Biology subjects

Palazzo, A. F.

Publications and source records attributed to Palazzo, A. F..

12 recordsLinked to original sources

bioRxiv2025

Transcription-induced mutation and gBGC at the Transcriptional Start Site impact the evolution of human protein-coding genes

In the human genome, mutation rates vary along genes, yet how their fine-scale structure contributes to gene evolution has remained largely unexplored. Here, we map inherited mutations at single-nucleotide resolution and uncover a striking hypermutation peak at transcription start sites (TSSs). This pattern is observed both in population polymorphisms and in de novo mutations from parent-offspring trios, and is dependent on transcriptional activity in testes. We also find similar hypermutation peaks at TSSs used to produce long noncoding RNAs and at intergenic RNA Polymerase II pause sites. In addition, we identify distinct mutational signatures at exon-intron boundaries and in introns. By comparing the current nucleotide content to predicted equilibrium levels, inferred from mutation and fixation rates, and by analyzing derived ancestral frequency spectrums, we detect signals that are compatible with a low level of ongoing background GC-biased gene conversion (gBGC) throughout the region and ancestral elevated gBGC activity downstream from the TSS. Using a forward-in-time simulation algorithm, we show that the current nucleotide composition surrounding the TSS of protein-coding genes is best explained by local mutation biases coupled to ongoing and ancestral patterns of gene conversions. Our simulations allow us to infer several features of these gBGC events. Overall, these findings indicate that the nucleotide composition around TSSs is largely shaped by non-adaptive forces, particularly mutation bias and gBGC.

evolutionary biology↗

bioRxiv2025

The genetic driver of Acute Necrotizing Encephalopathy, RANBP2, regulates the inflammatory response to Influenza A virus infection

Influenza virus infections can cause severe complications such as Acute Necrotizing Encephalopathy (ANE), which is characterised by rapid onset pathological inflammation following febrile infection. Heterozygous dominant mutations in the nucleoporin RANBP2/Nup358 predispose to influenza-triggered ANE1. The aim of our study was to determine whether RANBP2 plays a role in IAV-triggered inflammatory responses. We found that the depletion of RANBP2 in a human airway epithelial cell line increased IAV genomic replication by favouring the import of the viral polymerase subunits, PB1, PB2 and PA following viral transcription and translation. Additionally, RANBP2 knockdown enhanced the cytoplasmic export of viral RNA (vRNA) and disrupted segment stoichiometry, which associated with elevated production of the pro-inflammatory chemokines CXCL8, CXCL10, CCL2, CCL3 and CCL4 in human primary macrophages. Using CRISPR-Cas9 knock-in for the ANE1 disease variant RANBP2-T585M, we further demonstrate that this point mutation causes a loss-of-localisation phenotype that excludes RANBP2 from the nuclear envelope, which phenocopies RANBP2 knockdown by increasing IAV replication and driving pro-inflammatory cytokine expression following infection. Together, our results reveal that RANBP2 regulates influenza RNA replication and nuclear export, thereby restraining virus-induced hyperinflammation, and further suggest that ANE1 pathogenesis results from the impaired localisation of RANBP2 at the nuclear envelope.

immunology↗

bioRxiv2024

Genetic and selective constraints on the optimization of gene product diversity

RNA and protein expressed from the same gene can have diverse isoforms due to various post-transcriptional and post-translational modifications. For the vast majority of alternative isoforms, It is unknown whether they are adaptive or simply biological noise. As we cannot experimentally probe the function of each isoform, we can ask whether the distribution of isoforms across genes and across species is consistent with expectations from different evolutionary processes. However, there is currently no theoretical framework that can generate such predictions. To address this, we developed a mathematical model where isoform abundances are determined collectively by cis-acting loci, trans-acting factors, gene expression levels, and isoform decay rates to predict isoform abundance distributions across species and genes in the face of mutation, genetic drift, and selection. We found that factors beyond selection, such as effective population size and the number of cis-acting loci, significantly influence evolutionary outcomes. Notably, suboptimal phenotypes are more likely to evolve when the population is small and/or when the number of cis-loci is large. We also explored scenarios where modification processes have both beneficial and detrimental effects, revealing a non-monotonic relationship between effective population size and optimization, demonstrating how opposing selection pressures on cis- and trans-acting loci can constrain the optimization of gene product diversity. As a demonstration of the power of our theory, we compared the expected distribution of A-to-I RNA editing levels in coleoids and found this to be largely consistent with non-adaptive explanations.

evolutionary biology↗

bioRxiv2024

The GC-content at the 5'ends of human protein-coding genes is undergoing mutational decay

In vertebrates, most protein-coding genes have a peak of GC-content near their 5 transcriptional start site (TSS). This feature promotes both the efficient nuclear export and translation of mRNAs. Despite the importance of GC-content for RNA metabolism, its general features, origin, and maintenance remain mysterious. We investigated the evolutionary forces shaping GC-content at the transcriptional start site (TSS) of genes through both comparative genomic analysis of nucleotide substitution rates between different species and by examining human de novo mutations. Our data suggests that GC-peaks at TSSs were present in the last vertebrate common ancestor and are largely dictated by recombination patterns. We observe that in primates and rodents, where recombination is directed away from TSSs by PRDM9, GC-content at protein-coding gene TSSs is currently undergoing mutational decay. In canids, which lack PRDM9 and perform recombination at TSSs, GC-content at protein-coding gene TSSs is increasing. These patterns extend into the open reading frame affecting protein-coding regions, and we show that changes in GC-content due to recombination affect synonymous codon position choices at the start of the open reading frame. Our results indicate that although high GC-content in protein-coding genes may be shaped by selective pressures to enhance expression, the dynamics of GC-content in mammals are largely shaped by patterns of recombination.

genomics↗

bioRxiv2024

Cytoplasmic protein-free mRNA induces stress granules by two G3BP1/2-dependent mechanisms

Stress granules are cytoplasmic membraneless organelles that sequester proteins and non-translating mRNAs in response to various stressors. To assess the contributions of mRNA and RNA-binding proteins to stress granule formation, we use microinjection to deliver protein-free mRNA into the cytoplasm in a controlled manner. We demonstrate that mRNAs trigger stress granule formation through two mechanisms that are enhanced by the presence of G3BP1 and G3BP2. Low concentrations of in vitro transcribed mRNA activated protein kinase R (PKR), leading to phosphorylation and inhibition of the eukaryotic translation initiation factor eIF2 and stress granule formation. This was inhibited by replacing uridine with pseudouridine in the mRNA or by treating it with RNase III, which cleaves double-stranded RNA. High concentrations of mRNA triggered stress granule formation by a mechanism that was independent of PKR and enhanced by G3BP1/2, highlighting the importance of both protein-free mRNA and RNA-binding proteins in stress granule formation. Graphical Abstract/Model O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=197 SRC="FIGDIR/small/578830v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@1b1bcfeorg.highwire.dtl.DTLVardef@1eee33corg.highwire.dtl.DTLVardef@888c9forg.highwire.dtl.DTLVardef@c835aa_HPS_FORMAT_FIGEXP M_FIG C_FIG SummaryMicroinjected mRNA induces stress granules in mammalian cells by two G3BP1/2-dependent mechanisms: one requires the stress-sensing protein kinase PKR to phosphorylate the translation initiation factor eIF2, and the other is independent of PKR and phospho-eIF2 and acts when the cytoplasmic concentration of ribosome-free mRNA is increased acutely.

cell biology↗

bioRxiv2023

N-6-methyladenosine (m6A) Promotes the Nuclear Retention of mRNAs with Intact 5' Splice Site Motifs

In humans, misprocessed mRNAs containing intact 5' Splice Site (5'SS) motifs are nuclear retained and targeted for decay by ZFC3H1, a component of the Poly(A) Exosome Targeting complex, and U1-70K, a component of the U1 snRNP. In S. pombe, the ZFC3H1 homolog, Red1, binds to the YTH-domain containing protein Mmi1 to target certain RNA transcripts to nuclear foci for nuclear retention and decay. Here we show that YTHDC1 and YTHDC2, two YTH domain-containing proteins that bind to N-6-methyladenosine (m6A) modified RNAs, interact with ZFC3H1 and U1-70K, and are required for the nuclear retention of mRNAs with intact 5'SS motifs. Disruption of m6A deposition inhibits both the nuclear retention of these transcripts and their accumulation in YTHDC1-enriched foci that are adjacent to nuclear speckles. Endogenous RNAs with intact 5'SS motifs, such as intronic polyadenylated transcripts, tend to be m6A-modified at low levels. Thus, m6A modification acts in a conserved quality control mechanism that targets misprocessed mRNAs for nuclear retention and decay.

molecular biology↗

bioRxiv2021

Architecture of the cytoplasmic face of the nuclear pore

The nuclear pore complex (NPC) is the sole bidirectional gateway for nucleocytoplasmic transport. Despite recent progress in elucidating the NPC symmetric core architecture, the asymmetrically decorated cytoplasmic face, essential for mRNA export and a hotspot for nucleoporin-associated diseases, has remained elusive. Here, we report a composite structure of the entire human cytoplasmic face obtained by combining biochemical reconstitution, crystal structure determination, docking into cryo-electron tomographic reconstructions, and physiological validation, accounting for a third of the NPCs mass. Whereas an evolutionarily conserved [~]540 kDa hetero-hexameric cytoplasmic filament nucleoporin complex is anchored by species-specific motifs above the central transport channel, attachment of the pentameric NUP358 bundles depends on the double-ring arrangement of the coat nucleoporin complex. Our results and the predictive power of our composite structure provide a rich foundation for elucidating the molecular basis of mRNA export and nucleoporin diseases. One sentence summaryAn interdisciplinary analysis established the near-atomic molecular architecture of the cytoplasmic face of the human nuclear pore complex.

biochemistry↗

bioRxiv2021

ZFC3H1 and U1-70K promote the nuclear retention of mRNAs with 5' splice site motif within nuclear speckles

Quality control of mRNA represents an important regulatory mechanism for gene expression in eukaryotes. One component of this quality control is the nuclear retention and decay of misprocessed RNAs. Previously, we demonstrated that mature mRNAs containing a 5 splice site (5SS) motif, which is typically found in misprocessed RNAs such as intronic polyadenylated (IPA) transcripts, are nuclear retained and degraded. Here we demonstrate that these transcripts require the zinc finger protein ZFC3H1 for their decay and nuclear retention into nuclear speckles. Furthermore, we find that U1-70K, a component of the U1 snRNP spliceosomal complex, is also required for their nuclear retention and likely functions in the same pathway as ZFC3H1. Finally, we show that the disassembly of nuclear speckles impairs the nuclear retention of mRNAs with 5SS motifs. Together, our results suggest a model where mRNAs with 5SS motifs are recognized by U1 snRNP, which then acts with ZFC3H1 to both promote their decay and prevent nuclear export of these mRNAs by sequestering them in nuclear speckles. Our results highlight a splicing independent role of U1 snRNP and indicate that it works in conjunction with ZFC3H1 in preventing the nuclear export of misprocessed mRNAs.

molecular biology↗

bioRxiv2019

A proximity biotinylation map of a human cell

Compartmentalization is a defining characteristic of eukaryotic cells, partitioning cellular processes into discrete subcellular locations. High throughput microscopy1 and biochemical fractionation coupled with mass spectrometry2-6 have helped to define the proteomes of a variety of organelles and macromolecular structures. However, many other intracellular compartments have remained refractory to such approaches, due for example to difficulty in purifying non-membrane bound structures. Proximity-dependent biotinylation techniques such as BioID provide an alternative approach for defining the composition of cellular compartments in living cells7-10. Here we present a BioID-based map of a human cell based on 192 markers from 32 different subcellular compartments, comprising 35,902 high confidence proximity interactions, and defining the intracellular locations of 4,145 unique proteins in HEK 293 cells. Our localization predictions meet or exceed previous-approaches, with higher specificity, and enabled the discovery of proteins at the mitochondrial outer membrane-endoplasmic reticulum (ER) interface that are critical for mitochondrial homeostasis. Based on this dataset, we have established humancellmap.org as a community resource that provides online tools for localization analysis of user BioID data, and demonstrate how this resource can be used to better understand BioID datasets.

molecular biology↗

bioRxiv2019

TPR is required for the nuclear export of mRNAs and lncRNAs from intronless and intron-poor genes

While splicing has been shown to enhance nuclear export, it has remained unclear whether mRNAs generated from intronless genes use specific machinery to promote their export. Here we investigate the role of the major nuclear pore basket protein, TPR, in regulating mRNA and lncRNA nuclear export in human cells. By sequencing mRNA from the nucleus and cytosol of control and TPR-depleted cells, we provide evidence that TPR is required for the nuclear export of mRNAs and lncRNAs that are generated from intronless and intron-poor genes, and we validate this with reporter constructs. Moreover, in TPR-depleted cells reporter mRNAs generated from intronless genes accumulate in nuclear speckles and are bound to Nxf1. These observations suggest that TPR acts downstream of Nxf1 recruitment, and may allow mRNAs to leave nuclear speckles and properly dock with the nuclear pore. In summary, our study provides one of the first examples of a factor that is required for the nuclear export of intronless and intron-poor mRNAs and lncRNAs.

molecular biology↗

bioRxiv2019

Pyruvate Kinase M Links Glucose Availability to Protein Synthesis

How human cells coordinate various metabolic processes, such as glycolysis and protein translation, remains unclear. One key insight is that various metabolic enzymes have been found to associate with mRNAs, however whether these enzymes regulate mRNA biology in response to changes in cellular metabolic state remains unknown. Here we report that the glycolytic enzyme, pyruvate kinase M (PKM), inhibits the translation of 7% of the transcriptome in response to elevated levels of glucose and pyruvate. Our data suggest that in the presence of glucose and pyruvate, PKM associates with ribosomes that are synthesizing stretches of polyacidic nascent polypeptides and stalls the elongation step of translation. PKM-regulated mRNAs encode proteins required for the cell cycle and may explain previous results linking PKM to cell cycle regulation. Our study uncovers an unappreciated link between glycolysis and the ribosome that likely coordinates the intake of glycolytic metabolites with the regulation of protein synthesis and the cell cycle.

molecular biology↗

bioRxiv2019

RanBP2/Nup358 enhances RNAi activity by sumoylating and stabilizing Argonaute 1

RanBP2/Nup358 is one of the main components of the cytoplasmic filaments of the nuclear pore complex. It has been speculated that RanBP2, which has an E3 SUMO-ligase domain, may alter the composition of messenger ribonucleoprotein (mRNP) complexes as they emerge from the nuclear pore and thus regulate the ultimate fate of the mRNA in the cytoplasm. Four separate missense mutations in RanBP2 cause Acute Necrotizing Encephalopathy 1 (ANE1), which manifests as a sharp rise in cytokine production after common viral infections such as influenza and parainfluenza. However, how RanBP2 and its ANE1-associated mutations affect cytokine production is not well understood. Here we report that RanBP2 represses the translation of the interleukin-6 (IL6) mRNA, which encodes a cytokine that is aberrantly up-regulated in ANE1. Our data indicates that soon after its production, the IL6 mRNP recruits the RNA-induced silencing complex (RISC) bound to Let7 miRNA. After this mRNP is exported, RanBP2 sumoylates the RISC-component AGO1, thereby stabilizing it and enforcing mRNA silencing. Collectively, these results support a model whereby RanBP2 promotes an mRNP remodelling event that is critical for the miRNA-mediated suppression of clinically relevant mRNAs, such as IL6.

molecular biology↗