ABSTRACT
This chapter focuses on microRNAs (miRNAs), which are the smallest member among all known non-coding RNAs (ncRNAs). MiRNA coding genes are located either within the introns or exons of protein-coding genes or in intergenic areas, and mostly found to be evolutionarily conserved. Biogenesis of miRNAs involves multistep processes that can be divided into transcription, nuclear cropping, export to the cytoplasm, and cytoplasmic dicing. Like a protein-coding gene, a miRNA can act as a tumor suppressor when its loss of function is related to malignant transformation of a normal cell. The loss of function of a miRNA can be a result of genomic deletion, mutation, epigenetic silencing, and/or miRNA processing alterations. Overall frequency of Single Polymorphism (SNP) in miRNA-binding site or SNP in miRNA sequences was predicted to be less than 1%, due to the size of miRNA and its binding site. In 2003, stem cell-specific miRNA signature was first described in mouse embryonic stem cells.
