[MicroRNA and central nervous system]

MicroRNAs (miRNAs) are 21-24 nucleotide (nt) duplex RNAs that participate in the translational regulation of messenger RNAs (mRNA). These miRNAs are created from precursor transcripts by subsequent processing steps that are mediated by Drosha and Dicer-members of the RNAseIII family. One of the two strands is incorporated into the active sites of a protein that belongs to the argonaute family of proteins, where it serves as a guide for complementary sequences in the 3'-UTR site of the target mRNAs. miRNAs are expressed at high levels within the as well as mature developing brain. These miRNAs orchestrate the maintenance of adult neural cell traits, promote cellular homeostasis and dampen endogenous and exogenous stress responses, and modulate multiple parameters that are associated with synaptic plasticity. In this regard, the expression of a brain-specific miRNA (miR-124a) in nonneuronal cells enables the conversion of the overall gene-expression pattern to a neuronal one. Another brain-specific miRNA, namely, miR-134, modulates the development of dendritic spines-neuronal protrusions that connect with other neurons-and therefore probably controls neuronal transmission and plasticity. Recent evidence suggests that miRNAs may be a contributing factor cases of neurodegeneration, such as those in Alzheimer diseases and polyglutamine diseases. Research on miRNAs in the context of neurodegeneration has been rapidly advancing, and the goal of this review is to provide perspective for new data that may aid specialists in this field.