After identifying genes active in cNeoblasts, Wagner irradiated the planarians, leaving a single surviving cNeoblast in each planarian. Left alone, each cNeoblast can form colonies of new cells at very specific rates of differentiation and stem cell renewal.
The researchers knocked down each of the active genes, one per planarian, and observed how the surviving cNeoblasts responded. By comparing the rate of differentiation and stem cell renewal to that of normal cNeoblasts, they could determine the role of each gene. Thus, if a colony containing a certain knocked down gene were observed to have fewer stem cells than the controls, it could be concluded that gene in question plays a role in the process of stem cell renewal. And if the colony had fewer differentiated cells than normal, the knocked down gene could be associated with differentiation.
"Because it's a quantitative method, we can now precisely measure the role of each gene in different aspects of stem cell function," says Wagner. "Being able to measure stem cell activity with a colony is a great improvement over methods that existed before, which were much more indirect."
In total, Wagner identified 10 genes impacting cNeoblast renewal, and two genes with roles in both renewal and differentiation. According to Wagner, three of the stem cell renewal genes are particularly intriguing because they code for proteins that are similar to components of Polycomb Repressive Complex 2 (PRC2), known to regulate stem cell biology in mammalian embryonic stem cells and in other stem cell systems.
"It's interesting because it suggests a parallel between how stem cells operate in planarians and in mammals. For example, there might be similarities between how cNeoblasts and embryonic stem cells function and maintain stemness at the molecular level," he says.
|Contact: Nicole Giese Rura|
Whitehead Institute for Biomedical Research