Modeling Vertebrate Adult Stem Cells and Their Progeny

Abstract

Classical studies on hematopoiesis indicate that blood cell numbers are maintained by a rare, hard-wired, transplantable stem cell (SC). Subsequent studies in other organs have implicitly assumed that all SC hierarchies follow the design of the hematopoietic system. Lineage tracing techniques have revolutionized the study of solid tissue SCs. It thus appears that key characteristics of the hematopoietic SC hierarchy (rarity of the SC, expression of specific markers, quiescence, asymmetric division, unidirectional differentiation) are not generalizable to other tissues. It is concluded that the only generalizable definition of SC function is the ability to replace lost tissue through cell division.