Cells were cultured for one week until they started to dedifferentiate and divide.
From the nature.com
Myoblasts that do not form muscle fibers dedifferentiate back into satellite cells.
From the en.wikipedia.org
Sure enough, Pajcini and Pomerantz found that blocking the expression of both Rb and ARF allowed individual myocytes isolated from mouse muscle to dedifferentiate and begin dividing.