In addition to regulating gene expression, cocaine may also influence neuroplastic responses in brain reward systems by influencing gene translation. One recently implicated mechanism of post-transcriptional gene regulation through which cocaine may act is through the miRNAs. The miRNAs are a class of small ncRNAs68-70 that regulate gene expression through direct binding to the 3' UTR of gene targets and blocking their translation into encoded protein or triggering their destabilization and degradation.71 Many hundreds of miRNA species have been identified in plants and animals.72-76 In animals, miRNAs bind to the 3'UTR of target transcripts by incomplete complementary base-pairing, particularly at a portion of the 5' end of the miRNA termed the miRNA “seed” region. This imprecise complementary base-pairing means that potentially many hundreds of mammalian gene transcripts can be regulated by a single miRNA.
