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Transcription profiling by array of Apc-deficient proximal colonic epithelium upon Msx1 transcription factor depletion

ABSTRACT: The first step in the development of human colorectal cancer (CRC) is the aberrant hyperactivation of the Wnt signaling pathway, predominantly caused by inactivating mutations in the adenomatous polyposis coli (APC) gene which encodes an essential tumor suppressor. In order to identify genes affected by Apc loss, expression profiling of intestinal epithelium isolated from mice harboring the conditional allele of the gene was performed. The gene encoding transcriptional factor msh homeobox 1 (Msx1) displayed robust upregulation upon Apc inactivation. To characterize the gene signature in colon upon Msx1 depletion, colonic epithelium from mice harboring conditional alleles of Apc and Msx1 was isolated and the gene expression profile was compared with control mice harboring the conditional allele of Apc only.

REANALYSIS of: E-MTAB-6909

ORGANISM(S): Mus musculus

PROVIDER: E-MTAB-6909 | ExpressionAtlas | 2018-09-17

REPOSITORIES: ExpressionAtlas

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Project description:We tamoxifen treated 8-12 week old mice that had floxed alleles of the following: 1) both Apc alleles (giving rise to Apc truncation/inactivation); 2) both Cdx2 alleles (giving rise to Cdx2 inactivation; 3) one Braf allele, that upon Cre-mediated recombination gives a Braf V600E mutant allele (details below), and 4) the combination of both the Cdx2 alleles and the BrafV600E allele. All four of those groups also had a CDX2P-CreERT2 transgene that expresses Cre recombinase fused to a tamoxifen-regulated fragment of the estrogen receptor ligand binding domain. CreERT2 expression occurs only in tissues where the Cdx2 gene is expressed, which is almost exclusively in adult mouse cecum and colon epithelium. A fifth group of mice had the floxed Cdx2 alleles, but no CDX2P-CreERT2 gene. Treating the mice having CDX2P-CreERT2 with tamoxifen permits the Cre recombinase to enter the cell nucleus and recombine the Apc, Braf, and/or Cdx2 alleles containing loxP sequence elements. Mice were treated with intraperitoneal injection of tamoxifen dissolved in corn oil. Three mice per group were used. The control mice did not develop tumors or any morphological or histological changes in their epithelium, but their colons were used to create the 3 control samples. To obtain the BrafV600E allele we used a genetically engineered mouse line previously described by Dankort et al. (Genes Dev 2007, 21:379-84) that can express the BrafV600E mutant protein following Cre-mediated recombination. The Braf(CA) (Braf-Cre-activated) allele mice carry a gene-targeted allele of Braf, where Braf sequences from exons 15-18 are present in the normal mouse Braf intron 14, followed by a mutated exon 15 (carrying the V600E mutation). The exon 15-18 sequence element is flanked by loxP sites. In the absence of Cre-mediated recombination, the Braf(CA) allele expresses a wild type Braf protein. Following Cre-mediated recombination, the Braf exon 15-18 element is removed, and the Braf(CA) allele then encodes the Braf V600E protein (from the introduced mutated exon 15). RNA was purified from tumor or normal tissue, and targets for Affymetrix arrays were synthesized from the mRNAs. We used Affymetrix Mouse Gene 2.1 ST arrays, which hold 41345 probe-sets, but we largely analyzed just those 25216 probe-sets that were mapped to Entrez gene IDs. Raw data was processed with the Robust Multi-array Average algorithm (RMA). Data is log2-transformed transcript abundance estimates. We fit a one-way ANOVA model to the five groups of samples. We supply a supplementary excel workbook that holds the same data as the data matrix file, but also holds the probe-set annotation at the time we analyzed the data, and some simple statistical calculations, which selects subsets of the probe-sets as differentially expressed between pairs of groups, as well as significant Cdx2-/- by Braf V600E interactions. It also gives the homologous human gene IDs we used for enrichment testing, which were 1-to-1 best homologs according to build 68 of NCBI's Homologene. A second supplementary sheet shows the data we enrichment tested after collapsing to distinct human homologs, joins of the results of tests with GSE4045 data and of tests with TCGA data to the mouse genes, and the intersections of selected genes in those data set with our gene selections in mouse. Consumers should consider obtaining more up-to-date probe-set annotation for the array platform. Overall design: Three colon tumor samples from 3 mice with conditional knockout of Apc, 3 colon tumors samples from 3 mice with conditional knockout of Cdx2, 3 colon tumor samples from 3 mice with conditional rearrangement of Braf to yield Braf V600E mutations, 3 colon tumor samples from 3 mice with both the Cdx2 knockout and the Braf V600E mutation, and 3 samples from the colons of 3 control mice (who had floxed Cdx2 alleles but no Cre recombinase transgene).