Alessio Colantoni’s research while affiliated with Istituto Italiano di Tecnologia and other places

While it is accepted that Extracellular Vesicles (EVs)-mediated transfer of microRNAs contributes to intercellular communication, the knowledge about molecular mechanisms controlling the selective and dynamic miRNA-loading in EVs is still limited to few specific RNA-binding proteins interacting with sequence determinants. Moreover, although mutagenesis analysis demonstrated the presence/function of specific intracellular retention motifs, the interacting protein/s remained unknown. Here, PCBP2 was identified as a direct interactor of an intracellular retention motif: RIP coupled to RNA pull down and proteomic analysis demonstrated that it binds to miRNAs embedding this motif and mutagenesis proved the binding specificity. Notably, PCBP2 binding requires SYNCRIP, a previously characterized miRNA EV-loader as indicated by SYNCRIP knock-down. SYNCRIP and PCBP2 may contemporarily bind to miRNAs as demonstrated by EMSA assays and PCBP2 knock-down causes EV-loading of intracellular microRNAs. This evidence highlights that multiple proteins/miRNA interactions govern miRNA compartmentalization and identifies PCBP2 as a dominant inhibitor of SYNCRIP function.

Defects at the neuromuscular junction (NMJ) are among the earliest hallmarks of amyotrophic lateral sclerosis (ALS). According to the “dying-back” hypothesis, NMJ disruption not only precedes but also triggers the subsequent degeneration of motoneurons in both sporadic (sALS) and familial (fALS) ALS. Using human induced pluripotent stem cells (iPSCs), we show that the RNA-binding protein HuD (ELAVL4) contributes to NMJ defects and apoptosis in FUS-ALS. HuD overexpression mimics the severe FUSP525L mutation, while its knockdown rescues the FUSP525L phenotypes. In Drosophila, neuronal overexpression of the HuD ortholog, elav, induces motor dysfunction, and its knockdown improves motor function in a FUS-ALS model. Finally, we report increased HuD levels upon oxidative stress in human motoneurons and in sALS patients with an oxidative stress signature. Based on these findings, we propose that HuD plays a role downstream of FUS mutations in fALS and in sALS related to oxidative stress.

Background The Pharyngeal Endoderm (PE) is an extremely relevant developmental tissue, serving as the progenitor for the esophagus, parathyroids, thyroids, lungs, and thymus. While several studies have highlighted the importance of PE cells, a detailed transcriptional and epigenetic characterization of this important developmental stage is still missing, especially in humans, due to technical and ethical constraints pertaining to its early formation. Results Here we fill this knowledge gap by developing an in vitro protocol for the derivation of PE-like cells from human Embryonic Stem Cells (hESCs) and by providing an integrated multi-omics characterization. Our PE-like cells robustly express PE markers and are transcriptionally homogenous and similar to in vivo mouse PE cells. In addition, we define their epigenetic landscape and dynamic changes in response to Retinoic Acid by combining ATAC-Seq and ChIP-Seq of histone modifications. The integration of multiple high-throughput datasets leads to the identification of new putative regulatory regions and to the inference of a Retinoic Acid-centered transcription factor network orchestrating the development of PE-like cells. Conclusions By combining hESCs differentiation with computational genomics, our work reveals the epigenetic dynamics that occur during human PE differentiation, providing a solid resource and foundation for research focused on the development of PE derivatives and the modeling of their developmental defects in genetic syndromes.

Genome integrity is safeguarded by the DNA damage response (DDR). Controlled transcriptional dampening of genes surrounding DNA double-strand breaks (DSBs) has been shown to facilitate DNA repair. This phenomenon, defined as DSB-induced silencing in cis (DISC), involves the DDR apical kinase ATM and the Polycomb Repressive Complex 1 (PRC1). Conversely, DSBs have also been reported to induce de novo transcription of damaged-induced long non-coding RNAs (dilncRNAs) in a MRE11-RAD50-NBS1 (MNR) complex-dependent manner. MRN also controls the recruitment to DSB of the ribonuclease DROSHA, which together with DICER, stimulates DDR signaling and DNA repair. Here, we reconcile these apparently contrasting observations by showing that dilncRNA, together with DROSHA and DICER, but not GW182-like proteins required for miRNA-mediated gene silencing, controls DISC. Indeed, similarly to ATM, MRN inhibition abolishes DISC while pharmacological enhancement of DICER ribonuclease activity by Enoxacin improves DISC. Importantly, Enoxacin administration restores DISC upon ATM inhibition, demonstrating that DICER promotes DISC independently from ATM. Differently, Enoxacin does not restore DISC upon MRN inhibition, suggesting that DICER acts downstream to dilncRNA biogenesis and DROSHA recruitment. Mechanistically, we show that DROSHA and DICER control the recruitment of the PRC1 component BMI1 at DSBs and the consequent H2A-K119 ubiquitination. Upon DSBs formation, BMI1 and DROSHA interact in an RNA-dependent manner. Indeed, BMI1 associates to dilncRNA and do so in a DROSHA- and DICER-dependent manner. Importantly, inhibition of dilncRNA function by antisense oligonucleotides or Cas13-mediated targeting is sufficient to reduce BMI1 recruitment and DISC at individual loci. We propose that dilncRNAs together with DROSHA and DICER control DISC at genomic DSB by supporting PRC1 recruitment and chromatin ubiquitination.

The combination of morphogenetic and transcription factors together with the synergic aid of noncoding RNAs and their cognate RNA binding proteins contribute to shape motor neurons (MN) identity. Here, we extend the noncoding perspective of human MN, by detailing the molecular and biological activity of CyCoNP (as Cytoplasmic Coordinator of Neural Progenitors) a highly expressed and MN-enriched human lncRNA. Through in silico prediction, in vivo RNA purification and loss of function experiments followed by RNA-sequencing, we found that CyCoNP sustains a specific neuron differentiation program, required for the physiology of both neuroblastoma cells and hiPSC-derived MN, which mainly involves miR-4492 and NCAM1 mRNA. We propose a novel lncRNA-mediated ‘dual mode’ of action, in which CyCoNP acts in trans as a classical RNA sponge by sequestering miR-4492 from its pro-neuronal targets, including NCAM1 mRNA, and at the same time it plays an additional role in cis by interacting with NCAM1 mRNA and regulating the availability and localization of the miR-4492 in its proximity. These data highlight novel insights into the noncoding RNA-mediated control of human neuron physiology and point out the importance of lncRNA-mediated interactions for the spatial distribution of regulatory molecules.

Epitranscriptomics represents a further layer of gene expression regulation. Specifically, N6-methyladenosine (m6A) regulates RNA maturation, stability, degradation, and translation. Regarding microRNAs (miRNAs), while it has been reported that m6A impacts their biogenesis, the functional effects on mature miRNAs remain unclear. Here, we show that m6A modification on specific miRNAs weakens their coupling to AGO2, impairs their function on target mRNAs, determines their delivery into extracellular vesicles (EVs), and provides functional information to receiving cells. Mechanistically, the intracellular functional impairment is caused by m6A-mediated inhibition of AGO2/miRNA interaction, the EV loading is favored by m6A-mediated recognition by the RNA-binding protein (RBP) hnRNPA2B1, and the EV-miRNA function in the receiving cell requires their FTO-mediated demethylation. Consequently, cells express specific miRNAs that do not impact endogenous transcripts but provide regulatory information for cell-to-cell communication. This highlights that a further level of complexity should be considered when relating cellular dynamics to specific miRNAs.

Proteins are crucial in regulating every aspect of RNA life, yet understanding their interactions with coding and noncoding RNAs remains limited. Experimental studies are typically restricted to a small number of cell lines and a limited set of RNA-binding proteins (RBPs). Although computational methods based on physico-chemical principles can predict protein-RNA interactions accurately, they often lack the ability to consider cell-type-specific gene expression and the broader context of gene regulatory networks (GRNs). Here, we assess the performance of several GRN inference algorithms in predicting protein-RNA interactions from single-cell transcriptomic data, and propose a pipeline, called scRAPID (single-cell transcriptomic-based RnA Protein Interaction Detection), that integrates these methods with the catRAPID algorithm, which can identify direct physical interactions between RBPs and RNA molecules. Our approach demonstrates that RBP–RNA interactions can be predicted from single-cell transcriptomic data, with performances comparable or superior to those achieved for the well-established task of inferring transcription factor–target interactions. The incorporation of catRAPID significantly enhances the accuracy of identifying interactions, particularly with long noncoding RNAs, and enables the identification of hub RBPs and RNAs. Additionally, we show that interactions between RBPs can be detected based on their inferred RNA targets. The software is freely available at https://github.com/tartaglialabIIT/scRAPID.

Pathogenic variants in the GNAO1 gene, encoding the alpha subunit of an inhibitory heterotrimeric guanine nucleotide-binding protein (Go) highly expressed in the mammalian brain, have been linked to encephalopathy characterized by different combinations of neurological symptoms, including developmental delay, hypotonia, epilepsy and hyperkinetic movement disorder with life-threatening paroxysmal exacerbations. Currently, there are only symptomatic treatments, and little is known about the pathophysiology of GNAO1-related disorders. Here, we report the characterization of a new in vitro model system based on patient-derived induced pluripotent stem cells (hiPSCs) carrying the recurrent p.G203R amino acid substitution in Gαo, and a CRISPR-Cas9-genetically corrected isogenic control line. RNA-Seq analysis highlighted aberrant cell fate commitment in neuronal progenitor cells carrying the p.G203R pathogenic variant. Upon differentiation into cortical neurons, patients’ cells showed reduced expression of early neural genes and increased expression of astrocyte markers, as well as premature and defective differentiation processes leading to aberrant formation of neuronal rosettes. Of note, comparable defects in gene expression and in the morphology of neural rosettes were observed in hiPSCs from an unrelated individual harboring the same GNAO1 variant. Functional characterization showed lower basal intracellular free calcium concentration ([Ca²⁺]i), reduced frequency of spontaneous activity, and a smaller response to several neurotransmitters in 40- and 50-days differentiated p.G203R neurons compared to control cells. These findings suggest that the GNAO1 pathogenic variant causes a neurodevelopmental phenotype characterized by aberrant differentiation of both neuronal and glial populations leading to a significant alteration of neuronal communication and signal transduction.

Early defects at the neuromuscular junction (NMJ) are among the first hallmarks of the progressive neurodegenerative disease amyotrophic lateral sclerosis (ALS). According to the "dying back" hypothesis, disruption of the NMJ not only precedes, but is also a trigger for the subsequent degeneration of the motoneuron. However, the pathogenic mechanisms linking genetic and environmental factors to NMJ defects remain elusive. Here we show that increased expression of the neural RNA binding protein HuD (ELAVL4) at the presynaptic level is sufficient to cause NMJ defects and trigger apoptosis in co-cultures of motoneurons and skeletal muscle derived from human induced pluripotent stem cells (iPSCs). These phenotypes are strikingly similar to those caused by the severe FUS P525L variant. Moreover, HuD knock-down in motoneurons reverts the adverse effects of the FUS P525L mutation in iPSC-derived co-cultures. These findings were validated in vivo by taking advantage of a Drosophila model, where neuronal-restricted overexpression of the HuD-related gene, elav , exacerbates the effects of FUS expression and produces per se a motor phenotype. Notably, in this fly model, neuronal-restricted elav knockdown significantly rescues motor dysfunction caused by FUS. Finally, we show that HuD levels are increased upon oxidative stress in human motoneurons, and in sporadic ALS patients with a signature related to oxidative stress. On these bases, we propose HuD as a key protein involved in causing early pathogenic alterations and offers a potential new therapeutic target for early intervention aimed at the NMJ in ALS.