Biology subjects

Guo, J. U.

Publications and source records attributed to Guo, J. U..

6 recordsLinked to original sources

bioRxiv2024

Alternative translation initiation produces synaptic organizer proteoforms with distinct localization and functions

While previous studies suggest that many mRNAs contain more than one translation initiation site (TIS), the biological significance of most alternative TISs and their corresponding protein isoforms (proteoforms) remains undetermined. Here we show that alternative translation initiation at a CUG and an AUG TIS in neuronal pentraxin receptor (NPR) mRNA produces two proteoforms, and their relative abundance is regulated by both neuronal activity as well as an adjacent RNA secondary structure. Downstream AUG initiation transforms the N-terminal transmembrane domain into a signal peptide, thereby converting NPR to a secreted factor sufficient to promote synaptic clustering of AMPA-type glutamate receptors. Changing the relative proteoform ratio, but not the overall NPR abundance reduces AMPA receptor in parvalbumin (PV)-positive interneurons and induces changes in learning behaviors in mice. In addition to NPR, N-terminal extensions of C1q-like synaptic organizers, mediated by upstream AUU start codons, anchor these otherwise secreted factors to the membrane. Thus, our results uncovered the plasticity of N-terminal signal sequences regulated by alternative TIS usage as a widespread mechanism to diversify protein localization and functions.

molecular biology↗

bioRxiv2023

Aberrant splicing exonizes C9ORF72 repeat expansion in ALS/FTD

A nucleotide repeat expansion (NRE) in the first annotated intron of the C9ORF72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). While C9 NRE-containing RNAs can be translated into several toxic dipeptide repeat proteins, how an intronic NRE can assess the translation machinery in the cytoplasm remains unclear. By capturing and sequencing NRE-containing RNAs from patient-derived cells, we found that C9 NRE was exonized by the usage of downstream 5' splice sites and exported from the nucleus in a variety of spliced mRNA isoforms. C9ORF72 aberrant splicing was substantially elevated in both C9 NRE+ motor neurons and human brain tissues. Furthermore, NREs above the pathological threshold were sufficient to activate cryptic splice sites in reporter mRNAs. In summary, our results revealed a crucial and potentially widespread role of repeat-induced aberrant splicing in the biogenesis, localization, and translation of NRE-containing RNAs.

neuroscience↗

bioRxiv2023

Genome-wide CRISPR screens identify noncanonical translation factor eIF2A as an enhancer of SARS-CoV-2 programmed -1 ribosomal frameshifting

Many positive-strand RNA viruses, including all known coronaviruses, employ programmed -1 ribosomal frameshifting (-1 PRF) to regulate the translation of polycistronic viral RNAs. However, only a few host factors have been shown to regulate -1 PRF. Through a reporter-based genome-wide CRISPR/Cas9 knockout screen, we identified several host factors that either suppressed or enhanced -1 PRF of SARS-CoV-2. One of these factors is eukaryotic translation initiation factor 2A (eIF2A), which specifically and directly enhanced -1 PRF in vitro and in cells. Consistent with the crucial role of efficient -1 PRF in transcriptase/replicase expression, loss of eIF2A reduced SARS-CoV-2 replication in cells. Transcriptome-wide analysis of eIF2A-interacting RNAs showed that eIF2A primarily interacted with 18S ribosomal RNA near the contacts between the SARS-CoV-2 frameshift-stimulatory element (FSE) and the ribosome. Thus, our results revealed an unexpected role for eIF2A in modulating the translation of specific RNAs independent of its previously described role during initiation.

molecular biology↗

bioRxiv2022

Systematic generation and imaging of tandem repeats reveal multivalent base-pairing as a major determinant of RNA aggregation

Expansion of short tandem repeats (STRs) in the human genome underlies over fifty genetic disorders. A common pathological feature of repeat RNAs is their propensity to aggregate in cells. While these RNA aggregates have been shown to cause toxicity by sequestering RNA-binding proteins, the molecular mechanism of repeat RNA aggregation remains unclear. Here we devised a generalizable method to efficiently generate long tandem repeat DNAs de novo and applied it to systematically determine the sequence features underlying RNA aggregation. Live-cell imaging of repeat RNAs indicated that aggregation was mainly driven by multivalent RNA-RNA interactions via either canonical or noncanonical base pairs. While multiple short runs of two consecutive base pairs were sufficient, longer runs of consecutive base pairs such as those formed by a neurodegeneration-associated hexanucleotide repeat further enhanced aggregation. In summary, our study provides a unifying model for the molecular basis of repeat RNA aggregation and a generalizable approach for identifying the sequence and structural determinants of repeat RNA properties.

molecular biology↗

bioRxiv2020

Restriction of SARS-CoV-2 Replication by Targeting Programmed -1 Ribosomal Frameshifting In Vitro

Translation of open reading frame 1b (ORF1b) in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) requires programmed -1 ribosomal frameshifting (-1 PRF) promoted by an RNA pseudoknot. The extent to which SARS-CoV-2 replication may be sensitive to changes in -1 PRF efficiency is currently unknown. Through an unbiased, reporter-based high-throughput compound screen, we identified merafloxacin, a fluoroquinolone antibacterial, as a -1 PRF inhibitor of SARS-CoV-2. Frameshift inhibition by merafloxacin is robust to mutations within the pseudoknot region and is similarly effective on -1 PRF of other beta coronaviruses. Importantly, frameshift inhibition by merafloxacin substantially impedes SARS-CoV-2 replication in Vero E6 cells, thereby providing the proof of principle of targeting -1 PRF as an effective antiviral strategy for SARS-CoV-2.

molecular biology↗

bioRxiv2019

C9orf72 dipeptide repeats inhibit UPF1-mediated RNA decay independent of stress granule formation

Expansion of an intronic (GGGGCC)n repeat region within the C9orf72 gene is a major cause of familial amyotrophic lateral sclerosis and frontotemporal dementia (c9ALS/FTD). A pathological hallmark in c9ALS/FTD is the accumulation of misprocessed RNAs, which are often targets of RNA surveillance pathways in normal cells. Here we show that nonsense-mediated decay (NMD) and other RNA decay mechanisms involving upstream frameshift 1 (UPF1), collectively referred to as UPF1-mediated RNA decay (UMD), are broadly inhibited in c9ALS/FTD brains. These effects are recapitulated in cultured cells by the ectopic expression of arginine-rich dipeptide repeats (DPRs), poly(GR) and poly(PR). Despite these two DPRs causing the recruitment of UPF1 to stress granules, stress granule formation is neither sufficient nor necessary for UMD inhibition. Our results suggest that UMD inhibition may accelerate the accumulation of deleterious RNAs and polypeptides in c9ALS/FTD.

molecular biology↗