FUS affects circular RNA expression in murine embryonic stem cell-derived motor neurons

Abstract

The RNA-binding protein FUS participates in several RNA biosynthetic processes and has been linked to the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. Here we report that FUS controls back-splicing reactions leading to circular RNA (circRNA) production. We identified circRNAs expressed in in vitro-derived mouse motor neurons (MNs) and determined that the production of a considerable number of these circRNAs is regulated by FUS. Using RNAi and overexpression of wild-type and ALS-associated FUS mutants, we directly correlate the modulation of circRNA biogenesis with alteration of FUS nuclear levels and with putative toxic gain of function activities. We also demonstrate that FUS regulates circRNA biogenesis by binding the introns flanking the back-splicing junctions and that this control can be reproduced with artificial constructs. Most circRNAs are conserved in humans and specific ones are deregulated in human-induced pluripotent stem cell-derived MNs carrying the FUSP525L mutation associated with ALS.

Past, present, and future of circ RNA s

“…QKI promotes global circRNA production during the epithelial-to-mesenchymal transformation in human cell culture by binding to intronic sequences surrounding the circularized exons (Conn et al, 2015). FUS regulates circRNA formation in murine embryonic stem cell-derived motor neurons by binding to specific exon-intron junctions (Errichelli et al, 2017). FUS regulates circRNA formation in murine embryonic stem cell-derived motor neurons by binding to specific exon-intron junctions (Errichelli et al, 2017).…”

“…Interestingly, like MBL, QKI might dimerize to facilitate circularization (Teplova et al, 2013). FUS regulates circRNA formation in murine embryonic stem cell-derived motor neurons by binding to specific exon-intron junctions (Errichelli et al, 2017). In addition, the splicing factor ESRP1 mediates circularization of circBIRC6 (derived from the baculoviral IAP repeatcontaining 6 gene) by binding to specific sites that are present in the introns flanking the circularizable exon (Yu et al, 2017).…”

“…Hence, biogenesis of circRNA results in reduced synthesis of mRNAs from the same locus. Later works identified other RNA-binding proteins (RBPs) that regulate exon circularization in different systems and organisms; these include adenosine deaminases acting on RNA (ADAR), quaking (QKI), FUS, nuclear factors NF90/NF110, DExH-Box helicase 9 (DHX9), epithelial splicing regulatory protein 1 (ESRP1), and serine/arginine (SR)-rich proteins (Conn et al, 2015;Ivanov et al, 2015;Kramer et al, 2015;Rybak-Wolf et al, 2015;Aktas et al, 2017;Errichelli et al, 2017;Li et al, 2017a;Yu et al, 2017). Several groups identified requirements for splicing and circularization of exons and demonstrated that circularization signals are located within the introns flanking the circularizable exons (Jeck et al, 2013;Ashwal-Fluss et al, 2014;Liang & Wilusz, 2014;Wang et al, 2014;Zhang et al, 2014;Ivanov et al, 2015;Rybak-Wolf et al, 2015;Starke et al, 2015;Veno et al, 2015;Sun et al, 2016;Zhang et al, 2016b).…”

“…Ashwal-Fluss et al (2014) also suggested the existence of a negative-feedback loop for the regulation of circMbl production in flies and identified the first protein involved in exon circularization [the splicing factor muscleblind (MBL) in Drosophila and the vertebrate homolog muscleblind-like protein 1 (MBNL1)]. Later works identified other RNA-binding proteins (RBPs) that regulate exon circularization in different systems and organisms; these include adenosine deaminases acting on RNA (ADAR), quaking (QKI), FUS, nuclear factors NF90/NF110, DExH-Box helicase 9 (DHX9), epithelial splicing regulatory protein 1 (ESRP1), and serine/arginine (SR)-rich proteins (Conn et al, 2015;Ivanov et al, 2015;Kramer et al, 2015;Rybak-Wolf et al, 2015;Aktas et al, 2017;Errichelli et al, 2017;Li et al, 2017a;Yu et al, 2017).…”

Transcriptome-wide profiles of circular RNA and RNA binding protein interactions reveal effects on circular RNA biogenesis and cancer pathway expression

“…Recent studies have shown that RBPs also affect all phases of the circRNA lifecycle (reviewed in (14) ). Some RBPs are involved in circRNA biogenesis as has been shown for Quaking (QKI) (15) , FUS (16) , HNRNPL (17) , RBM20 (18) , and Muscleblind (19) , which bind to specific intronic RBP motifs and promote formation of some circRNAs in certain biological settings. Besides RBP binding motifs, complementary sequences in both flanking introns, like Alu elements, facilitate circRNA production by RNA pairing (4) .…”