Biology subjects

Scacchetti, A.

Publications and source records attributed to Scacchetti, A..

8 recordsLinked to original sources

bioRxiv2025

Pseudouridine selects RNAs for extracellular transport

RNAs move through the extracellular space to transmit information between cells, including mammalian neurons, yet how specific RNAs are channeled into these extracellular routes is unknown. Using genome-wide CRISPR screening, proteomics, and high-sensitivity transcriptomics in a neuronal model system, we identify domesticated retroviral proteins and RNA-modifying enzymes that regulate RNA loading into and transportation via extracellular vesicles. We show that the pseudouridine synthase PUS1 is a key determinant of RNA trafficking, and that its catalytic product in RNA, pseudouridine, is enriched in extracellular RNAs from transformed and primary neurons. Furthermore, the presence of pseudouridine on select RNAs is both necessary and sufficient for their extracellular export. Finally, we show that myosin light chain 6 (MYL6) is a pseudouridine-binding protein required for secretion of synthetic and endogenous RNAs. These findings reveal a biochemical code linking chemical RNA modification to extracellular transport, and establish a framework to study the function of extracellular RNAs in the nervous system and beyond.

molecular biology↗

bioRxiv2025

The Tip60 acetylome is a hallmark of the proliferative state in Drosophila

The acetyltransferase KAT5/Tip60 is an epigenetic regulator of transcription and the DNA damage response. In Drosophila, Tip60 acetylates histones as part of the DOM-A complex, but it is unclear whether it has other substrates. In this work, we comprehensively studied the functions of Tip60 in a Drosophila proliferative cell model. Depletion of Tip60 arrests the cell cycle, but remaining viable cells resist mutagenic irradiation. The impaired proliferation is explained by reduced expression of critical cell cycle genes. Tip60 binds their transcription start sites and Tip60-dependent acetylation of the histone variant H2A.V correlates with transcription activity. A potentially synergistic pathway for cell cycle regulation involves the acetylation of proteins other than histones. The Tip60-dependent nuclear acetylome contains hundreds of proteins, many of which are involved in diverse aspects of cell growth and division, including replication, mitosis, gene expression, chromatin organization and ribosome biogenesis. We hypothesize that Tip60 coordinates the proliferative state through histone and non-histone effectors. Reversible acetylation of diverse effector proteins bears potential for fine-tuning energy-intensive processes in response to stresses or nutritional shortcomings. Our study portrays the DOM-A/TIP60 complex as a general promoter of cell proliferation.

molecular biology↗

bioRxiv2023

ISWI catalyzes nucleosome sliding in condensed nucleosome arrays

How chromatin enzymes work in condensed chromatin and how they maintain diffusional mobility inside remains unexplored. We investigated these challenges using the Drosophila ISWI remodeling ATPase, which slides nucleosomes along DNA. Folding of chromatin fibers did not affect sliding in vitro. Catalytic rates were also comparable in- and outside of chromatin condensates. ISWI cross-links and thereby stiffens condensates, except when ATP hydrolysis is possible. Active hydrolysis is also required for ISWIs mobility in condensates. Energy from ATP hydrolysis therefore fuels ISWIs diffusion through chromatin and prevents ISWI from cross-linking chromatin. Molecular dynamics simulations of a monkey-bar model in which ISWI grabs onto neighboring nucleosomes, then withdraws from one before rebinding another in an ATP hydrolysis-dependent manner qualitatively agree with our data. We speculate that monkey-bar mechanisms could be shared with other chromatin factors and that changes in chromatin dynamics caused by mutations in remodelers could contribute to pathologies.

biochemistry↗

bioRxiv2023

A ligation-independent sequencing method reveals tRNA-derived RNAs with blocked 3' termini

Despite the numerous sequencing methods available, the vast diversity in size and chemical modifications of RNA molecules makes the capture of the full spectrum of cellular RNAs a difficult task. By combining quasirandom hexamer priming with a custom template switching strategy, we developed a method to construct sequencing libraries from RNA molecules of any length and with any type of 3 terminal modification, allowing the sequencing and analysis of virtually all RNA species. Ligation-independent detection of all types of RNA (LIDAR) is a simple, effective tool to comprehensively characterize changes in small non-coding RNAs and mRNAs simultaneously, with performance comparable to separate dedicated methods. With LIDAR, we comprehensively characterized the coding and non- coding transcriptome of mouse embryonic stem cells, neural progenitor cells, and sperm. LIDAR detected a much larger variety of tRNA-derived RNAs (tDRs) compared to traditional ligation-dependent sequencing methods, and uncovered the presence of tDRs with blocked 3 ends that had previously escaped detection. Our findings highlight the potential of LIDAR to systematically detect all RNAs in a sample and uncover new RNA species with potential regulatory functions.

genomics↗

bioRxiv2022

Expanding the epitranscriptomic RNA sequencing and modification mapping mass spectrometry toolbox with field asymmetric waveform ion mobility and electrochemical elution liquid chromatography

Post-transcriptional modifications of RNA strongly influence RNA structure and function. Recent advances in RNA sequencing and mass spectrometry (MS) methods have identified over 140 of these modifications on a wide variety of RNA species. Most next-generation sequencing approaches can only map one RNA modification at a time, and while MS can assign multiple modifications simultaneously in an unbiased manner, MS cannot accurately catalog and assign RNA modifications in complex biological samples due to limitations in fragment length and coverage depth. Thus, a facile method to identify novel RNA modifications while simultaneously locating them in the context of their RNA sequences is still lacking. We combined two orthogonal modes of RNA ion separation before mass-spectrometry identification: high-field asymmetric ion mobility separation (FAIMS) and electrochemically modulated liquid chromatography (EMLC). FAIMS RNA-MS increases both coverage and throughput, while the EMLC LC-MS orthogonally separates RNA of different length and charge. The combination of the two methods offers a broadly applicable platform to improve length and depth of MS-based RNA sequencing while providing contextual access to the analysis of RNA modifications.

biochemistry↗

bioRxiv2022

Permethylation of ribonucleosides provides enhanced mass spectrometry quantification of post-transcriptional modifications

Chemical modifications of RNA are associated with fundamental biological processes such as RNA splicing, export, translation, degradation, as well as human disease states such as cancer. However, the analysis of ribonucleoside modifications is impeded due to the hydrophilicity of the ribonucleoside molecules. In this research, we used solid-phase permethylation to derivatize the ribonucleosides, and the permethylated ribonucleosides, which were then quantitively analyzed using a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based method. The solid-phase permethylation efficiently derivatized the ribonucleosides, and more than 60 RNA modifications were simultaneously monitored using ultrahigh-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UHPLC-QqQ-MS) performed in the dynamic multiple reaction monitoring (dMRM) mode. Because of the increased hydrophobicity of permethylated ribonucleosides, this method enhanced retention, separation, and ionization efficiency, resulting in improved detection and quantification when compared to existing analytical strategies of RNA modifications. We applied this new approach to measure the extent of cytosine methylation and hydroxymethylation in RNA obtained from mouse embryonic stem cells with genetic deficiencies in ten-eleven translocation (TET) enzymes. The results matched previously performed analyses and highlighted the sensitivity, efficacy, and robustness of the new method. The advantage of this method enables comprehensive analysis of RNA modifications in biological samples. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=77 SRC="FIGDIR/small/477959v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@a16649org.highwire.dtl.DTLVardef@424b26org.highwire.dtl.DTLVardef@53d701org.highwire.dtl.DTLVardef@48a9cd_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2020

Drosophila SWR1 and NuA4 complexes are defined by DOMINO isoforms

Histone acetylation and deposition of H2A.Z variant are integral aspects of active transcription. In Drosophila, the single DOMINO chromatin regulator complex is thought to combine both activities via an unknown mechanism. Here we show that alternative isoforms of the DOMINO nucleosome remodeling ATPase, DOM-A and DOM-B, directly specify two distinct multi-subunit complexes. Both complexes are necessary for transcriptional regulation but through different mechanisms. The DOM-B complex incorporates H2A.V (the fly ortholog of H2A.Z) genome-wide in an ATP-dependent manner, like the yeast SWR1 complex. The DOM-A complex, instead, functions as an ATP-independent histone acetyltransferase complex similar to the yeast NuA4, targeting lysine 12 of histone H4. Our work provides an instructive example of how different evolutionary strategies lead to similar functional separation. In yeast and humans, nucleosome remodeling and histone acetyltransferase complexes originate from gene duplication and paralog specification. Drosophila generates the same diversity by alternative splicing of a single gene. HighlightsO_LIIsoforms of DOMINO dictate the formation of distinct complexes C_LIO_LIDOM-B complex is the Drosophila SWR1 and incorporates H2A.V genome-wide C_LIO_LIDOM-A complex acetylates H4K12 and is the Drosophila NuA4 C_LI

molecular biology↗

bioRxiv2017

CHRAC/ACF Contribute to the Repressive Ground State of Chromatin

The chromatin remodeling complexes CHRAC and ACF combine the ATPase ISWI with the signature subunit ACF1. These enzymes catalyze well-studied nucleosome sliding reactions in vitro, but how their actions affect physiological gene expression is unclear. Here we explored the influence of Drosophila CHRAC/ACF on transcription by complementary gain- and loss-of-function approaches.\n\nTargeting ACF1 to multiple reporter genes inserted at many different genomic locations revealed a context-dependent inactivation of poorly transcribed reporters in repressive chromatin. Accordingly, single-embryo transcriptome analysis of a Acf knock-out allele showed that only lowly expressed genes are de-repressed in the absence of ACF1. Finally, the nucleosome arrays in Acf-deficient chromatin show loss of physiological regularity, particularly in transcriptionally inactive domains.\n\nTaken together our results highlight that ACF1-containing remodeling factors contribute to the establishment of an inactive ground state of the genome through chromatin organization.

molecular biology↗