The dynamic stem cell microenvironment is orchestrated by microvesicle-mediated transfer of genetic information

It has been commonly supposed that adult stem cells co-localize with supporting cells within specific regions or specialized microenvironment in each tissue/organ, called stem cell niche. This concept was based on the assumption that stem cells are intrinsically hierarchical in nature. However, recent data indicate that stem cells may represent a continuum with reversible alterations in phenotype taking place during the transit through cell cycle. Based on this dynamic interpretation it has been suggested that the so-called niche is represented by a single or only few cell types continually adjusting their phenotype and function to individual circumstances. A critical component in the regulation of the continuum of stem cell phenotypes is the microenvironment. In this context, microvesicles (MVs) account for the transfer of genetic information between cells. Originally considered inert cellular debris, MVs are increasingly recognized to be important mediators of cell-to-cell communication. MVs may transfer receptors, proteins, mRNA and microRNA to target cells via specific receptor-mediated interaction. In stem cell biology the exchange of genetic information may be bidirectional from stromal to stem cells. In the context of tissue injury the MV-mediated transfer of genetic information may reprogram the phenotype of stem cells to acquire features of the injured tissue cells. In addition, MVs derived from stem cells may induce de-differentiation of cells which have survived injury with a cell cycle re-entry that may allow tissue regeneration. In the present review we discuss the possibility of a continuous genetic modulation of stem cells by a MV-mediated transfer of information between cells.