Induction of hepatic differentiation in embryonic stem cells by co-culture with embryonic cardiac mesoderm

Background. Modifications in vitro have been used to direct embryonic stem (ES) cells toward endodermal phenotypes including hepatocytes; however, developmental correlates and evidence of biologic activity is lacking, and critical cell-cell interactions have not been investigated. In this study, we hypothesized that cardiac mesoderm (CM) signals ES cells in co-culture to undergo differentiation toward early hepatocyte lineage as determined by morphology and induction of genes essential for endodermal competence and hepatocyte development. Methods. Green fluorescent protein ES derived from A 129 mice were cultured with or without embryonic chick cardiac mesoderm. Cultures from day 1, 2, and 4 were analyzed for colony formation and ES morphology and 106 ES-derived cells were isolated for mRNA analysis. Results. ES in co-culture with CM displayed colony formation, polymorphic appearance, and definitive interface with CM. In addition, ES + CM co-culture activated crucial transcription factors (sox 17alpha, HNF3beta, and GATA 4) required for hepatocyte development by day 1. mRNA for albumin and especially alpha-fetoprotein were also increased by culture days 2 and 4. Conclusions. ES cells co-cultured with CM display morphology and gene expression pattern required for hepatocyte differentiation and appear to recapitulate the molecular events of hepatogenesis.