MicroRNAs: key regulators of stem cells

Embryonic and adult tissue stem cells are characterized by their ability to self-renew and to differentiate into daughter cells, which in adult tissue stem cells is often achieved by asymmetric divisions.MicroRNAs (miRNAs) are 20–25-nucleotide (nt)-long non-coding RNAs that bind to the 3′ untranslated region of target mRNAs via imperfect match to repress their translation and stability.miRNAs fine-tune self-renewal and differentiation pathways of stem cells by regulating the intracellular levels of the key protein factors that are involved in these processes. It is now clear that a number of miRNAs that are involved in stem cell processes are co-expressed as clusters and can function as 'master regulators' of stem cell processes.miRNAs and the transcriptional machinery form an integral network that regulates stem cell processes.In addition to miRNA, there are two other types of small RNAs: endogenous small interfering RNAs (endo-siRNAs) and Piwi-interacting RNAs (piRNAs). Their presence and function in stem cells is not known.The recent advent of next generation sequencing technologies has increased our ability to identify new miRNAs and other small RNAs in various tissues.