Differentiation of the mouse hepatic primordium cultured in vitro.

The differentiation of hepatic endodermal cells is affected by endodermal-mesodermal interactions. To examine the control mechanisms of this differentiation, we cultured mouse liver primordium and tissue recombinants of the hepatic endoderm with homo- or heterologous mesenchyme in vitro. When the hepatic primordia at somite stages 15-23 were cultured in vitro for 5-10 days, the endodermal cells differentiated into large hepatocytes expressing alpha-fetoprotein (AFP), albumin and carbamoylphosphate synthetase I (CPSI) and storing glycogen. AFP continued to be expressed in hepatocytes through culture for 10 days. Albumin and CPSI expression started in hepatocytes at 1 and 2 days after culture, respectively. Dexamethasone stimulated hepatocyte differentiation (expression of CPSI and glycogen accumulation) and large lumen formation of hepatocytes, but it did not change the commencement of differentiation. When the hepatic endoderm was recombined with hepatic mesenchyme or 4-day embryonic chick lung mesenchyme, clotted in Matrigel, which is a basement-membrane-like substratum, and cultured for 5 days in vitro, it differentiated into large hepatocytes expressing albumin and CPSI and accumulating glycogen. Lung mesenchyme promoted duct formation more efficiently than the hepatic mesenchyme did. However, the hepatic endodermal cells failed to differentiate into large hepatocytes when cultured with 6-day embryonic chick metanephric mesenchyme or with 2.5-day chick somitic mesenchyme, or cultured alone in Matrigel, suggesting that the endodermal cells require the presence of splanchnic mesoderm for their differentiation in vitro. Addition of HGF (hepatocyte growth factor), aFGF (acidic fibroblast growth factor), or bFGF (basic fibroblast growth factor) also did not support the survival of hepatic endodermal cells or hepatocyte differentiation in culture without mesenchyme. Matrigel and those growth factors might not be a suitable substitute for the mesenchyme.