Processing of snoRNAs as a new source of regulatory non-coding RNAs: SnoRNA fragments form a new class of functional RNAs

Recent experimental evidence suggests that most of the genome is transcribed into non-coding RNAs. The initial transcripts undergo further processing generating shorter, metabolically stable RNAs with diverse functions. Small nucleolar RNAs (snoRNAs) are non-coding RNAs that modify rRNAs, tRNAs, and snRNAs that were considered stable. We review evidence that snoRNAs undergo further processing. High-throughput sequencing and RNase protection experiments showed widespread expression of snoRNA fragments, known as snoRNA-derived RNAs (sdRNAs). Some sdRNAs resemble miRNAs, these can associate with argonaute proteins and influence translation. Other sdRNAs are longer, form complexes with hnRNPs and influence gene expression. C/D box snoRNA fragmentation patterns are conserved across multiple cell types, suggesting a processing event, rather than degradation. The loss of expression from genetic loci that generate canonical snoRNAs and processed snoRNAs results in diseases, such as Prader-Willi Syndrome, indicating possible physiological roles for processed snoRNAs. We propose that processed snoRNAs acquire new roles in gene expression and represent a new class of regulatory RNAs distinct from canonical snoRNAs. Also watch the Video Abstract the same we have already done in issue 10/12 http://onlinelibrary.wiley.com/doi/10.1002/bies.201200049/abstract) Small nuclear RNAs (snoRNAs) can be further processed into shorter metabolically stable RNAs that can be subdivided into miRNAs and processed snoRNAs, collectively referred to as sdRNAs for snoRNA derived RNAs. sdRNAs form different RNA protein complexes than canonical snoRNAs and function in translational control, gene expression, and alternative splicing.