AbstractOligodendrocyte function is central to the maintenance of the normal nervous system in health and disease. In particular, process formation and the generation of large sheets of myelin are important components of their biological properties. We have investigated the role of Mayven, a recently identified member of the kelch family of proteins, in process extension in oligodendrocyte‐lineage cells. The kelch superfamily consists of a large number of structurally diverse proteins characterized by the presence of a kelch‐repeat domain. Other members of this family associate with the actin cytoskeleton and regulate process length. Mayven is expressed predominantly in the CNS, has six kelch repeats, and is an actin‐binding protein, associating with actin through its kelch‐repeat domain. We have cloned rat Mayven and examined its role in the oligodendrocyte lineage by using RT‐PCR, RNA interference, and a truncated, dominant‐negative myc‐tagged Mayven. Oligodendrocyte precursors treated with siRNA directed to Mayven have reduced process length, but there was no change in migration or expression of differentiation markers. Immunocytochemistry demonstrated that Mayven associated with F‐actin at cell tips. Finally, overexpression of truncated Mayven lacking the SH3 ligand binding domain in oligodendrocyte‐lineage cells resulted in shorter process formation, which was augmented when the cells were plated on laminin and fibronectin. These data suggest a role for Mayven in oligodendrocyte precursor cell process formation. © 2005 Wiley‐Liss, Inc.