Molecular teamwork decoded
Earlier research had shown that marking by Rnf43 in itself was not enough to break down the Wnt receptor. Like most receptors, the Wnt receptor is located in the membrane surrounding the cell, its plasma membrane. For marking by Rnf43 to lead to its breakdown, the receptor would first have to be absorbed into the cell. “This is where our research project comes in,” says Colozza. “Using biochemical assays and mass spectrometry, we were able to analyse which proteins interact with Rnf43.” Colozza identified a gene called Daam as the missing link. “It ensures that the Wnt receptor is incorporated into the cell. This means that Daam and Rnf43 work in tandem to dampen the Wnt signalling pathway,” the expert explains.
Effects investigated in intestinal organoids
To translate the discovery from the molecular level to the organ level, one of the methods Colozza used were intestinal organoids. These three-dimensional structures are grown as cell cultures from adult stem cells and have a structure and properties similar to those of intestinal mucosa. Colozza used them to determine that Daam is essential for the differentiation of intestinal stem cells to form so-called Paneth cells. These cells secrete substances that stimulate cell division in intestinal stem cells. “Daam acts as a switch,” the scientist explains. “When it is switched on, the stem cell differentiates to form a Paneth cell. When it is switched off, the cell takes another path.”
More Paneth cells in colorectal cancer
The link between the results at the molecular level and the development of Paneth cells lends the project additional importance. This is because one of the functions of Paneth cells is to regulate ambient conditions in the crypts. Since Paneth cells stimulate stem cell division, their excessive prevalence can contribute to the development of cancer.
“Mouse models have been used to show that such tumours recede when the excessive proliferation of Paneth cells is genetically blocked,” Colozza explains. “Our research has delivered the first genetic proof that a component of the Wnt signalling pathway is directly involved in the development of this crucial type of cell.” This also puts a new goal within reach in the development of drugs against colorectal cancer.
Results enhance understanding of stem cells
“Our results demonstrate how stem cells make decisions,” says Colozza. That is a boon to science as such in his opinion. “While we know how to cultivate certain cells in the lab, we often lack the means to push them in a specific direction.” This is changing with increasing insight into genetic and molecular mechanisms. The identification of Daam is an important step towards being able to specifically stimulate the development of stem cells into particular types of cells.