Information Processing Biology Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa 904-0495, Japan.
Genetics. 2021 Nov 5;219(3). doi: 10.1093/genetics/iyab145.
Many circular RNAs (circRNAs) are differentially expressed in different tissues or cell types, suggestive of specific factors that regulate their biogenesis. Here, taking advantage of available mutation strains of RNA-binding proteins (RBPs) in Caenorhabditis elegans, I performed a screening of circRNA regulation in 13 conserved RBPs. Among them, loss of FUST-1, the homolog of Fused in Sarcoma (FUS), caused downregulation of multiple circRNAs. By rescue experiments, I confirmed FUST-1 as a circRNA regulator. Through RNA sequencing using circRNA-enriched samples, circRNAs targets regulated by FUST-1 were identified globally, with hundreds of them significantly altered. Furthermore, I showed that FUST-1 regulates circRNA formation with only small to little effect on the cognate linear mRNAs. When recognizing circRNA pre-mRNAs, FUST-1 can affect both exon-skipping and circRNA in the same genes. Moreover, I identified an autoregulation loop in fust-1, where FUST-1, isoform a (FUST-1A) promotes the skipping of exon 5 of its own pre-mRNA, which produces FUST-1, isoform b (FUST-1B) with different N-terminal sequences. FUST-1A is the functional isoform in circRNA regulation. Although FUST-1B has the same functional domains as FUST-1A, it cannot regulate either exon-skipping or circRNA formation. This study provided an in vivo investigation of circRNA regulation, which will be helpful to understand the mechanisms that govern circRNA formation.
许多环状 RNA（circRNA）在不同组织或细胞类型中表达差异，提示存在特定的因素调节其生物发生。在这里，我利用线虫中可用的 RNA 结合蛋白（RBP）突变株，对 13 个保守 RBP 的 circRNA 调控进行了筛选。其中，FUS 同源物 FUST-1 的缺失导致多种 circRNA 的下调。通过 rescue 实验，我证实了 FUST-1 是 circRNA 的调节因子。通过使用 circRNA 富集样本进行 RNA 测序，鉴定了 FUST-1 调控的 circRNA 靶点，其中数百个靶标circRNA 显著改变。此外，我表明 FUST-1 通过 circRNA 前体 RNA 调节 circRNA 的形成，对同源线性 mRNA 的影响较小。当识别 circRNA 前体 RNA 时，FUST-1 可以在同一基因中同时影响外显子跳跃和 circRNA。此外，我在 fust-1 中鉴定出一个自调控环，其中 FUST-1，异构体 a（FUST-1A）促进其自身前体 RNA 外显子 5 的跳跃，产生具有不同 N 端序列的 FUST-1，异构体 b（FUST-1B）。FUST-1A 是 circRNA 调节中的功能性异构体。尽管 FUST-1B 与 FUST-1A 具有相同的功能结构域，但它不能调节外显子跳跃或 circRNA 的形成。这项研究提供了 circRNA 调控的体内研究，有助于理解控制 circRNA 形成的机制。
