Liver-enriched transcription factors and hepatocyte differentiation.

Liver-specific gene expression in adult hepatocytes relies on four families of evolutionary conserved transcription factors that are liver-enriched but not restricted to this tissue. These factors function in unique combinations, often synergistically, to stimulate cell-specific transcription. Each family is composed of several members displaying similar, if not identical, DNA recognition properties and sharing structural homology in their DNA binding domains. The homo- and heterodimerization between members of a particular transcription factor family adds an additional level of complexity in gene regulation. The consequences of inactivating different family members in the mouse by homologous recombination, together with recent studies of their regulation, suggest a model for liver differentiation involving a regulatory network rather than a completely hierarchical genetic circuitry. These studies also indicate that individual regulators appear to serve multiple developmental functions. Their possible role in the progression through different stages of hepatic cell commitment and differentiation is discussed.