Dynein/dynactin is necessary for anterograde transport of <i>Mbp</i> mRNA in oligodendrocytes and for myelination in vivo.

Abstract

Oligodendrocytes in the central nervous system produce myelin, a lipid-rich, multilamellar sheath that surrounds axons and promotes the rapid propagation of action potentials. A critical component of myelin is myelin basic protein (MBP), expression of which requires anterograde mRNA transport followed by local translation at the developing myelin sheath. Although the anterograde motor kinesin KIF1B is involved in <i>mbp</i> mRNA transport in zebrafish, it is not entirely clear how <i>mbp</i> transport is regulated. From a forward genetic screen for myelination defects in zebrafish, we identified a mutation in <i>actr10</i>, which encodes the Arp11 subunit of dynactin, a critical activator of the retrograde motor dynein. Both the <i>actr10</i> mutation and pharmacological dynein inhibition in zebrafish result in failure to properly distribute <i>mbp</i> mRNA in oligodendrocytes, indicating a paradoxical role for the retrograde dynein/dynactin complex in anterograde <i>mbp</i> mRNA transport. To address the molecular mechanism underlying this observation, we biochemically isolated reporter-tagged <i>Mbp</i> mRNA granules from primary cultured mammalian oligodendrocytes to show that they indeed associate with the retrograde motor complex. Next, we used live-cell imaging to show that acute pharmacological dynein inhibition quickly arrests <i>Mbp</i> mRNA transport in both directions. Chronic pharmacological dynein inhibition also abrogates <i>Mbp</i> mRNA distribution and dramatically decreases MBP protein levels. Thus, these cell culture and whole animal studies demonstrate a role for the retrograde dynein/dynactin motor complex in anterograde <i>mbp</i> mRNA transport and myelination in vivo.