Molecular mechanisms of liver and bile duct development.

The liver is derived from the ventral foregut endoderm. After hepatic specification, liver progenitor cells delaminate from the endoderm and invade the septum transversum mesenchyme to form the liver bud. In addition to proliferation and expansion, liver progenitor cells differentiate into two epithelial cell types, each arranged into unique structures with distinctive function. Growth, morphogenesis, and differentiation during liver development are regulated by a variety of factors that are expressed in a spatially and temporally specific manner. A comprehensive understanding of the regulatory mechanisms underlying the liver development has influenced the diagnosis of liver diseases and further progress will be critical for future advances in therapy. This review highlights some of the best understood steps of liver development, summarizing progress in our understanding of the molecular mechanisms that underlie differentiation, morphogenesis, and functional integration of the liver.