Non-(protein-)coding RNAs (ncRNAs) are broadly classified according to their length as long noncoding RNAs (lncRNAs; >150-200 nucleotides (nt)) and short ncRNAs (<150-200 nt) (Wright and Bruford, 2011). Between 4 and 10% of lncRNAs are processed to shorter RNAs (Kapranov et al, 2007; Derrien et al, 2012). Major classes of short ncRNAs include (1) endogenous microRNAs (miRNAs; approximately 19-25 nt) that are first produced as double-stranded ‘miRNA duplex’ (in which form they may also be used as therapeutic agents), whereas mature miRNAs are single-stranded and associated with RNA-induced silencing complexes (Kim, 2005; Winter et al, 2009); (2) endogenous Piwi-interacting RNA (piRNA; single-stranded, 24-31 nt; Piwi: P-element induced wimpy testis in Drosophila) that are involved in long-term transgenerational messenger RNA (mRNA) suppression in reproductive organs; (3) endogenous or synthetically produced short interfering RNAs (siRNAs; double-stranded, 20-24 nt) that induce degradation of transposable elements or mRNA targets, the latter being used as research tools in mammals (Watanabe et al, 2006, 2008; Arrigo and Pulliero, 2015; Wright and Bruford, 2011). Since knowledge on the existence and functionalities of different forms of ncRNAs is evolving rapidly, this classification of different forms of ncRNA is most likely not yet definite. Further classes of short ncRNAs are known and continue to be discovered, e.g. small nuclear RNA, small nucleolar RNA, vault RNA, or Y RNA (Martens-Uzunova et al, 2013; Kowalski and Krude, 2015).
Generally, endogenous ncRNAs have been found to be involved in post-transcriptional gene silencing, epigenetic regulation and mediation of physical and chemical environmental signals. However, although knowledge on how substances may influence the functionality of ncRNAs is growing, the potential role of ncRNAs in regulatory toxicology and the risk assessment (RA) of such substances is unclear. (Throughout this report, the term ‘substance’ is used as defined in Regulation (EC) No 1907/2006 on the Registration, Authorisation, Evaluation and Restriction of Substances (REACH), i.e. a chemical element and its compounds in the natural state or obtained by any manufacturing process, including, as applicable, necessary stabilising additives and impurities deriving from the given production process.)
As Alan Poole, Secretary General of the European Centre for the Ecotoxicology and Toxicology of Chemicals (ECETOC, Belgium), outlined in his welcome to the workshop participants, ECETOC aims at generating knowledge that regulators can use for action. In pursuing this goal, ECETOC collaborates closely with the European Chemical Industry Council Long-range Research Initiative (Cefic LRI) that funds research to generate science-based knowledge that may be used to assess and ensure the safety of substances. The ECETOC workshop ncRNAs and risk assessment science aimed at reaching a common understanding on the state-of-the-art research on ncRNAs, on the implications of ncRNA expression profile changes for the evolvement of apical effects, i.e. the observable outcomes of substance exposure to test animals (OECD, 2012), and the current and potential future role of ncRNAs in regulatory toxicology and RA. The deliverables of this workshop were not only to prepare a report that would be further processed into a manuscript to be submitted to a peer-reviewed open-access journal, but also to outline proposals for Cefic LRI-funded research to be put forward for funding in 2016 and, possibly, proposals for research to be suggested for public funding, e.g. under the European Commission programme for research and innovation Horizon 2020.