Klf6/copeb is required for hepatic outgrowth in zebrafish and for hepatocyte specification in mouse ES cells

Krüppel-like factor 6 (Klf6; copeb in zebrafish) is a zinc-finger transcription factor and tumor suppressor gene. Klf6(-/-) mice have defects in hematopoiesis and angiogenesis and do not form a liver. However, the vascular abnormalities in Klf6(-/-) mice obfuscate its role in liver development since these two processes are linked in mammals. We utilized zebrafish and mouse ES cells to investigate the role of copeb in endoderm specification and hepatogenesis separate from its function in angiogenesis. During zebrafish development, copeb expression is enriched in digestive organs. Morpholino knockdown of copeb blocks expansion of the liver, pancreas and intestine, but does not affect their specification, differentiation or the vascularization of the liver. Decreased hepatocyte proliferation in copeb morphants is accompanied by upregulation of the cell cycle inhibitor, cdkn1a, a Copeb transcriptional target. A cell autonomous role for Klf6 in endoderm and hepatic development was investigated by manipulating Klf6 expression in mouse ES cells driven to differentiate along the hepatic lineage. Expression of the endoderm markers Hnf3beta, Gata4, Sox17, and CxCr4 is not induced in Klf6(-/-) cells but is upregulated in ES cells over-expressing Klf6. Collectively, these findings indicate that copeb/Klf6 is essential for the development of endoderm-derived organs.