Stable Intronic Sequence RNAs (sisRNAs): An Expanding Universe.

Intronic sequences are often regarded as 'nonsense' transcripts that are rapidly degraded. We highlight here recent studies on intronic sequences that play regulatory roles as long noncoding RNAs (lncRNAs) which are classified as sisRNAs. Interestingly, sisRNAs come in different forms and are produced via a variety of ways. They regulate genes at the DNA, RNA, and protein levels, and frequently engage in autoregulatory feedback loops to ensure cellular homeostasis under normal and stress conditions. Future directions, evolutionary insights, and potential implications of dysregulated sisRNAs are also discussed, especially in relation to human pathogenesis.