The mouse Forkhead Box m1 transcription factor is essential for hepatoblast mitosis and development of intrahepatic bile ducts and vessels during liver morphogenesis

Abstract

Conditional deletion of the mouse Forkhead Box (Fox) m1b targeted allele in adult hepatocytes (Foxm1, previously called HFH-11B, Trident, Win, or MPP2) demonstrated that the Foxm1b transcription factor is essential for hepatocyte mitosis during liver regeneration. To determine the role of Foxm1b in liver development, we have generated Foxm1b -/- mice that deleted the Foxm1b exons encoding the winged helix DNA binding and transcriptional activation domains. Here, we show that all of the Foxm1b -/- embryos died in utero by 18.5 days postcoitum (dpc). Embryonic Foxm1b -/- livers displayed a 75% reduction in the number of hepatoblasts, resulting from diminished DNA replication and a failure to enter mitosis causing a polyploid phenotype. Reduced hepatoblast mitosis was associated with decreased protein levels of the Polo-like kinase 1 and Aurora B kinase, which phosphorylate regulatory proteins essential for orchestrating mitosis and cytokinesis. Diminished proliferation of Foxm1b -/- hepatoblasts contributed to abnormal liver development with significant reduction in the number of large hepatic veins compared to embryonic wild-type (WT) liver. Furthermore, embryonic Foxm1b -/- livers did not develop intrahepatic bile ducts, and these presumptive biliary hepatoblasts failed to express either biliary cytokeratins or nuclear levels of hepatocyte nuclear factor 1beta. These results suggest that Foxm1b is critical for hepatoblast precursor cells to differentiate toward biliary epithelial cell lineage. Finally, we used a hepatoblast-specific Cre recombinase transgene to mediate deletion of the Foxm1b fl/fl allele in the developing liver, and these embryos died in utero and exhibited diminished hepatoblast proliferation with similar abnormalities in liver morphogenesis, suggesting that the defect in liver development contributed to embryonic lethality.

Transgenic expression of the forkhead box M1 transcription factor induces formation of lung tumors

“…Foxm1 transcription factor regulates expression of genes essential for DNA replication and mitosis during a variety of biological processes including embryonic development, organ injury and cancer formation (Kalinichenko et al, 2003;Krupczak-Hollis et al, 2004;Kim et al, 2005a). Consistent with the important role of Foxm1 in cell cycle progression, elevated Foxm1 levels have been found in a variety of tumor cell lines (Korver et al, 1997;Ye et al, 1997) as well as numerous types of human tumors (Teh et al, 2002;van den Boom et al, 2003;Lee et al, 2004;Obama et al, 2005;Wonsey and Follettie, 2005;Kalin et al, 2006).…”

“…The Foxm1 protein also stimulates transcription of Skp2 and Cks1 genes, which are specificity subunits of the Skp1-Cullin-F-Box ubiquitin ligase complex that targets the Cdk inhibitors p27 kip1 and p21 cip1 for degradation during the G 1 /S transition (Wang et al, 2005). We previously demonstrated that Foxm1 À/À mice exhibit embryonic lethality due to severe abnormalities in development of the heart, liver and lung (Krupczak-Hollis et al, 2004;Kim et al, 2005a). This is caused by a failure to complete mitosis, causing a significant reduction in the number of cells in these developing mouse organs (Krupczak-Hollis et al, 2004;Kim et al, 2005a).…”

“…We previously demonstrated that Foxm1 À/À mice exhibit embryonic lethality due to severe abnormalities in development of the heart, liver and lung (Krupczak-Hollis et al, 2004;Kim et al, 2005a). This is caused by a failure to complete mitosis, causing a significant reduction in the number of cells in these developing mouse organs (Krupczak-Hollis et al, 2004;Kim et al, 2005a).…”

Myocardium defects and ventricular hypoplasia in mice homozygous null for the Forkhead Box m1 transcription factor

“…Although the Foxm1 Ϫ/Ϫneo mice died postnatally, displaying accumulation of polyploid cardiomyocytes and hepatoblasts (Korver et al, 1998), the authors did not provide any molecular mechanisms of this cardiovascular phenotype and, therefore, the precise role of Foxm1 during heart development remains uncharacterized. We generated a distinct Foxm1 Ϫ/Ϫ mouse line, which contains a targeted deletion of exons 4 to 7 encoding the Foxm1 winged helix DNA binding and the C-terminal transcriptional activation domains (Krupczak-Hollis et al, 2004). Most of the Foxm1 Ϫ/Ϫ embryos died in utero between 13.5 and 16.5 dpc due to severe defects in development of the embryonic liver, lung, and heart (Krupczak-Hollis et al, 2004;Kim et al, 2005a).…”

“…We generated a distinct Foxm1 Ϫ/Ϫ mouse line, which contains a targeted deletion of exons 4 to 7 encoding the Foxm1 winged helix DNA binding and the C-terminal transcriptional activation domains (Krupczak-Hollis et al, 2004). Most of the Foxm1 Ϫ/Ϫ embryos died in utero between 13.5 and 16.5 dpc due to severe defects in development of the embryonic liver, lung, and heart (Krupczak-Hollis et al, 2004;Kim et al, 2005a). Foxm1 Ϫ/Ϫ livers displayed abnormal accumulation of polyploid hepatoblasts resulting from diminished DNA replication and a failure to enter mitosis (Krupczak-Hollis et al, 2004).…”