Circ-ZNF609 Is a Circular RNA that Can Be Translated and Functions in Myogenesis

TLDR

Circular RNAs are covalently closed transcripts with unique structures, whose biogenesis is understood but whose physiological functions remain largely unknown. The authors profiled circRNA expression during in vitro differentiation of murine and human myoblasts, identified conserved myogenesis‑regulated species altered in Duchenne muscular dystrophy, and used a high‑content functional genomic screen to assess their roles in muscle differentiation. Circ‑ZNF609 was found to specifically regulate myoblast proliferation, contains an ORF translated into protein in a splicing‑dependent, cap‑independent manner, exemplifying a protein‑coding circRNA in eukaryotes.

Abstract

Circular RNAs (circRNAs) constitute a family of transcripts with unique structures and still largely unknown functions. Their biogenesis, which proceeds via a back-splicing reaction, is fairly well characterized, whereas their role in the modulation of physiologically relevant processes is still unclear. Here we performed expression profiling of circRNAs during in vitro differentiation of murine and human myoblasts, and we identified conserved species regulated in myogenesis and altered in Duchenne muscular dystrophy. A high-content functional genomic screen allowed the study of their functional role in muscle differentiation. One of them, circ-ZNF609, resulted in specifically controlling myoblast proliferation. Circ-ZNF609 contains an open reading frame spanning from the start codon, in common with the linear transcript, and terminating at an in-frame STOP codon, created upon circularization. Circ-ZNF609 is associated with heavy polysomes, and it is translated into a protein in a splicing-dependent and cap-independent manner, providing an example of a protein-coding circRNA in eukaryotes.