An alternative stochastic model of generation of oligodendrocytes in cell culture

According to our previous model, oligodendrocyte - type 2 (O-2A) astrocyte progenitor cells become competent for differentiation in vitro after they c omplete a certain number of critical mitotic cycles. After attaining the co mpetency to differentiate, progenitor cells divide with fixed probability p in subsequent cycles. The number of critical cycles is random analysis of data suggests that it varies from zero to two. The present paper presents a n alternative model in which there are no critical cycles, and the probabil ity that a progenitor cell will divide again decreases gradually to a plate au value as the number of completed mitotic cycles increases. In particular all progenitor cells have the ability to differentiate from the time of pl ating. The Kiefer-Wolfowitz procedure is used to fit the new model to exper imental data on the clonal growth of purified O-2A progenitor cells obtaine d from the optic nerves of 7 day old rats. The new model is shown to fit th e experimental data well, indicating that it is not possible to determine w hether critical cycles exist on the basis of these experimental data. In co ntrast to the fit of the previous model, which suggested that the addition of thyroid hormone increased the limiting probability of differentiation as the number of mitotic cycles increases, the fit of the new model suggests that the addition of thyroid hormone has almost no effect oil the limiting probability of differentiation.