In vitro manipulation of preimplantation mammalian embryos can influence differentiation and growth at later stages of development. In the mouse, culture of embryonic stem (ES) cells affects their totipotency and may give rise to fetal abnormalities. To investigate whether this is associated with epigenetic alterations in imprinted genes, we analysed two maternally expressed genes (Igf2r, H19) and two paternally expressed genes (Igf2, U2af1-rs1) in ES cells and in completely ES cell-derived fetuses. Altered allelic methylation patterns were detected in all four genes, and these were consistently associated with allelic changes in gene expression. All the methylation changes that had arisen in the ES cells persisted on in vivo differentiation to fetal stages. Alterations included loss of methylation with biallelic expression of U2af1-rs1, maternal methylation and predominantly maternal expression of Igf2, and biallelic methylation and expression of Igf2r. In many of the ES fetuses, the levels of H19 expression were strongly reduced, and this biallelic repression was associated with biallellic methylation of the H19 upstream region. Surprisingly, biallelic H19 repression was not associated with equal levels of Igf2 expression from both parental chromosomes, but rather with a strong activation of the maternal Igf2 allele. ES fetuses derived from two of the four ES lines appeared developmentally compromised, with polyhydramnios, poor mandible development and interstitial bleeding and, in chimeric fetuses, the degree of chimerism correlated with increased fetal mass. Our study establishes a model for how early embryonic epigenetic alterations in imprinted genes persist to later developmental stages, and are associated with aberrant phenotypes.

Enterotoxigenic Bacteroides fragilis (ETBF) is a toxin-producing bacteria thought to possibly promote colorectal carcinogenesis by modulating the mucosal immune response and inducing epithelial cell changes. Here, we aim to examine the association of colonic mucosal colonization with ETBF and the presence of a range of lesions on the colonic neoplastic spectrum. Mucosal tissue from up to four different colonic sites was obtained from a consecutive series of 150 patients referred for colonoscopy. The presence and relative abundance of the B. fragilis toxin gene (bft) in each tissue sample was determined using quantitative PCR, and associations with clinicopathological characteristics were analysed. We found a high concordance of ETBF between different colonic sites (86%). Univariate analysis showed statistically significant associations between ETBF positivity and the presence of low-grade dysplasia (LGD), tubular adenomas (TA), and serrated polyps (P-values of 0.007, 0.027, and 0.007, respectively). A higher relative abundance of ETBF was significantly associated with LGD and TA (P-values of < 0.0001 and 0.025, respectively). Increased ETBF positivity and abundance was also associated with left-sided biopsies, compared to those from the right side of the colon. Our results showing association of ETBF positivity and increased abundance with early-stage carcinogenic lesions underlines its importance in the development of colorectal cancer, and we suggest that detection of ETBF may be a potential marker of early colorectal carcinogenesis.

The mouse H19 gene is expressed from the maternal chromosome exclusively. A 2-kb region at 2 to 4 kb upstream ofH19 is paternally methylated throughout development, and these sequences are necessary for the imprinted expression of bothH19 and the 5′-neighboring Igf2 gene. In particular, on the maternal chromosome this element appears to insulate the Igf2 gene from enhancers located downstream ofH19. We analyzed the chromatin organization of this element by assaying its sensitivity to nucleases in nuclei. Six DNase I hypersensitive sites (HS sites) were detected on the unmethylated maternal chromosome exclusively, the two most prominent of which mapped 2.25 and 2.75 kb 5′ to the H19 transcription initiation site. Five of the maternal HS sites were present in expressing and nonexpressing tissues and in embryonic stem (ES) cells. They seem, therefore, to reflect the maternal origin of the chromosome rather than the expression of H19. A sixth maternal HS site, at 3.45 kb upstream of H19, was detected in ES cells only. The nucleosomal organization of this element was analyzed in tissues and ES cells by micrococcal nuclease digestion. Specifically on the maternal chromosome, an unusual and strong banding pattern was obtained, suggestive of a nonnucleosomal organization. From our studies, it appears that the unusual chromatin organization with the presence of HS sites (maternal chromosome) and DNA methylation (paternal chromosome) in this element are mutually exclusive and reflect alternate epigenetic states. In addition, our data suggest that nonhistone proteins are associated with the maternal chromosome and that these might be involved in its boundary function.

The DUTT1 gene is located on human chromosome 3, band p12, within a region of nested homozygous deletions in breast and lung tumors. It is therefore a candidate tumor suppressor gene in humans and is the homologue (ROBO1) of the Drosophila axonal guidance receptor gene, Roundabout. We have shown previously that mice with a targeted homozygous deletion within the Dutt1/Robo1 gene generally die at birth due to incomplete lung development: survivors die within the first year of life with epithelial bronchial hyperplasia as a common feature. Because Dutt1/Robo1 heterozygous mice develop normally, we have determined their tumor susceptibility. Mice with a targeted deletion within one Dutt1/Robo1 allele spontaneously develop lymphomas and carcinomas in their second year of life with a 3-fold increase in incidence compared with controls: invasive lung adenocarcinomas are by far the predominant carcinoma. In addition to the mutant allele, loss of heterozygosity analysis indicates that these tumors retain the structurally normal allele but with substantial methylation of the gene's promoter. Substantial reduction of Dutt1/Robo1 protein expression in tumors is observed by Western blotting and immunohistochemistry. This suggests that Dutt1/Robo1 is a classic tumor suppressor gene requiring inactivation of both alleles to elicit tumorigenesis in these mice

Background and aims: Transforming growth factor β (TGF-β) is frequently involved in gastrointestinal carcinogenesis although its contribution to oesophageal adenocarcinoma (AC) and its precursor Barrett’s oesophageal epithelium (BE) metaplasia are unclear. Methods: Expression of TGF-β signalling components was assessed by reverse transcription-polymerase chain reaction (PCR), western blot, and immunohistochemistry in oesophageal endoscopic biopsies and cell lines. Genomic alterations in SMAD4 were characterised by fluorescence in situ hybridisation, methylation specific PCR, and sequencing. Functional integrity of TGF-β signalling was assessed by characterisation of p21 and proliferation status. Smad4 negative BIC-1 cells were transiently transfected with smad4 and TGF-β responsiveness evaluated. Results: smad4 mRNA expression was progressively reduced in the metaplasia-dysplasia-adenocarcinoma sequence (p80% of BE and AC. TGF-β failed to inhibit proliferation in 5/8 oesophageal cell lines. In BIC-1, the antiproliferative response was restored following transient transfection of smad4 cDNA. Conclusions: In BE carcinogenesis, downregulation of Smad4 occurs due to several different mechanisms, including methylation, deletion, and protein modification. Frequent alterations in TGF-β signalling lead to a functionally significant impairment of TGF-β mediated growth suppression.