Biology subjects

Ricci, E. P.

Publications and source records attributed to Ricci, E. P..

15 recordsLinked to original sources

bioRxiv2026

The rapid delivery of RNase H variants reveals distinct classes of RNA:DNA hybrids

Multiple lines of evidence suggest that RNase H1-sensitive RNA:DNA hybrids (thereafter referred to as hybrids) could disrupt the stability and restart of stalled replication forks. The prolonged over-expression of RNase H1 is the most popular method to manipulate hybrids in situ but it cannot discriminate between direct and indirect effects resulting from their loss. To overcome this limitation, we developed iCoRD (in Cellulo RNase H Delivery) to rapidly deliver comparable amounts of either Escherichia coli RNase H1 (RnhA) or control proteins in live cells, with a negligible impact on the transcriptome. iCoRD-delivered RnhA recognises hybrids in situ, is enriched in the vicinity of active replication forks and rescues replication fork progression in different stress conditions. While iCoRD-delivered RnhA had a clear impact on stress-induced, fork-proximal hybrids and R-ChIP signals, it had no effect on DRIP or S9.6 Cut&Tag signals, even when these were induced by stress. Our results strongly suggest the existence of distinct populations of hybrids that are best mapped by different methods and are differently sensitive to RNase H1 activity in situ.

molecular biology↗

bioRxiv2025

SNX-BAR proteins 5 and 6 are required for NCOA7-AS antiviral activity against influenza A virus

Interferon-induced antiviral proteins act on the first line of defence against viruses, including influenza A virus (IAV). Among those, the short isoform of Nuclear Receptor Coactivator 7 (NCOA7-AS) has been shown to inhibit IAV entry and more especially the fusion between endosomal and viral membranes. Ectopic expression of NCOA7-AS leads to the increased acidification of the endolysosomal pathway, putatively through NCOA7-AS interaction with the vacuolar ATPase (V-ATPase). However, the precise mechanism of action of NCOA7-AS is not fully understood. Here, we identified the cellular partners of NCOA7-AS by mass spectrometry, including the V-ATPase subunits known to interact with NCOA7-AS. A point mutation disrupting the interaction with the V-ATPase led to loss of antiviral activity against IAV, demonstrating that V-ATPase engagement is required for the antiviral phenotype. Moreover, sorting nexin (SNX) 1/2/5/6 were identified as novel partners of NCOA7-AS. These proteins are involved in retrograde transport of cellular cargoes from endosomes to the trans-Golgi network. We revealed that SNX5/6 interacted directly with NCOA7-AS and were essential for NCOA7-AS antiviral activity against IAV. Interestingly, crystal structures of NCOA7-AS/SNX5 complexes showed that the SNX5-interaction motif in NCOA7-AS was similar to those found in known cargoes of SNX5/6. In addition, we could pinpoint several critical residues that were important for binding and antiviral activity. Collectively, our study identifies novel essential partners for NCOA7-AS antiviral activity and the structural basis for their interaction.

microbiology↗

bioRxiv2025

Rapid delivery of RNase H1 enables replication fork progression under stress independently of R-loop resolution

The over-expression of RNase H1 enables the progression of replication forks under stress and safeguards genome stability. The most common interpretation of these observations is that RNase H1 over-expression removes R-loops, whose formation would hinder replication fork progression. Here we challenge this model using an innovative strategy to rapidly deliver ready-made Escherichia coli RNase H1 (RnhA) in live cells. We show that RnhA is enriched in the vicinity of active replication forks and that it rescues replication fork progression in different stress conditions. However, RnhA had no impact on R-loops mapped by the DRIP or Cut&Tag methods. Our results reveal the existence of distinct populations of RNA:DNA hybrids that are differently sensitive to RnhA and invites new interpretations of well-established observations. HIGHLIGHTSO_LIRapid delivery of R-loop sensors and regulators in live cells C_LIO_LIRapid delivery of RnhA rescues replication fork progression in stress conditions C_LIO_LIRapid delivery of RnhA does not impact R-loops C_LIO_LIDRIP detects RNA:DNA species insensitive to RNase H1 in cells C_LI

molecular biology↗

bioRxiv2024

Unveiling novel conserved HIV-1 open reading frames encoding T cell antigens using ribosome profiling.

The development of ribosomal profiling (Riboseq) revealed the immense coding capacity of human and viral genomes. Here, we used Riboseq to delineate the first translatome of HIV-1 in infected CD4+ T cells. In addition to canonical viral protein coding sequences (CDSs), we identify 98 alternative open reading frames (ARFs), corresponding to small Open Reading Frames (sORFs) that are distributed across the HIV genome including the UTR regions. Using a database of HIV genomes, we observed that most ARF amino-acid sequences are likely conserved among clade B and C of HIV-1, with 8 ARF-encoded amino-acid sequences being more conserved than the overlapping CDSs. Using T cell-based assays and mass spectrometry-based immunopeptidomics, we demonstrate that ARFs encode viral polypeptides. In the blood of HIV-infected individuals, ARF-derived peptides elicit potent poly-functional T cell responses mediated by both CD4+ and CD8+ T cells. Our discovery expands the list of conserved viral polypeptides that are targets for vaccination strategies and might reveal the existence of viral microproteins or pseudogenes.

immunology↗

bioRxiv2024

Human MX1 induces the cytoplasmic sequestration of neo-synthesized influenza A virus vRNPs

Interferon-inducible Myxovirus resistance 1 (MX1) proteins are well-known to restrict influenza A virus (IAV) at early stages during viral replication, impairing the viral transcription/replication process. Herein, we show that this early restriction was only partial against human IAVs, whereas a strong inhibition of viral production was observed. Indeed, relatively high levels of IAV mRNAs and proteins were observed in the presence of human (Hs) and mouse (Mm) MX1 proteins but additional inhibition processes occurred at later stages of IAV life cycle. Hence, MmMx1 induced an abnormal nuclear accumulation of the viral nucleoprotein (NP) at late time points post-infection. This block was also observed, albeit to a much lower extent, with HsMX1. In most HsMX1-expressing cells, vRNPs could be exported from the nucleus to the cytoplasm however a potent defect in subsequent vRNP cytoplasmic trafficking was observed. Indeed, vRNPs were found sequestrated together with cellular co-factors YBX1 and Rab11a in large clusters in the vicinity of the microtubule organization center (MTOC). Live imaging experiments revealed that the transient association of HsMX1 with Rab11a-associated vRNPs favoured their dynein-dependant retrograde transport along microtubules towards the MTOC. Importantly, dynein inhibition prevented the vRNP sequestration and significantly rescued infectious viral production in the presence of HsMX1, showing a significant contribution of these abnormal vRNP clusters in HsMX1 antiviral activity. In conclusion, this study provides the first evidence of IAV vRNPs being re-routed and accumulated away from the plasma membrane, through the coordinated action of HsMX1 restriction factor, dynein and the microtubule network.

microbiology↗

bioRxiv2023

Metabolism-dependent secondary effect of anti-MAPK cancer therapy on DNA repair

Amino acid bioavailability impacts mRNA translation in a codon depending manner. Here, we report that the anti-cancer MAPK inhibitors (MAPKi) decrease the intracellular concentration of aspartate and glutamate in melanoma cells. This results in the accumulation of ribosomes on codons corresponding to these amino acids and triggers the translation-dependent degradation of mRNAs encoding aspartate- and glutamate-rich proteins mostly involved in DNA metabolism. Consequently, cells that survive to MAPKi degrade aspartate and glutamate to generate energy, which simultaneously decreases their needs in amino acids owing to the downregulation of aspartate- and glutamate-rich proteins involved in cell proliferation. Concomitantly, the downregulation of aspartate- and glutamate-rich proteins involved in DNA repair increases DNA damage loads. Thus, DNA repair defects, and therefore mutations, are, at least in part, a secondary effect of the metabolic adaptation of cells exposed to MAPKi.

cancer biology↗

bioRxiv2023

Incorporation of genome-bound cellular proteins into HIV-1 particles regulates viral infection

The initial steps of the human immunodeficiency virus 1 (HIV-1) lifecycle are regulated by cellular RNA-binding proteins (RBPs). To understand the scope of these early host-virus interactions, we developed in virion RNA interactome capture (ivRIC), which allowed the comprehensive and systematic profiling of the proteins that interact with the HIV-1 genomic (g)RNA inside viral particles. ivRIC identified 104 cellular RBPs within the encapsidated HIV-1 ribonucleoprotein, many of which are typically found in the cellular nucleus. Notably, these nuclear RBPs interact with the HIV-1 RBP Rev, suggesting that they associate with HIV-1 gRNA during its nuclear life. Functional assays show that ivRBPs are important for HIV-1, including PURA and PURB, which control viral gene expression and infectivity through interaction with critical sequences in the gRNA. Our characterisation of the composition of the encapsidated ribonucleoprotein of HIV-1 uncovers new host-virus interactions that invokes new mechanisms for controlling HIV-1 infection.

molecular biology↗

bioRxiv2023

Stable Structures or poly(A)-binding protein loading protect cellular and viral RNAs against ISG20-mediated decay

ISG20 is an interferon-induced 3-to-5 RNA exonuclease that acts as a broad antiviral factor. At present, the features that expose RNA to ISG20 remain unclear, although recent studies have pointed to the modulatory role of epitranscriptomic modifications in the susceptibility of target RNAs to ISG20. These findings raise the question as to how cellular RNAs, on which these modifications are abundant, cope with ISG20. To obtain an unbiased perspective on this topic, we used RNAseq and biochemical assays to identify elements that regulate the behavior of RNAs against ISG20. The results we have obtained indicate that poly(A)-binding protein (PABP1) loading on the RNA 3 tail provides a primal protection against ISG20, easily explaining the overall protection of cellular mRNAs observed by RNAseq. The second element we uncovered is provided by terminal stem-loop RNA structures, that have been associated to ISG20 protection before, but that we re-examine here systematically to define the stabilities that tilt the balance between resistance and susceptibility to ISG20. Given that these elements are present on cellular mRNAs, but can be co-opted by viruses as well, these results shed new light on the complex interplay that regulates the susceptibility of different classes of viruses against ISG20.

microbiology↗

bioRxiv2021

Coupled protein synthesis and ribosome-guided piRNA processing on mRNAs

PIWI-interacting small RNAs (piRNAs) protect the germline genome and are essential for fertility. Previously, we showed that ribosomes guide the biogenesis of piRNAs from long non-coding RNAs (lncRNAs) after translating the short open reading frames (ORFs) near their 5 cap. It remained unclear, however, how ribosomes proceed downstream of ORFs and how piRNA precursors distinguish from other RNAs. It is thus important to test whether a short ORF length is required for substrate recognition for ribosome guided-piRNA biogenesis. Here, we characterized a poorly understood class of piRNAs that originate from the 3 untranslated regions (3UTRs) of protein coding genes in mice and chickens. We demonstrate that their precursors are full-length mRNAs and that post-termination 80S ribosomes guide piRNA production on 3UTRs after translation of upstream long ORFs. Similar to non-sense mediated decay (NMD), piRNA biogenesis degrades mRNA right after pioneer rounds of translation and fine-tunes protein production from mRNAs. Interestingly, however, we found that NMD, along with other surveillance pathways for ribosome recycling are temporally sequestered during the pachytene stage to allow for robust piRNA production. Although 3UTR piRNA precursor mRNAs code for distinct proteins in mice and chickens, they all harbor embedded transposable elements (TEs) and produce piRNAs that cleave TEs, suggesting that TE suppression, rather than the function of proteins, is the primary evolutionary force maintaining a subset of mRNAs as piRNA precursors. Altogether, we discover a function of the piRNA pathway in fine-tuning protein production and reveal a conserved, general piRNA biogenesis mechanism that recognizes translating RNAs regardless of their ORF length in amniotes.

molecular biology↗

bioRxiv2021

RSL24D1 sustains steady-state ribosome biogenesis and pluripotency translational programs in embryonic stem cells.

Embryonic stem cell (ESC) fate decisions are regulated by a complex molecular circuitry that requires tight and coordinated gene expression regulations at multiple levels from chromatin organization to mRNA processing. Recently, ribosome biogenesis and translation have emerged as key regulatory pathways that efficiently control stem cell homeostasis. However, the molecular mechanisms underlying the regulation of these pathways remain largely unknown to date. Here, we analyzed the expression, in mouse ESCs, of over 300 genes involved in ribosome biogenesis and we identified RSL24D1 as the most differentially expressed between self-renewing and differentiated ESCs. RSL24D1 is highly expressed in multiple mouse pluripotent stem cell models and its expression profile is conserved in human ESCs. RSL24D1 is associated with nuclear pre-ribosomes and is required for the maturation and the synthesis of 60S subunits in mouse ESCs. Interestingly, RSL24D1 depletion significantly impairs global translation, particularly of key pluripotency factors, including POU5F1 and NANOG, as well as components of the polycomb repressive complex 2 (PRC2). Consistently, RSL24D1 is required for mouse ESC self-renewal and proliferation. Taken together, we show that RSL24D1-dependant ribosome biogenesis is required to both sustain the expression of pluripotent transcriptional programs and silence developmental programs, which concertedly dictate ESC homeostasis.

developmental biology↗

bioRxiv2020

Translation-dependent and independent mRNA decay occur through mutually exclusive pathways that are defined by ribosome density during T Cell activation.

mRNA translation and degradation are strongly interconnected processes that participate in the fine tuning of gene expression. Particularly, targeting mRNAs to translation-dependent degradation (TDD) could attenuate protein expression by making any increase in mRNA translation self-limiting. However, the extent to which TDD is a general mechanism for limiting protein expression is currently unknown. Here we describe a comprehensive analysis of basal and signal-induced TDD in mouse primary CD4 T cells. Our data indicate that most cellular transcripts are decayed to some extent in a translation-dependent manner, both in resting and activated cells. Our analysis further identifies the length of untranslated regions, the density of ribosomes and the GC content of the coding region as major determinants of TDD magnitude. Consistent with this, all transcripts that undergo changes in ribosome density upon T cell activation display a corresponding change in their TDD level. Surprisingly, the amplitude of translation-independent mRNA decay (TID) appears as a mirror image of TDD. Moreover, TID also responds to changes in ribosome density upon T cell activation but in the opposite direction from the one observed for TDD. Our data demonstrate a strong interconnection between mRNA translation and decay in mammalian cells. Furthermore, they indicate that ribosome density is a major determinant of the pathway by which transcripts are degraded within cells.

genomics↗

bioRxiv2020

Loop extrusion as a mechanism for DNA Double-Strand Breaks repair foci formation

DNA Double-Strand Breaks (DSBs) repair is essential to safeguard genome integrity. Upon DSBs, the ATM PI3K kinase rapidly triggers the establishment of megabase-sized, {gamma}H2AX-decorated chromatin domains which further act as seeds for the formation of DNA Damage Response (DDR) foci1. How these foci are rapidly assembled in order to establish a "repair-prone" environment within the nucleus is yet unclear. Topologically Associating Domains (TADs) are a key feature of 3D genome organization that regulate transcription and replication, but little is known about their contribution to DNA repair processes2,3. Here we found that TADs are functional units of the DDR, instrumental for the correct establishment of {gamma}H2AX/53BP1 chromatin domains in a manner that involves one-sided cohesin-mediated loop extrusion on both sides of the DSB. We propose a model whereby H2AX-containing nucleosomes are rapidly phosphorylated as they actively pass by DSB-anchored cohesin. Our work highlights the critical impact of chromosome conformation in the maintenance of genome integrity and provides the first example of a chromatin modification established by loop extrusion.

molecular biology↗

bioRxiv2019

Sen1 is required for RNA Polymerase III transcription termination in an R-loop independent manner.

R-loop disassembly by the human helicase Senataxin contributes to genome stability and to proper transcription termination at a subset of RNA polymerase II genes. Whether Senataxin-mediated R-loop disassembly also contributes to transcription termination at other classes of genes has remained unclear. Here we show in fission yeast that SenataxinSen1 promotes efficient termination of RNA Polymerase III (RNAP3) transcription in vivo. In the absence of SenataxinSen1, RNAP3 accumulates downstream of the primary terminator at RNAP3-transcribed genes and produces long exosome-sensitive 3-extended transcripts. Importantly, neither of these defects was affected by the removal of R-loops. The finding that SenataxinSen1 acts as an ancillary factor for RNAP3 transcription termination in vivo challenges the pre-existing view that RNAP3 terminates transcription autonomously. We propose that Senataxin is a cofactor for transcription termination that has been co-opted by different RNA polymerases in the course of evolution.

molecular biology↗

bioRxiv2018

Understanding RNP remodelling uncovers RBPs functionally required for viral replication

The compendium of RNA-binding proteins (RBPome) has been greatly expanded by the development of RNA-interactome capture (RNA-IC). However, it remains unknown how responsive is the RBPome and whether these responses are biologically relevant. To answer these questions, we created comparative RNA-IC to analyse cells challenged with an RNA virus, called sindbis (SINV). Strikingly, the virus altered the activity of 245 RBPs, many of which were newly discovered by RNA-IC. Mechanistically, alterations in RNA binding upon SINV infection are caused by changes in the subcellular localisation of RBPs and RNA availability. Moreover, RBPome responses are crucial, as perturbation of dynamic RBPs modulates the capacity of the virus to infect the cell. For example, ablation of XRN1 causes cells to be refractory to infection, while GEMIN5 moonlights as a novel antiviral factor. Therefore, RBPome remodelling provides a mechanism by which cells can extensively rewire gene expression in response to physiological cues.\n\nHIGHLIGHTSO_LIA quarter of the RBPome remodels upon SINV infection.\nC_LIO_LIThe remodelling is caused by changes in protein localisation and RNA availability.\nC_LIO_LIRewiring of the RBPome is crucial for viral infection efficacy.\nC_LIO_LIWe discover RBPs with previously unknown anti- or pro-viral activity.\nC_LI

molecular biology↗

bioRxiv2017

Efficient genome editing in primary cells and in vivo using viral-derived "Nanoblades" loaded with Cas9/sgRNA ribonucleoproteins

Programmable nucleases have enabled rapid and accessible genome engineering in eukaryotic cells and living organisms. However, their delivery into target cells can be technically challenging when working with primary cells or in vivo. Using engineered murine leukemia virus-like particles loaded with Cas9/sgRNA ribonucleoproteins (\"Nanoblades\"), we were able to induce efficient genome-editing in cell lines and primary cells including human induced pluripotent stem cells, human hematopoietic stem cells and mouse bone-marrow cells. Transgene-free Nanoblades were also capable of in vivo genome-editing in mouse embryos and in the liver of injected mice. Nanoblades can be complexed with donor DNA for \"all-in-one\" homology-directed repair or programmed with modified Cas9 variants to mediate transcriptional up-regulation of target genes. Nanoblades preparation process is simple, relatively inexpensive and can be easily implemented in any laboratory equipped for cellular biology.

cell biology↗