Ongoing block of Schwann cell differentiation and deployment in dystrophic mouse spinal roots

In the spinal roots of dystrophic mice, there are bundles of unensheathed axons and two populations of axon-associated cells: the typical Schwann cells of myelinated fibers and 'uncommitted' cells at the margin of the bundles. Because these 'uncommitted' cells continue to divide in adult animals but fail to ensheath the axons they appose, they can be labelled with tritiated thymidine. In the present experiments, we show that these cells may differentiate into typical Schwann cells of myelinated or unmyelinated fibers when spinal roots from [3H]thymidine-labelled dystrophic mice are grafted into the sciatic nerves of non-dystrophic animals. Thus, this study demonstrates that the 'uncommitted' cells of dystrophic spinal roots are undifferentiated Schwann cells whose differentiation in the intact spinal roots is continuously prevented by some unknown mechanism.