Differentiation of the mouse hepatic primordium. II. Extrinsic origin of the haemopoietic cell line.

The whole hepatic primordium (endoderm + mesenchyme of the septum transversum) was isolated from mouse embryos at various developmental stages, from 8 to 10 days of gestation, and was either grafted into chick or quail embryo or cultivated in vitro. Haemopoiesis developed only if the liver rudiment had been explanted after the 28- to 30-somite stage, but not if explanted prior to this stage, despite normal differentiation of the hepatocytes. However, when the liver rudiment, isolated before the 28-somite stage in in vitro culture, was supplied with exogenous haemopoietic stem cells, haemopoiesis developed in the hepatic tissue. These data show that foetal hepatic haemopoiesis depends on migration of haemopoietic cells which home the liver rudiment at the 28- to 30-somite stage.