I'd like to understand better how stem cells produce fully differentiated cells via progenitor cells. I assume the following:
Only cells that are not fully differentiated do divide at all.
When a stem cell divides (at least) one copy remains a stem cell (and remains at its place), the other one starts to differentiate and to travel away.
Between the stem cell and the fully differentiated cell there may be one or a few progenitor cells.
My questions are:
How many cell generations are there between the stem cell and the fully differentiated cell?
Any answer from "zero" or "one" (with one progenitor cell inbetween) to "quite a few" seems possible, but maybe "zero generations" do never occur, i.e. no copy of a stem cell fully differentiates at once, i.e. without an intermediate progenitor cell.
How many cell generations are there between the stem cell and the last progenitor cell in the lineage from stem cell to fully differentiated cell?
How many cell generations are there between the last progenitor cell and the fully differentiated cell?
By definition there should be zero, because when there is another not fully differentiated cell between them, then this would be another progenitor cell.
The questions are for somehow typical numbers (of generations), but the answers may depend on the tissue (resp. the type of the stem cell), so it would be interesting to know how strongly (this depends).