Reading the SINEs – functionality in noncoding RNA ‘cheap genes’

SINEs (Short Interspersed Nuclear Elements) are a class of retrotransposons, among the most prolific and transcriptionally active groups of repetitive elements. Rodent B1/B2-SINEs and primate Alu RNAs are upregulated in stress responses such as cellular heat shock or upon viral infection. Here we review recent findings demonstrating that SINE RNAs have also integrated as adaptive regulators of gene expression in different biological contexts, particularly in nervous system lesion, degeneration and remodelling. These integral roles in physiological processes reinforce the concept that SINEs provide 'cheap genes' for evolutionary adaptation of non-coding RNA to biological function.