Circular RNAs expression and function in myogenesis

Skeletal myogenesis is a well-characterized biological process driving the formation of the adult muscle tissue from mesodermal progenitors. The key molecular and cellular steps of such process can be replicated in vitro, by culturing muscle precursor cells called myoblasts, which can be induced to differentiate into mature myotubes. We characterized the role of a long non-coding RNA, linc-MD1, in regulating in vitro differentiation of murine myoblasts by acting as a molecular decoy for two microRNAs, miR-133 and miR-135, and we further dissected the regulation of linc-MD1 biosynthesis by the RNA binding protein HuR. Searching for new non-canonical RNA species involved in myogenesis, we directed our attention to circular RNAs (circRNAs). Circular RNAs are produced by the spliceosome via a particular reaction called back-splicing, which links a donor splice site to an upstream acceptor site, thereby generating a covalently closed RNA molecule. We performed high-throughput expression profiling of circRNAs in murine and human cells and studied the principles of their regulation during myogenesis. We then applied a high-content functional genomic screen of conserved circRNAs and found that these molecules are actively involved in the control of myoblasts differentiation. Among them, we further characterized circ-ZNF609 and found that it is able to control myoblast proliferation, providing the first example of a circular RNA involved in a relevant biological process. Moreover, sequence and biochemical analyses suggested that circ-ZNF609 might be translated in a functional protein, representing a possible molecular mechanism for circRNA function.