH2, is recurrently mutated in 25% of diffuse large B-cell lymphomas (DLBCL), causing increased H3K27me3 and decreased H3K27me2 levels. EZH2 inhibitors provide clinical benefit, but resistance frequently develops, highlighting the need for alternative therapeutic targets. Here, we identify the PRC2 accessory protein AEBP2 as a specific genetic dependency in EZH2-mutant DLBCL. While AEBP2 acts through PRC2, its essential role is surprisingly independent of canonical H3K27me3-mediated gene silencing. Instead, AEBP2 functions within a PRC2.2 complex lacking JARID2, using its zinc-finger domains to sample intergenic chromatin to sustain H3K27me2. Notably, loss of AEBP2 or NSD2 caused contrasting changes in intergenic H3K27me2 levels, driving sensitivity or resistance to PRC2 inhibitors, respectively. Our findings identify AEBP2-PRC2.2-maintained intergenic H3K27me2 as a therapeutic vulnerability in EZH2-mutant DLBCL and highlight dysregulated H3K27me2 as an underappreciated form of PRC2 dysfunction in cancer, with important therapeutic implications.

cancer biology↗

bioRxiv2024

Thalamic blood flow and EEG frequency band power during hyperventilation in idiopathic generalized epilepsy

Absence seizures in idiopathic generalised epilepsy (IGE) involve thalamo-cortical circuits. Hyperventilation (HV) is a standard technique to trigger epileptiform discharges and absence seizures in IGE. HV also increases electroencephalography (EEG) delta band power and decreases global cerebral blood flow (CBF). The relationships between HV, EEG band power, and regional CBF have not been investigated in the same patients at the same time. We compared the effects of hyperventilation between 13 individuals with IGE and 18 healthy controls on thalamic CBF assessed with pseudo-continuous Arterial Spin Labelling (pCASL) simultaneously to EEG frequency band power during three periods of hyperventilation interleaved with three periods of rest, normalised to each participants pre-HV values. Pre-HV, there were no differences between patients and controls. During the three rest periods combined, patients had higher normalised respiratory rates but no difference in CBF or EEG band power compared with controls. During HV, CBF decreases were similar in controls and IGE patients in cortical gray matter (37.1{+/-}1.3% in controls, 37.9{+/-}2.0% in patients) and basal ganglia (35.6{+/-}2.0% in controls, 33.3{+/-}2.3% in patients). In the thalamus, CBF decreased by 35.5{+/-}1.9% in controls, but only by 27.1{+/-}2.5% in patients (p=0.011). Delta band power increased by 42% in patients, but only by 27% in patients (p<0.045). Both controls and patients thalamic CBF significantly decreased as a function of respiratory rate, but the relationship was weaker in patients (rho -0.38 [0.95 confidence interval lower limit -0.629; upper limit -0.059] vs -0.51 [-0.698; -0.255] in controls). Delta power correlated with thalamic CBF only in controls (rho -0.21 [-0.388; -0.017]) but not in patients (rho -0.1 [-0.345; 0.157]). EEG power and respiratory rate were not significantly correlated in either group. This first study of the interrelationships between HV, blood flow, and EEG band power suggests that regional thalamic abnormalities of blood flow regulation, or a neurophysiological abnormality leading to smaller reactive blood flow changes, may underlie HV-associated EEG activation. Graphical abstract textIn this first investigation of combined hyperventilation, blood flow and EEG band power measurements in idiopathic generalised epileptic patients and healthy subjects, we revealed that localized thalamic blood flow regulatory problems or neurophysiological disorders caused minor reactive blood flow variations and may cause hyperventilation-associated EEG activation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=182 SRC="FIGDIR/small/586742v1_ufig1.gif" ALT="Figure 1"> View larger version (58K): org.highwire.dtl.DTLVardef@12a5ebeorg.highwire.dtl.DTLVardef@b22944org.highwire.dtl.DTLVardef@b335dforg.highwire.dtl.DTLVardef@195c5e2_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2024

Moonlighting on the Fasciola hepatica tegument: enolase, a glycolytic enzyme, interacts with the extracellular matrix and fibrinolytic system of the host

Enolase is a 47 kDa enzyme that functions within the glycolysis and gluconeogenesis pathways involved in the reversible conversion of D-2-phosphoglycerate (2PGA) to phosphoenolpyruvate (PEP). However, in the context of host-pathogen interactions, enolase from different species of parasites, fungi and bacteria have been shown to contribute to adhesion processes by binding to proteins of the host extracellular matrix (ECM), such as fibronectin (FN) or laminin (LM). In addition, enolase is a plasminogen (PLG)-binding protein and induces its activation to plasmin, the main protease of the host fibrinolytic system. These secondary moonlighting functions of enolase are suggested to facilitate pathogen migration through host tissues. This study aims to uncover the moonlighting role of enolase from the parasite Fasciola hepatica, shedding light on its relevance to host-parasite interactions in fasciolosis, a global zoonotic disease of increasing concern. A purified recombinant form of F. hepatica enolase (rFhENO), functioning as an active homodimeric glycolytic enzyme of [~]94 kDa, was successfully obtained, fulfilling its canonical role. Immunoblotting studies on adult worm extracts showed that the enzyme is present in the tegument and the excretory/secretory products of the parasite, which supports its key role at the host-parasite interface. Confocal immunolocalisation studies of the protein in newly excysted juveniles and adult worms also localised its expression within the parasite tegument. Finally, we showed by ELISA that rFhENO can act as a parasitic adhesin by binding host LM, but not FN. rFhENO also binds PLG and enhances its conversion to plasmin in the presence of the tissue-type and urokinase-type PLG activators (t-PA and u-PA). This moonlighting adhesion-like function of the glycolytic protein enolase could contribute to the mechanisms by which F. hepatica efficiently invades and migrates within its host and encourages further research efforts that are designed to impediment this function by vaccination or drug design. AUTHOR SUMMARYFasciola hepatica is a parasitic worm causing fasciolosis, primarily affecting herbivorous mammals and posing a significant veterinary problem. Furthermore, it is a zoonosis, meaning it can be transmitted to humans. F. hepatica enters the definitive host through ingestion of contaminated aquatic plants, migrating through the intestine to settle in the liver bile ducts, where it matures into the adult stage. To migrate, it utilizes various invasion strategies, including the use of multifunctional proteins, known as moonlighting. In this study, we produced and molecularly characterized the parasitic enzyme enolase as a moonlighting protein to understand F. hepatica invasion mechanisms. We produced recombinant enolase with glycolytic activity, its canonical function in parasite energy production. Additionally, we localised this enzyme in the parasites tegument, in direct contact with the host, and demonstrated its ability to elicit an immune response early in ovine infection. Finally, we demonstrated the ability of enolase to interact with the extracellular matrix and the hosts fibrinolysis, a proteolytic system responsible for dissolving blood clots. These secondary functions of F. hepatica enolase, described here for the first time, along with its localisation and immunogenicity, suggest this protein as an interesting antigen for fasciolosis diagnosis and/or control.

molecular biology↗

bioRxiv2021

Hydrozoan sperm-specific H2B histone variants stabilize chromatin and block transcription without enhancing chromatin condensation

Many animals achieve sperm chromatin compaction and stabilisation during spermatogenesis by replacing canonical histones with sperm nuclear basic proteins (SNBPs) such as protamines. A number of animals including hydrozoan cnidarians and echinoid sea urchins lack protamines and have instead evolved a distinctive family of sperm-specific histone H2Bs (spH2Bs) with extended N-termini rich in SPKK-related motifs. Sperm packaging in echinoids such as sea urchins is regulated by spH2Bs and their sperm is negatively buoyant for fertilization on the sea floor. Hydroid cnidarians also package sperm with spH2Bs but undertake broadcast spawning and their sperm properties are poorly characterised. We show that sperm chromatin from the hydroid Hydractinia possesses higher stability than its somatic equivalent, with reduced accessibility of sperm chromatin to transposase Tn5 integration in vivo and to endonucleases in vitro. However, nuclear dimensions are only moderately reduced in mature Hydractinia sperm compared to other cell types. Ectopic expression of spH2B in the background of H2B knockdown resulted in downregulation of global transcription and cell cycle arrest in embryos without altering their nuclear density. Taken together, spH2B variants containing SPKK-related motifs act to stabilise chromatin and silence transcription in Hydractinia sperm without significant chromatin compaction. This is consistent with a contribution of spH2B to sperm buoyancy as a reproductive adaptation.

developmental biology↗

bioRxiv2021

Histone sequence variation in divergent eukaryotes facilitates diversity in chromatin packaging

The histone proteins defining nucleosome structure are highly conserved in common model organisms and are frequently portrayed as uniform chromatin building blocks. We surveyed over 1700 complete eukaryotic genomes and confirm that almost all encode recognisable canonical core histones. Nevertheless, divergent eukaryotes show unrecognised diversity in histone sequences and offer an opportunity to observe the potential for nucleosome variation. Recombinant histones for Plasmodium falciparum, Giardia lamblia, Encephalitozoon cuniculi and Leishmania major were prepared alongside those for human, Xenopus laevis and Saccharomyces cerevisiae. All could be assembled into nucleosomes in vitro on sequences known to direct positioning with metazoan histones. P. falciparum histones refolded into very stable nucleosomes consistent with a highly regulated transcriptional programme. In contrast, G. lamblia and E. cuniculi histones formed less stable nucleosomes and were prone to aggregation as H3-H4 tetramers. Inspection of the histone fold dimer interface residues suggested a potential to form tetrasomal arrays consistent with polymerisation. DNA binding preferences observed using systematic evolution of ligands by exponential enrichment (SELEX) for human, P. falciparum and E. cuniculi histone octamers were highly similar and reflect a shared capability to package diverse genomic sequences. This demonstrates that nucleosomal organisation is retained across eukaryotes and can accommodate genome variation, but histone protein sequences vary more than commonly recognised to provide the potential for diversity of chromatin features. Significance statementIt is widely assumed that eukaryotes package their genomes using equivalent nucleosome building blocks despite considerable variation in the composition and behaviour of cell nuclei. Our survey of available eukaryote genomes shows that histone proteins from divergent eukaryotes vary much more widely in sequence than is commonly recognised, even in histone fold dimer and DNA interaction interfaces. We demonstrate that divergent eukaryote histones nevertheless form nucleosomes on DNA sequences favoured in metazoans. These nucleosomes vary in stability but share broad DNA sequence preferences. This suggests that histone-dependent packaging does not constrain genome variation, and that chromatin behaviour can adapt by evolution of canonical core histone sequences in addition to other well-known mechanisms.

biochemistry↗

bioRxiv2019

The Human Canonical Core Histone Catalogue

Core histone proteins H2A, H2B, H3, and H4 are encoded by a large family of genes distributed across the human genome. Canonical core histones contribute the majority of proteins to bulk chromatin packaging, and are encoded in 4 clusters by 65 coding genes comprising 17 for H2A, 18 for H2B, 15 for H3, and 15 for H4, along with at least 17 total pseudogenes. The canonical core histone genes display coding variation that gives rise to 11 H2A, 15 H2B, 4 H3, and 2 H4 unique protein isoforms. Although histone proteins are highly conserved overall, these isoforms represent a surprising and seldom recognised variation with amino acid identity as low as 77% between canonical histone proteins of the same type. The gene sequence and protein isoform diversity also exceeds commonly used subtype designations such as H2A.1 and H3.1, and exists in parallel with the well-known specialisation of variant histone proteins. RNA sequencing of histone transcripts shows evidence for differential expression of histone genes but the functional significance of this variation has not yet been investigated. To assist understanding of the implications of histone gene and protein diversity we have catalogued the entire human canonical core histone gene and protein complement. In order to organise this information in a robust, accessible, and accurate form, we applied software build automation tools to dynamically generate the canonical core histone repertoire based on current genome annotations and then to organise the information into a manuscript format. Automatically generated values are shown with a light grey background. Alongside recognition of the encoded protein diversity, this has led to multiple corrections to human histone annotations, reflecting the flux of the human genome as it is updated and enriched in reference databases. This dynamic manuscript approach is inspired by the aims of reproducible research and can be readily adapted to other gene families.

molecular biology↗