MicroRNAs in learning, memory, and neurological diseases.

MicroRNAs (miRNAs) represent a class of small regulatory noncoding RNAs ∼22 bp in length that mediate post-transcriptional silencing of gene expression via the recognition of specific sequences in target messenger (m)RNAs. The current body of literature suggests that miRNAs are fine-tuning regulators of gene expression profiles in a wide range of biological processes, from development to cancer. Many miRNAs are highly expressed in the adult nervous system in a spatially and temporally controlled manner in normal physiology, as well as in certain pathological conditions. These findings emphasize that gene regulation networks based on miRNA activities may be particularly important to brain function, and that perturbation of these networks may result in abnormal brain function. Indeed, miRNAs have been implicated in various aspects of dendrite remodeling and synaptic plasticity, as well as in experience-dependent adaptive changes of neural circuits in the postnatal developmental and adult brain. Recent advances in methods of next-generation sequencing, such as RNA-seq, offer the means to quantitatively evaluate the functions of miRNAs in a genome-wide manner in large cohorts of samples. These new technologies have already yielded valuable information and are expanding our understanding of miRNA-based mechanisms in higher-order brain processing, including learning and memory and cognition, as well as in neuropsychiatric disorders.