Cis-acting noncoding RNAs: friends and foes

In recent years, the number and types of known functional noncoding RNAs have increased considerably. A subset of both short- and long-sized species are known to be involved in the cis regulation of target genes located at or near the same genomic locus. Their expression is often coordinated with that of neighboring protein-coding genes, and in many cases, related transcripts can influence each other at one step or another during their biogenesis. Here, we review the current literature, summarizing the existing knowledge about mammalian cis-acting RNAs and their impact on physiological and disease states.