Functional analyses of brain-specific box C/D small RNAs – neuroSNORD

neuroSNORD is a multi-disciplinary project that concerns two brain-specific box C/D small nucleolar RNAs (SNORDs), namely SNORD115 and SNORD116 whose tandemly-repeated genes are subject to genomic imprinting (only the paternally-inherited allele is competent for transcription). Through an antisense-mediated mechanism, most SNORDs direct site-specific 2’-O-methylations of ribosomal, spliceosomal and transfer RNAs. As such, SNORDs are key players of epitranscriptomic gene regulation. Despite the intense research over the past 20 years, the biological and evolutionary relevance of SNORD116 and SNORD115 remain however elusive. In other words, we do not know formally their precise mode of action and cellular target RNAs in vivo. The most parsimonious hypothesis posits that such peculiar epigenetically-regulated SNORD genes, only found in placental mammals, may have shaped brain function and evolution, very likely by targeting brain-specific transcripts, possibly including mRNAs, for 2’-O-methylation. Deciphering the molecular roles of SNORD116 and SNORD115 is therefore essential, not only to unveil novel, unsuspected SNORD-mediated regulation in neurological pathways, but also because the loss of SNORD116, and possibly also of SNORD115, has been connected to the pathophysiology of Prader-Willi syndrome. The most salient phenotype of this rare human disorder is failure-to-thrive at birth followed by a true obsession for food and eating in childhood that leads to morbid obesity if left uncontrolled. Other common symptoms include sleep disturbance and altered cognitive functions including poor mental flexibility. Based on solid unpublished observations and motivated by an attractive and well-balanced combination of hypothesis-driven and exploratory research, the originality of neuroSNORD resides in its assumed wish to conduct experiments in biologically relevant (neuronal) settings, from molecules to organisms through neuronal networks. More precisely, neuroSNORD aims at unravelling how SNORD115 and/or SNORD116 regulate gene networks and, in so doing, influence adaptation to extra-uterine life, excitability of neuronal circuits and behavior. To address these appealing questions, we will combine reverse genetic approaches using a unique set of knock-out (KO) models (SNORD115-, SNORD116- and SNORD116/115-KO mice and human SNORD116-deficient cells) and innovative, deep sequencing-based methods dedicated to characterize the cellular RNA interactomes of SNORD115 and SNORD116 as well as to define the transcriptome-wide landscape of 2’-O-ribose methylated nucleotides in the brain. These molecular analyses will be accompanied by in vivo electrophysiological recordings of neuronal activities as well as a batterie of behavioral paradigms with particular focus on sleep architecture (sleep-wake cycles) and cognitive flexibility (ability to switch a learnt rule). This ambitious research program will be achieved by two groups with internationally-recognized and long-lasting expertise in the study of regulatory noncoding RNAs: J. CAVAILLE and T. KISS at the Centre de Biologie intégrative (CBI-CNRS) de Toulouse. Both partners have complementary expertise (i.e., molecular vs physiological analyses) and share the same philosophy in their desire to deepen our knowledge of the biology of SNORDs. neuroSNORD will also benefit daily from ongoing fruitful collaborative works with neurobiologists at CBI providing additional technical and conceptual expertise in the functioning of hypothalamic and monoaminergic neurons. In sum, neuroSNORD is at the interface of two fertile scientific topics in molecular biology: antisense RNA-mediated gene regulation and epitranscriptomics and we do believe that our joint effort guarantees the theoretical and practical knowledge, the scientific synergy and competitivity required to successfully accomplish the proposed neuroSNORD program.