Mice Carrying a Hypomorphic Evi1 Allele Are Embryonic Viable but Exhibit Severe Congenital Heart Defects

Abstract

The ecotropic viral integration site 1 (Evi1) oncogenic transcription factor is one of a number of alternative transcripts encoded by the Mds1 and Evi1 complex locus (Mecom). Overexpression of Evi1 has been observed in a number of myeloid disorders and is associated with poor patient survival. It is also amplified and/or overexpressed in many epithelial cancers including nasopharyngeal carcinoma, ovarian carcinoma, ependymomas, and lung and colorectal cancers. Two murine knockout models have also demonstrated Evi1's critical role in the maintenance of hematopoietic stem cell renewal with its absence resulting in the death of mutant embryos due to hematopoietic failure. Here we characterize a novel mouse model (designated Evi1fl3) in which Evi1 exon 3, which carries the ATG start, is flanked by loxP sites. Unexpectedly, we found that germline deletion of exon3 produces a hypomorphic allele due to the use of an alternative ATG start site located in exon 4, resulting in a minor Evi1 N-terminal truncation and a block in expression of the Mds1-Evi1 fusion transcript. Evi1δex3/δex3 mutant embryos showed only a mild non-lethal hematopoietic phenotype and bone marrow failure was only observed in adult Vav-iCre/+, Evi1fl3/fl3 mice in which exon 3 was specifically deleted in the hematopoietic system. Evi1δex3/δex3 knockout pups are born in normal numbers but die during the perinatal period from congenital heart defects. Database searches identified 143 genes with similar mutant heart phenotypes as those observed in Evi1δex3/δex3 mutant pups. Interestingly, 42 of these congenital heart defect genes contain known Evi1-binding sites, and expression of 18 of these genes are also effected by Evi1 siRNA knockdown. These results show a potential functional involvement of Evi1 target genes in heart development and indicate that Evi1 is part of a transcriptional program that regulates cardiac development in addition to the development of blood.

SOX9 modulates the expression of key transcription factors required for heart valve development

“…Mecom-and Nfia-associated SOX9 peaks were upstream of the genes in putative enhancers, whereas the SOX9 peak for Junb was located within the promoter. Mecom has been shown to be expressed in the developing heart valves (Hoyt et al, 1997;Bard-Chapeau et al, 2014) but its exact role in the AV valves is not well understood. NFI factors have been shown to work together with SOX9 to regulate downstream target genes in other systems (Nagy et al, 2011;Kang et al, 2012) and Junb has a well-established role in regulating cell cycle.…”

“…TFs with the most reduced expression in Sox9 cKO valves were Twist1, Sox4 and Mecom. Similar to SOX9, these three TFs are highly expressed in the cardiac cushions and mutations in each of these factors cause major valve defects, resulting in embryonic fatality (Ya et al, 1998;Vincentz et al, 2008;Bard-Chapeau et al, 2014).…”

“…For example, TWIST1 has been shown to regulate Tbx20 (Lee and Yutzey, 2011) and TBX20 in turn has been shown to regulate LEF1 in the valve endocardial cells (Cai et al, 2013). EVI1 has been shown to regulate SOX4 and alters its expression (Bard-Chapeau et al, 2014), and EVI1 and SOX4 can collaborate together in myeloid leukemia (Boyd et al, 2006). This demonstrates that complex interactions occur at multiple levels in transcriptional regulation by SOX9 and suggests that the essential TFs are regulated in numerous ways to ensure proper valve formation.…”

The New Clinicopathologic and Molecular Findings in Myeloid Neoplasms With inv(3)(q21q26)/t(3;3)(q21;q26.2)

“…Studies of mice with homozygous deletion of EVI1 show death in utero, with defects in the development, expansion, maintenance, and differentiation of hematopoietic stem cells. 39,40 Defects in angiogenesis, 39 heart structure, 41 and vascularization 39,42 were also described. EVI1 exists as a single gene, or as part of a larger complex named MECOM, which stands for MDS1/EVI1 complex.…”

EVI1 Mediated Stimulation of 3T3-L1 Preadipocyte Differentiation Is CtBP Dependent

“…Those transcripts containing EVI1 encode transcription factors with multiple cys2his2 zinc finger DNA binding motifs [4] and are required for mammalian development [5]. EVI1 has been shown to contribute to a number of developmental programmes including maintenance of haemopoietic stem cells and various committed progenitor cells in haemopoiesis [6], neuroectodermal cell differentiation [7], nephrogenesis [8] and cardiac development [9].…”