When mRNA is produced, it copies the whole gene that is being expressed. But many genes contain non-coding sequences, called introns. Post-transcriptional modifications of mRNA remove these introns - in a process called splicing - fusing the remaining exons together. These modifications also add a poly-adenine tail and a 5' cap, both of which protect the mRNA molecule from degradation.
They also found that circRNA are highly produced in brain cells. In many cases, they also stem from genes that have very important functions. The authors suggest that circRNA may be crucial to brain function, and play a key role in brain disease. The gene that had the most circRNA associated with it is called muscleblind, expressed in the brain of fruit flies. In the heads of fruit flies, muscleblind circRNA are more abundant than normal mRNA, and the authors showed that this gene can enhance and regulate the formation of its subset of circRNA molecules.
Interestingly, muscleblind is also involved in normal brain function, since defects in the sequence have been shown to cause a severe degenerative disease known as myotonic dystrophy. This disease is characterized by progressive muscle wasting and weakness, and is the most common form of adult-onset muscular dystrophy. The connection between muscleblind and circRNA suggests that these small RNA molecules may be involved in the development of myotonic dystrophy.
This study is really interesting because it not only deepens our understanding of molecular biology and the complexity of gene expression, but it also provides new avenues for studying and treating degenerative diseases of the brain and muscles. Additionally, another study reported altered levels of CDR1as/ciRS-7 in patients with Alzheimer's disease, further supporting the idea that circRNA play a role in degenerative disease. I'm looking forward to seeing more exciting results linking the two in the future!