RT Journal Article SR Electronic T1 A Selective Glial Barrier at Motor Axon Exit Points Prevents Oligodendrocyte Migration from the Spinal Cord JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 15187 OP 15194 DO 10.1523/JNEUROSCI.4193-09.2009 VO 29 IS 48 A1 Sarah Kucenas A1 Wen-Der Wang A1 Ela W. Knapik A1 Bruce Appel YR 2009 UL http://www.jneurosci.org/content/29/48/15187.abstract AB Nerve roots have specialized transition zones that permit axon extension but limit cell movement between the CNS and PNS. Boundary cap cells prevent motor neuron soma from following their axons into the periphery, thereby contributing to a selective barrier. Transition zones also restrict movement of glial cells. Consequently, axons that cross the CNS–PNS interface are insulated by central and peripheral myelin. The mechanisms that prevent the migratory progenitors of oligodendrocytes and Schwann cells, the myelinating cells of the CNS and PNS, respectively, from crossing transition zones are not known. Here, we show that interactions between myelinating glial cells prevent their movements across the interface. Using in vivo time-lapse imaging in zebrafish we found that, in the absence of Schwann cells, oligodendrocyte progenitors cross ventral root transition zones and myelinate motor axons. These studies reveal that distinct mechanisms regulate the movement of axons, neurons, and glial cells across the CNS–PNS interface.