Gastrointestinal stem cells. III. Emergent themes of liver stem cell biology: niche, quiescence, self-renewal, and plasticity.

This essay will address areas of liver stem/progenitor cell studies in which consensus has emerged and in which controversy still prevails over consensus, but it will also highlight important themes that inevitably should be a focus of liver stem/progenitor cell investigations in coming years. Thus concepts regarding cell plasticity, the existence of a physiological/anatomic stem cell niche, and whether intrahepatic liver stem/progenitor cells comprise true stem cells or progenitor cells (or both) will be approached in some detail.