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O'Connell, M. A.

Publications and source records attributed to O'Connell, M. A..

5 recordsLinked to original sources
bioRxiv2025

Editing-independent effects of Adar in Drosophila melanogaster

Vertebrate ADAR RNA editing enzymes prevent cellular dsRNA from aberrantly activating antiviral dsRNA sensors. ADARs inhibit antiviral sensor activation by deaminating selected adenosines to inosines in dsRNA and by engaging in inhibitory protein interactions with sensors on dsRNA. ADARs interact with Dicers and, in the Drosophila Adar5G1 null mutant Dicer 2 acts as the antiviral dsRNA sensor mediating aberrant innate immune induction. We overexpressed active Adar isoforms or a catalytically-inactive Adar E374A protein from UAS-Adar constructs under the control of a temperature-regulated Act5Cts-GAL4 driver. Overexpression of the edited AdarG isoform or AdarEA cause larval lethality with aberrant innate immune induction. Some escaper pupae are formed with head eversion defects. AdarS overexpression is also lethal with no progeny pupae. Ecdysone signaling gene and innate immune gene expression are aberrantly elevated in the AdarG overexpressing pupae. RNAi knockdown of Ecdysone Receptor A (EcR A) or increasing expression of HP1 partially rescue AdarG overexpression defects and normalize gene expression in progeny flies, indicating that aberrant epigenetic silencing is also involved. The structure of an ADAR2 dimer on dsRNA shows the the glycine in AdarG is suitably positioned for Adar contacts with other proteins on dsRNA.

developmental biology↗
bioRxiv2025

Biosynthesis and Bioactivity of Anti-Inflammatory Triterpenoids in Calendula officinalis (pot marigold)

Plants have been central to traditional medicine for millennia, yet the precise metabolites responsible for their therapeutic properties often remain unidentified. Moreover, the low natural abundance and structural complexity of bioactive molecules can hinder their accessibility and chemical synthesis. Here, we investigate the widely reported anti-inflammatory properties of Calendula officinalis (pot marigold), an ancient medicinal herb. We confirm C16-hydroxylated triterpenoids as key contributors to the anti-inflammatory activity of C. officinalis floral extracts and uncover a novel mechanism by which they act in modulating interleukin 6 release. Through biosynthetic pathway elucidation, we demonstrate that the oxidosqualene synthase catalysing the first committed step emerged early in Asteraceae evolution and identify residues governing product specificity. Further, we functionally characterise cytochrome P450s and acyltransferases responsible for downstream modifications. By reconstructing the complete biosynthetic pathway in the heterologous plant chassis Nicotiana benthamiana, we provide a platform for production of the anti-inflammatory components. Our work highlights how integrated studies of bioactivity and biosynthesis can unlock the therapeutic potential of medicinal plants.

plant biology↗
bioRxiv2023

Aberrant activation of the innate immune sensor PKR by self dsRNA is prevented by direct interaction with ADAR1

Loss of dsRNA editing by Adar1 leads to aberrant interferon induction in Adar null mouse embryos. Adar Mavs mutants, in which this interferon induction is prevented, die within two weeks of birth. We show here that early death of pups is reduced in Adar Mavs EIF2k2 (Pkr) mutants, identifying PKR as the second aberrantly activated dsRNA sensor in Adar mutant mice. In intestines of Adar Mavs pups transit amplifying progenitor cells in intestinal crypts die and intestinal villi are lost in pups before death; intestinal defects are prevented in Adar Mavs Eifak2. In human A549 lung cancer cells ADAR1 forms a complex with PKR. AlphaFold modelling predicts a direct inhibitory interaction of ADAR1 dsRBDIII with the PKR near the kinase active site and a new mode for ADAR1 dsRNA-binding. Mutations at residues required for ADAR1 dsRNA binding or for predicted PKR contacts, prevent interaction with PKR.

immunology↗
bioRxiv2021

The mechanical regulation of RNA binding protein hnRNPC in the failing heart

Cardiac pathologies are characterized by intense remodeling of the extracellular matrix (ECM) that eventually leads to heart failure. Cardiomyocytes respond to the ensuing biomechanical stress by re-expressing fetal contractile proteins via transcriptional and post-transcriptional processes, like alternative splicing (AS). Here, we demonstrate that the heterogeneous nuclear ribonucleoprotein C (hnRNPC) is upregulated and relocates to the sarcomeric Z-disk upon ECM pathological remodeling. We show that this is an active site of localized translation, where the ribonucleoprotein associates to the translation machinery. Alterations in hnRNPC expression and localization can be mechanically determined and affect the AS of numerous mRNAs involved in mechanotransduction and cardiovascular diseases, like Hippo pathway effector YAP1. We propose that cardiac ECM remodeling serves as a switch in RNA metabolism by impacting an associated regulatory protein of the spliceosome apparatus. These findings offer new insights on the mechanism of mRNAs homeostasis mechanoregulation in pathological conditions.

pathology↗