Temporal regulation of enhancer function in intestinal epithelium: a role for Onecut factors

Emerging role of ONECUT2 in tumors

One cut domain family member 2 (ONECUT2), also termed OC-2, is a newly discovered member of the ONECUT transcription factor family. As a transcription factor, ONECUT2 can widely regulate protein expression associated with cell proliferation, migration, adhesion, differentiation and cell material metabolism. Recent studies have revealed that ONECUT2 is associated with tumor cell proliferation, angiogenesis and metastasis; it is also associated with epithelial-mesenchymal transition in cancer cells. The present review examines the distribution and expression of ONECUT2 in a variety of tumors, its oncogenic role in tumor progression and the possible mechanisms of regulation. Given the emerging role of ONECUT2 in the development and progression of tumors, ONECUT2 might be a promising target for tumor therapy.

Unique Gene Expression Signatures in the Intestinal Mucosa and Organoids Derived from Germ-Free and Monoassociated Mice

Commensal microbiota contribute to gut homeostasis by inducing transcription of mucosal genes. Analysis of the impact of various microbiota on intestinal tissue provides an important insight into the function of this organ. We used cDNA microarrays to determine the gene expression signature of mucosa isolated from the small intestine and colon of germ-free (GF) mice and animals monoassociated with two E. coli strains. The results were compared to the expression data obtained in conventionally reared (CR) mice. In addition, we analyzed gene expression in colon organoids derived from CR, GF, and monoassociated animals. The analysis revealed that the complete absence of intestinal microbiota mainly affected the mucosal immune system, which was not restored upon monoassociation. The most important expression changes observed in the colon mucosa indicated alterations in adipose tissue and lipid metabolism. In the comparison of differentially expressed genes in the mucosa or organoids obtained from GF and CR mice, only six genes were common for both types of samples. The results show that the increased expression of the angiopoietin-like 4 (Angptl4) gene encoding a secreted regulator of lipid metabolism indicates the GF status.

Cross Talk Between GH-Regulated Transcription Factors HNF6 and CUX2 in Adult Mouse Liver

Hepatocyte-enriched nuclear factor (HNF)6 and CUX2 are GH and STAT5-regulated homeobox transcription factors. CUX2 shows female-specific expression and contributes to liver sex differences by repressing many male-biased genes and inducing many female-biased genes, whereas HNF6 is expressed at similar levels in male and female liver. In cell-based transfection studies, CUX2 inhibited HNF6 transcriptional regulation of the sex-specific gene promoters CYP2C11 and CYP2C12, blocking HNF6 repression of CYP2C11 and HNF6 activation of CYP2C12. These inhibitory actions of CUX2 can be explained by competition for HNF6 DNA binding, as demonstrated by in vitro EMSA analysis and validated in vivo by global analysis of the HNF6 cistrome. Approximately 40 000 HNF6-binding sites were identified in mouse liver chromatin, including several thousand sites showing significant sex differences in HNF6 binding. These sex-biased HNF6-binding sites showed strong enrichment for correspondingly sex-biased DNase hypersensitive sites and for proximity to genes showing local sex-biased chromatin marks and a corresponding sex-biased expression. Further, approximately 90% of the genome-wide binding sites for CUX2 were also bound by HNF6. These HNF6/CUX2 common binding sites were enriched for genomic regions more accessible in male than in female mouse liver chromatin and showed strongest enrichment for male-biased genes, suggesting CUX2 displacement of HNF6 as a mechanism to explain the observed CUX2 repression of male-biased genes in female liver. HNF6 binding was sex independent at a majority of its binding sites, and HNF6 peaks were frequently associated with cobinding by multiple other liver transcription factors, consistent with HNF6 playing a global regulatory role in both male and female liver.

Onecut-2 knockout mice fail to thrive during early postnatal period and have altered patterns of gene expression in small intestine

Ablation of the mouse genes for Onecut-2 and Onecut-3 was reported previously, but characterization of the resulting knockout mice was focused on in utero development, principally embryonic development of liver and pancreas. Here we examined postnatal development of these Onecut knockout mice, especially the critical period before weaning. Onecut-3 knockout mice develop normally during this period. However, Onecut-2 knockout mice fail to thrive, lagging behind their littermates in size and weight. By postnatal day (d)19, they are consistently 25-30% smaller. Onecut-2 knockout mice also have a much higher level of mortality before weaning, with only approximately 70% survival. Interestingly, Onecut-2 knockout mice that are heterozygous for the Onecut-3 knockout allele are diminished even further in their ability to thrive. They are approximately 50-60% as large as their normal-sized littermates at d19, and less than half of these mice survive to weaning. As reported previously, the Onecut-2/Onecut-3 double knockout is a perinatal lethal. Microarray technology was used to determine the effect of Onecut-2 ablation on gene expression in duodenum, whose epithelium has among the highest levels of Onecut-2. A subset of intestinally expressed genes showed dramatically altered patterns of expression. Many of these genes encode proteins associated with the epithelial membrane, including many involved in transport and metabolism. Previously, we reported that Onecut-2 was critical to temporal regulation of the adenosine deaminase gene in duodenum. Many of the genes with altered patterns of expression in Onecut-2 knockout mouse duodenum displayed changes in the timing of gene expression.