Tep, C., Kim, M.L., Opincariu, L.I., Limpert, A.S., Chan, J.R., Appel, B., Carter, B.D., and Yoon, S.O. (2012) Brain-derived neurotrophic factor (BDNF) induces polarized signaling of small GTPase (Rac1) at the onset of Schwann cell myelination through partitioning-defective 3 (Par3). The Journal of biological chemistry. 287(2):1600-8.
Brain-derived neurotrophic factor (BDNF) was shown to play a role in Schwann cell myelination by recruiting Par3 to exon-glial interface, but the underlying mechanism
has remained unclear. Here we report that Par3 regulates Rac1 activation by BDNF, but not by NRG1-Type III in Schwann cells,
although both ligands activate Rac1 in vivo. During development, active Rac1 signaling is localized in a polarized manner
to axon-glial interface in Schwann cells. Knockdown of p75 and Par3 individually inhibits Rac1 activation, while constitutive
activation of Rac1 disturbs the polarized activation of Rac1 in vivo. Polarized Rac1 activation is necessary for myelination
as Par3 knockdown attenuates myelination in mouse sciatic nerves as well as in zebrafish. Specifically, Par3 knockdown in
zebrafish disrupts proper alignment between the axon and Schwann cells without perturbing Schwann cell migration, suggesting
that localized Rac1 activation at the axon-glial interface helps identifying the initial wrapping sites. We therefore conclude
that polarized activation of Rac1 activation is critical for myelination.