Hepatocyte differentiation: from the endoderm and beyond

Hepatocytes differentiate from the endoderm during embryonic development. R ecent studies show, however, that hepatocytes can also be derived from rare cells that reside in the pancreas, bone marrow, and brain. Indeed, the lat est discoveries indicate that embryonic hepatocytes normally arise by diver sion of an endodermal cell population that would otherwise default to a pan creatic fate. Convergent FGF and BMP signals from distinct mesodermal cell types control this transition. Molecular signals that govern the differenti ation of hepatocytes from non-endodermal cells and the role of such cells i n normal liver physiology remain to be discovered.