Unknown,Transcriptomics,Genomics,Proteomics

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Transcriptome changes following loss of Apc in the intestine

ABSTRACT: Nearly all colorectal cancers have dysregulated Wnt signalling, predominantly through the mutation of the Apc (Adenomatous Polyposis Coli) gene. Therefore it is of vital importance to elucidate the key Wnt target genes in intestinal cells in vivo. We have used a novel inducible cre-lox based murine system (designated ApcFlox) to investigate the consequences of perturbation of Wnt signalling following inactivation of Apc in vivo within 100% of the intestinal epithelium. We have employed microarray analysis at 3 time points within our ApcFlox system (Day 3 prior to the onset of phenotype, day 4 the establishment of the phenotype and day 5 gross phenotype of altered proliferation, differentiation and migration) and from adenomas arising in the ApcMin/+ background allowing us characterise Wnt/beta-catenin target genes based on their expression profiles during different stages of intestinal tumourigenesis. Furthermore, we have employed microarray analysis using livers from our ApcFlox system and have demonstrated that there is very little overlap in the Wnt target genes induced by Apc loss in the liver and the intestine. More importantly, we have been able to determine a novel set of putative Wnt/beta-catenin target genes which are upregulated at both early and late stages of tumourigenesis in the intestine and may represent novel therapeutic targets in colon cancer. Samples were collected from Genetcially modified mice of the genotypes indicated on the sample records. Where appropriate, gene recombination was induced using IP administration of beta-napthoflavone. Cohorts of samples were used to compare the affects of APC loss in the small intestine at three time points (and compared to matched control samples in which the gene was not recombined). Furthermore, these samples were compared to colonic polyps (and normal colon) taken from the Apcmin Mouse.

ORGANISM(S): Mus musculus

SUBMITTER: Karen Reed

PROVIDER: E-GEOD-65461 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Background: Wnt signaling maintains the undifferentiated state of intestinal crypt progenitor cells by inducing the formation of nuclear TCF4/beta-catenin complexes. In colorectal cancer, activating mutations in Wnt pathway components cause inappropriate activation of TCF4/beta-catenin -driven transcription. Despite the passage of a decade after the discovery of TCF4 and beta-catenin as the molecular effectors of the Wnt signal, few transcriptional activators essential and unique to the regulation of this transcription program have been found. Methodology/Principal Findings: Using proteomics, we identified the leukemia-associated Mllt10/Af10 and the methyltransferase Dot1l, as Tcf4/beta-catenin interactors in mouse small intestinal crypts. Mllt10/Af10-Dot1l, essential for transcription elongation, are recruited to Wnt target genes in a beta-catenin -dependent manner, resulting in H3K79 methylation over their coding regions in vivo in proliferative crypts of mouse small intestine, in colorectal cancer and Wnt-inducible HEK293T cells. Depletion of MLLT10/AF10 in colorectal cancer and Wnt-inducible HEK293T cells followed by expression array analysis identifies MLLT10/AF10 and DOT1L as essential activators dedicated to Wnt target gene regulation. In contrast, previously published b-catenin coactivators p300 and beta-catenin displayed a more pleiotropic target gene expression profile controlling Wnt and other pathways. tcf4, mllt10/af10 and dot1l are co-expressed in Wnt-driven tissues in zebrafish and essential for Wnt-reporter activity. Intestinal differentiation defects in apc-mutant zebrafish can be rescued by depletion of Mllt10 and Dot1l, establishing these genes as activators downstream of Apc in Wnt target gene activation in vivo. Morpholino-depletion of mllt10/af10-dot1l in zebrafish results in defects in intestinal homeostasis and a significant reduction in the in vivo expression of direct Wnt target genes and in the number of proliferative intestinal epithelial cells. Conclusions/Significance: We conclude that Mllt10/Af10-Dot1l are essential, dedicated activators of Wnt-dependent transcription, critical for maintenance of intestinal proliferation and homeostasis. The methyltransferase Dot1l may present an attractive candidate for drug targeting in colorectal cancer. 6 samples for Ls174T cells: si-b-catenin against si-control and dyeswap of it, si-control, si-MLLT10, si-BRG1 and si-P300 are hybridized against common reference RNA; 6 samples of HEK293T cells: Wnt3A or control medium (CM) induction for 9 hours, si-MLLT10, si-DOT1L, si-BRG1 and si-P300 upon 9 hour Wnt3A induction are all hybridized against common reference RNA

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Transcriptome changes following loss of Apc in the intestine

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