Roles of small regulatory RNAs in determining neuronal identity

The small regulatory RNAs identified so far include microRNAs (miRNAs), endogenous small interfering RNAs (esiRNAs), Piwi-interacting RNAs (piRNAs) and promoter-associated short RNAs (PASRs; also known as transcription start site RNAs (TSS RNAs) and transcription initiation RNAs (tiRNAs)). These small RNAs range from 18–30 nucleotides in length and can modulate diverse cellular pathways.The specific expression of miRNA in the nervous system suggests that miRNAs could play key parts in brain development and neuronal fate specification.It has been shown that transcription factors can directly regulate the expression of specific miRNAs and that specific miRNAs can then target other transcription factors and regulate their expression post-transcriptionally. The result is a transcription factor to miRNA to another transcription factor (sometimes even of the miRNA itself) paradigm for regulating neurogenesis.During neurogenesis, miRNAs may act through feedback loops to reinforce and stabilize changes in gene expression in response to signalling input.Recent evidence suggests that an epigenetic circuitory with a feedback regulatory mechanism mediated by miRNAs is involved in the regulation of neurogenesis.miRNAs that determine the lineage specificity of both astrocytes and oligodendrocytes have been identified.Other types of small regulatory RNAs could also be involved in regulating neurogenesis. Powerful deep-sequencing technologies should enable the identification of many more small regulatory RNAs that are involved in regulating neurogenesis.