Persistent multiplication of axon-associated cells in the spinal roots of dystrophic mice.

Axons which lack Schwann cells characterize the spinal roots of dystrophic mice. In these nerves, two types of cells are associated with large axons-typical Schwann cells which ensheath and myelinate individual axons and "uncommitted" cells which closely contact some axons but do not unsheath them normally. Although neonatal Schwann cell multiplication in dystrophic spinal roots is less than normal, the "uncommitted" cells continue to multiply in adult animals. Thus, these cells are presumably responsive to the mitogenic stimulus of axons, but are unable to extend radially and longitudinally to form a myelin sheath. This disorder of axon-sheath cell interactions could be due to an intrinsic abnormality of Schwann cells or a failure of the mechanisms whereby axons induce Schwann cell differentiation.