Uncoupling of S phase and mitosis in cardiomyocytes and hepatocytes lacking the winged-helix transcription factor Trident

Abstract

In order to maintain a stable karyotype, the eukaryotic cell cycle is coordinated such that only one round of S phase precedes each mitosis, and mitosis is not initiated until DNA replication is completed. Several checkpoints and regulatory proteins have been defined in lower eukaryotes that govern this coordination, but little is known about the proteins that are involved in mammalian cells. Previously, we have shown that the winged-helix transcription factor Trident - also known as HFH-11, FKL16 and WIN [1] [2] [3] - is exclusively expressed in cycling cells and is phosphorylated during mitosis [1] [4]. The cellular function of Trident has yet to be described, however. Here, we have shown that disruption of the Trident gene in mice resulted in postnatal death, most probably because of circulatory failure. Histological analysis of Trident -/- embryos from embryonic day 10 (E10) onwards revealed a specific, characteristic defect in the developing myocardium. The orientation of the myocytes was highly irregular and the nuclei of these disorganized cardiomyocytes were clearly polyploid with up to a 50-fold increase in DNA content. Polyploidy was also observed in embryonic hepatocytes. Our results indicate that expression of Trident is required to prevent multiple rounds of S phase in the heart and the liver. Trident therefore appears to have a role in preventing DNA re-replication during the G2 and M phases.

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

“…Most of the Foxm1 Ϫ/Ϫ embryos exhibited an embryonic lethal phenotype between 13.5 and 16.5 dpc because of severe abnormalities in liver morphogenesis, hypertrophy of blood vessels, and inability of lung mesenchyme to form peripheral pulmonary capillaries (Krupczak-Hollis et al, 2004; Kim et al, 2005a). Overall developmental defects in our Foxm1 Ϫ/Ϫ embryos were more severe compared to the previously reported Foxm1 Ϫ/Ϫneo mouse line, which contains a targeted insertion of PGK-Neo into Foxm1 gene locus without deleting any of the coding sequences (Korver et al, 1998). This includes a complete embryonic lethality, earlier thinning of myocardium, and dilation of the heart chambers (Krupczak-Hollis et al, 2004; this report).…”

“…Previous studies described the generation of Foxm1 Ϫ/Ϫneo mouse line that contained a targeted insertion of PGK-neomycin cassette into the third exon of Foxm1 gene without deleting any of the coding sequences (Korver et al, 1998). 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.…”

“…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).…”

FoxM1 is a downstream target and marker of HER2 overexpression in breast cancer

“…Moreover, FoxM1 exhibits cell cycledependent expression, which increases at the beginning of S-phase, and peaks in G2-and M-phases (16). Consistent with FoxM1 being involved in cell cycle control, knock-out mice are embryonic leathal and display abnormalities in the heart and liver, with many cells exhibiting polyploidy (17). Moreover, FoxM1 is induced in liver regeneration and tissue repair mouse models, which correlates with expression of numerous mitotic promoting genes (18)(19)(20).…”

Interaction of the fork head domain transcription factor MPP2 with the human papilloma virus 16 E7 protein: enhancement of transformation and transactivation

“…More recently the MPP2 gene was disrupted in mice and the analysis of MPP2 7/7 animals revealed a defect in the developing myocardium (Korver et al, 1998). This alteration is the likely reason for the observed neonatal lethality.…”