Functions of p130Cas in oligodendrocytes have yet to be described. Here we show that p130Cas is expressed during all stages of oligodendrocyte maturation in culture as well as in the oligodendrocyte precursor cell line Oli-neu. In oligodendroglial cells, p130Cas is phosphorylated by Fyn, coimmunoprecipitates with Fyn and co-localizes with Fyn at the leading edge of distal processes. Reduction of p130Cas by siRNA impairs cellular process outgrowth and thickness as well as migration of Oli-neu cells. Interestingly, prolonged reduction of p130Cas results in increased apoptosis in primary oligodendrocyte cultures causing a reduction in cell number. Our results demonstrate that oligodendroglial p130Cas contributes to the Fyn signalling pathway and affects morphological changes important for oligodendrocyte differentiation and the myelination process. The CNS consists of neurons and glial cells forming an efficient yet extremely complex network of interacting functional units. Specialized membrane extensions of oligodendrocytes elaborate the multilayered myelin sheath in the CNS. The cells undergo dramatic morphological changes during differentiation in vivo which can also be observed in vitro. OPCs migrate through the developing CNS and appear to scan the environment for appropriate axonal targets which are recognized and myelinated if certain prerequisites are met. Although a number of signals have been identified which seem to determine the movement of OPCs and the place, timing and rate of myelin formation, a detailed understanding of these mechanisms is still lacking. Myelin synthesis requires complex rearrangements of the oligodendroglial cellular architecture which need to be understood in detail to comprehend the cell biological basics of myelination. The nonreceptor Src-family tyrosine kinase Fyn was previously reported as a key signaling component in several cellular processes in oligodendrocytes that are AZD2281 abmole related to the myelination process. We investigated downstream targets of oligodendroglial Fyn kinase and identified p130Cas. In agreement with an analysis of developing mouse brain, we showed that p130Cas protein is present at early and late stages of oligodendrocyte differentiation in culture in which the cells express low levels of CNP and no detectable MOG, or high levels of CNP and MOG, respectively. p130Cas is the prototypical member of the Cas family of adaptor proteins which also includes NEDD9, EFS and CASS4. The structure of p130Cas consists of an Nterminal Src-homology 3 domain, a proline-rich domain, a substrate domain containing 15 YxxP motifs which are phosphorylated by Src family kinases, a four helix bundle serine-rich domain, and a C-terminal domain containing a bipartite Src binding domain. We confirm here that Fyn interacts with p130Cas as both proteins co-immunoprecipitate and co-localize in Oli-neu cells and primary oligodendrocytes.