Talk abstracts
Talk on Friday 01:30-01:45pm submitted by Lucia Johnson
Translational control of a unique bicistronic gene linked to Prader-Willi syndrome
Lucia Johnson (Biological Sciences, Carnegie Mellon University), Gemma May (Biological Sciences, Carnegie Mellon University), Robert D Nicholls (Pediatrics, University of Pittsburgh Medical Center), Joel McManus (Biological Sciences, Carnegie Mellon University)
Abstract:
Over the last decade, research has revealed a surprising array of functional microproteins encoded in small open reading frames (sORFs) upstream of previously annotated genes. These intriguing microproteins raise numerous questions about not only their biological functions, but also how separate proteins are expressed from the same (bicistronic) transcripts. The earliest identified sORF, SmN Upstream Reading Frame (SNURF), is located upstream of the human spliceosomal snRNP protein, SmN (SNRPN). Both SNURF and SNRPN are deleted in most patients with Prader-Willi syndrome, suggesting these genes may function in neuronal development and endocrine regulation. Despite being discovered over two decades ago, little is known about the translational control of SNURF-SNRPN. Most eukaryotic translation initiation occurs by 5’ to 3’ scanning by the ribosomal preinitiation complex. Thus, it is expected that translation of SNURF would prevent the translation of SNRPN. Yet, both proteins are expressed in neurons, suggesting alternative mechanisms may control SNRPN translation. We investigated SNURF-SNRPN translation using luciferase RNA reporters and found no evidence of an Internal Ribosome Entry Site (IRES) driving SNRPN translation. We instead discovered a small, deeply conserved upstream ORF (uORF) upstream of SNURF enhances SNRPN translation via delayed reinitiation. During thapsigargin induced endoplasmic reticulum stress, SNRPN translation typically increased independent of the uORF, which could reflect preinitiation complex scanning without a ternary complex. We also investigated translation of a unique SNURF-SNRPN patient allele that creates two additional uORFs upstream of SNURF. We found that this allele causes aberrant SNURF-SNRPN translation, solidifying the importance of correct SNURF-SNRPN translation in typical development. These results show that directional scanning, rather than IRES activity, ensures translation of both ORFs in a human bicistronic gene.
References:
Mohsen JJ, Martel AA, Slavoff SA. Microproteins-Discovery, structure, and function. Proteomics. 2023;23: e2100211.
Gray TA, Saitoh S, Nicholls RD. An imprinted, mammalian bicistronic transcript encodes two independent proteins. Proc Natl Acad Sci U S A. 1999;96: 5616–5621.
Harnett D, Ambrozkiewicz MC, Zinnall U, Rusanova A, Borisova E, Drescher AN, et al. A critical period of translational control during brain development at codon resolution. Nat Struct Mol Biol. 2022;29: 1277–1290.
Naik S, Thomas NS, Davies JH, Lever M, Raponi M, Baralle D, et al. Novel Tandem Duplication in Exon 1 of the SNURF/SNRPN Gene in a Child with Transient Excessive Eating Behaviour and Weight Gain. Mol Syndromol. 2012;2: 76–80.
Keywords: translation, bicistronic