The last set of slides of TSC2 function illustrates
an intrinsic regulatory mechanism for stem cells,
in this case, for growth and division.
The other intrinsic mechanisms that regulate asymmetry,
renewal, or apoptosis are being pursued by many different laboratories.
In the next set of slides, we're going to discuss how short-range interaction
with surrounding cells might regulate stem cell division.
Some insights of how stem cells interact with immediate environment,
usually called a niche, came from our earlier study
using different tissue damaging agents.
In the case of dextran sulfate sodium, or DSS,
it is a widely used chemical to induce
inflammatory bowel diseases
in mammalian experimental systems,
like a mouse or rat.
Dextran sulfate sodium is a synthetic polysaccharide
that has multiple positive charges.
Feeding DSS to animals can cause injury
that is compounded by the presence of commensal bacteria,
inflammation, cytokine production, and lymphocyte attractions
that cause serious tissue damage after inflammation.
It is a widely used model to study human ulcerative colitis.
Feeding of DSS to fruit flies, as shown in the lower panel,
can kill flies within days, depending on dosage that we used.
At early time points of day 1 and 2 and 3,
after feeding DSS,
we could already detect very highly increased mitotic activity
inside the drosophila midgut.