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Title: Investigating the 11q23.1 colorectal cancer risk locus
Author: Osborn, Ruby Tamara
ISNI:       0000 0004 7969 1624
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2019
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Colorectal cancer (CRC) is the fourth most common cancer in the UK and the second highest cause of cancer deaths. It is a complex disease with multiple environmental and genetic factors. Some risk genes have a low frequency of the risk allele in the population, but have a high effect, and have been well studied. Others are more common but have a much smaller effect; many of these are still being identified and characterised. The 11q23.1 locus was linked to CRC risk by a genome-wide association study, via the single nucleotide polymorphism rs3802842. Subsequent expression analysis on human colonic tissue revealed the risk allele of rs3802842 is correlated with lower expression of three adjacent genes: C11orf53, C11orf92 and C11orf93. C11orf53 and C11orf93 are protein coding, while C11orf92 is non-coding. All three are of unknown function. This locus is not associated with risk of cancer in any other tissue, but has been linked to colitis-associated- CRC in mice. To investigate these genes and their role in CRC, I have examined their localisation in intestinal tissue in humans and mice. I have created a knockout mouse model to study the effects of the loss of the genes on development and CRC induction, and used ex-vivo systems for further functional assays. The three genes have distinct transcript patterns along the length of the intestines, which are consistent between humans and mice. These patterns do not indicate they are specific to either stem cells or differentiated cells, although all genes show higher expression in the base of the crypt than the top. There are several significant differences in transcript level and distribution in the intestinal tissue of an established mouse CRC-susceptible background (ApcMin/+) compared to wild type tissue. Previous work by Claire Smillie and evidence that I have gathered using protein localisation indicate that at least one of the genes in this locus may play a role in the endoplasmic reticulum. The knockout mouse model created carries a 20kb deletion, spanning the last two thirds of C11orf53, all of C11orf92, and the first third of C11orf93. C11orf-/- occur at lower frequency than expected, and show around 50% survival in the week following weaning. Tissue staining in the intestines shows reduced staining of mucins secreted by goblet cells in C11orf-/- mice compared to C11orf+/+ mice. Global transcript expression analysis on intestinal tissue shows many immune system-related genes have altered expression between the genotypes, while blood panels show that C11orf-/- mice have low red and white blood cells. However, no obvious CRC phenotype has been observed in aged mice, or when crossed onto the ApcMin/+ susceptible background, or via chemical induction. Ex-vivo analysis of the knockout mice has utilised the culture of cell lines and intestinal organoids. Cell lines showed no differences in cell proliferation or migration between the genotypes. However C11orf-/- organoids did have reduced budding compared to C11orf+/+ organoids, a phenotype that is linked to defective intestinal homeostasis. In summary, I have created a mouse model deleting the 11q23.1 CRC risk locus. Deletion of these genes has not caused CRC to develop, but there is evidence of alteration in the intestinal, immune and blood systems, and the model should greatly aid in further understanding the functional role of these genes and their precise role in CRC risk. I hypothesise that the genes play a role in the endoplasmic reticulum, and disruption of these genes alters secretion, affecting goblet cells, the Wnt signalling pathway and the immune system.
Supervisor: Farrington, Susan ; Arends, Mark Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: colorectal cancer ; genetic factors ; C11orf53 ; C11orf92 ; C11orf93 ; 11q23.1 locus ; transcript level ; mouse model ; Wnt signalling pathway