Deeply dissecting stemness: making sense to non-coding RNAs in stem cells.

Adult stem cells are an important source for the regeneration of damaged body parts. Unlike fish and amphibians, the regeneration capacity of human tissues is rather limited. Therefore, one might ask for reasons that led to the loss of regenerative capacity during evolution. Although intensive efforts have been made, we still cannot answer this question definitively. Recent advances in so-called "-omics" (e.g. transcriptomics, proteomics) technologies allowed researchers to obtain detailed views of both mRNA and protein expression levels at different time points during regeneration and tissue repair. It is now possible to make a series of snap shots to characterize stem cell activities at various stages. Recent findings have revealed an enormous plasticity of different cell types reaffirming the landscape model of cell differentiation. Apparently, differentiation of stem cells into a certain lineage is not a fixed process but rather a delicate balance, in which different signaling pathways are involved. To understand this balance, it is utmost importance to profile and catalog changes that occur during the differentiation process of stem cells both at mRNA and protein levels. In this review, we survey the impact of expression profiling on stem cell research with a particular emphasis on non-coding RNAs.