[Adult stem cells and possible mechanisms of its differentiation--editorial]

Adult stem cells are the multi-potential cells, which exist in fetal and adult tissues. It can reproduce itself (undergo self-renewal) or give rise to more specialized (differentiated) cells. Under certain inducing conditions, adult stem cells can acquire the ability to differentiate into different tissue cells. Multipotent adult progenitor cells (MAPC), an alternative name of adult stem cell given by Catherine Verfaillie, existing in bone marrow, can differentiate into cells with characteristics of mesodermal, neuroectodermal, and endodermal lineages in vitro at the single-cell level. MAPC can also contribute to most cell types when injected into the blastocyst. Adult stem cell differentiation implies that different cell lineages are derived from a single initial cell; all differentiated cell types are functional in vitro and in vivo; and engraftment is robust and persistent in the physiological and pathological situations. The possible mechanisms may underlie the differentiation: various tissue-specific stem cells are present in different organs; adult stem cells would be reprogrammed when removed from their usual microenvironment and introduced into a different niche that imparts signals to activate a novel genetic program needed for the new cell fate. And true multi-potential stem cells persist in postnatal life. In the future, multi-potent adult stem cells might then be used for therapies of degenerative or genetic disorders of multiple different organs.