The effects of aberrant Wnt signalling on the murine intestinal stem cell compartment

Colorectal cancer is the 2nd most common cause of death by cancer in the UK, but it is treatable if diagnosed early. In order to increase the likelihood of early diagnosis, more must be understood about the early stages of colorectal tumourigenesis. It is known that intestinal stem cells (ISCs) are the cells of origin of colorectal tumourigenesis, and that an expansion of undifferentiated cell types, akin to ISCs, is one of the earliest events in mouse models of tumourigenesis. This indicates the importance of the relationship between the ISC compartment and tumourigenesis. In order to understand how changes in the ISC compartment may be contributing to tumourigenesis, the ability to accurately quantify this compartment is essential. Currently, analysis of the ISC compartment relies on the analysis of gene expression levels of ISC markers. However, there is a great deal of controversy surrounding the majority of these markers and there is no evidence that alterations in expression levels of these markers results in a functional change in the ISC compartment. Here I present a novel method for assessing the ISC compartment based on a functional capacity of ISCs; the ability to form intestinal organoids in culture. This new method uses organoid formation efficiency as a readout of changes in the ISC compartment, and can be used in conjunction with traditional methods of ISC marker expression to understand the relationship between expression of ISC markers and ISC functionality. I have used this method to further analyse the intestinal phenotype of a range of mouse models of colorectal cancer based on gene deletion of Apc, Cited1, Apc2, Pten and Pml. These experiments have shown that organoid formation efficiency can be a useful method for assessing the ISC compartment, although changes within this compartment may not be accurately predictive of tumourigenesis.