Project description:Protein truncating variants caused by stop codons are the most prevalent class of rare variant mutations in neurodevelopmental diseases, with UGA codons being most common. Suppressor transfer RNA (sup-tRNA) have therapeutic potential for premature termination codon (PTC) rescue, but have thus far underperformed by traditional AAV delivery platforms and progress has been hampered by the lack of methods to non-invasively assess in vivo activity in mammalian brain. To fill this material gap, we utilize transcranial in vivo bioluminescence imaging data from a luciferase-UGA mouse model to optimize viral payloads with sup-tRNA genes. These data demonstrate that U6 promoter-driven and single-stranded AAV2/9 constructs show variable and dose-dependent activity, whereas self-complementary AAV2/9 with the tRNA in a minimal 100bp genomic context provides broad and efficacious PTC rescue. Further, payload tRNA multiplexing and use of tRNA introns enable efficacy of low viral titers and sustained rescue. tRNA sequencing of scAAV delivered ArgUGA sup-tRNA in brain demonstrate no effects on endogenous tRNA levels, their acylation or processing, and these features are also maintained in scAAV delivered ArgUGA sup-tRNA. Collectively, this work defines a scalable strategy for precision UGA PTC stop codon suppression, supporting development of durable genetic rescue therapies for neurodevelopmental disorders in the mammalian brain.
Project description:SECIS binding protein 2 (SECISBP2) increases the efficiency of recoding of UGA codons as selenocysteine (Sec) during translation of mRNAs containing a selenocysteine insertion sequence (SECIS) in the 3’-untranslated region. Using ribosomal profiling, we have previously studied selenoprotein translation in hepatocyte-specific Secisbp2-deficient mouse liver and neuron-specific Secisbp2-mutant mouse brain. The use of organs carries the limitation of cellular heterogeneity with cells still expressing wild-type SECISBP2 that might potentially confound analyses and conclusions. To address this concern, we studied a haploid human HAP1 cell line carrying a non-functional SECISBP2 protein. These cells are still capable of metabolically incorporating 75Se into selenoproteins. We performed ribosomal profiling, and show that the efficiency of UGA recoding is gene-specific in SECISBP2- deficient cells. Analysis of ribosomes with UGA either at the A-site or the P-site revealed in a transcript-specific manner that SECISBP2 helps to recruit tRNASec and stabilizes mRNA. We propose a new measure to assess UGA/Sec read-through at codon resolution in all selenoproteins, i.e. the proportion of ribosomes carrying UGA in the P-site, pUGA. An additional, new observation is frame- shifting occurring after the UGA/Sec codon in GPX1, SELENOF, and SELENOW in HAP1 cells, a finding corroborated by reanalysis of neuron-specific Secisbp2-mutant brains.
Project description:Mice carrying genomic deletions of SECIS1 or SECIS2 in the Selenop gene were euthanized and liver tissue was harvested and processed for RNA-Seq and ribosome profiling. From these studies, we determined the affect of SECIS1 and SECIS2 on UGA redifinition across the Selenop gene.