N‐WASP regulates extension of filopodia and processes by oligodendrocyte progenitors, oligodendrocytes, and Schwann cells—implications for axon ensheathment at myelination

Abstract

The molecular mechanisms used by oligodendrocyte precursor cells (OPCs), oligodendrocytes (OLs), and Schwann cells (SCs) to advance processes for motility in the developing nervous system and to ensheath axons at myelination are currently not well defined. Here we demonstrate that OPCs, OLs, and SCs express the major proteins involved in actin polymerization-driven protrusion; these key proteins including F-actin, the Arp2/3 complex, neural-Wiskott Aldrich Syndrome protein (N-WASP) and WAVE proteins, and the RhoGTPases Rac and Cdc42 are present at the leading edges of processes being extended by OPCs, OLs, and SCs. We reveal by real-time PCR that OLs and SCs have different dominant WAVE isoforms. Inhibition of the WASP/WAVE protein, N-WASP, with wiskostatin that prevents activation of the Arp2/3 complex, blocks process extension by OPCs and SCs. Inhibition of N-WASP also causes OPC and SC process retraction, which is preceded by retraction of filopodia. This implicates filopodia in OPC and SC process stability and also of N-WASP in OPC and SC process dynamics. We also demonstrate that p34 (a component of the Arp2/3 complex), WASP/WAVE proteins, actin, alpha-tubulin, Rac, Cdc42, vinculin, and focal adhesion kinase are detected in water-shocked myelin purified from brain. Inhibition of N-WASP with wiskostatin decreases the number of axons undergoing initial ensheathment in intact optic nerve samples and reduces the Po content of dorsal root ganglia:SC co-cultures. Our findings indicate that OPCs, OLs, and SCs extend processes using actin polymerization-driven protrusion dependent on N-WASP. We hypothesize that inner mesaxons of OLs and SCs use the same mechanism to ensheath axons at myelination.

Elevated Phosphatidylinositol 3,4,5-Trisphosphate in Glia Triggers Cell-Autonomous Membrane Wrapping and Myelination

“…The activity of GEFs (guanine nucleotide exchange factors), Rho GTPases (Rac1 and CDC42), and Rac effector proteins [such as WAVE (WiskottAldrich syndrome protein family verprolin-homologous protein) and WASP (Wiskott-Aldrich syndrome protein) proteins] is regulated by PIP3 and leads to the localized polymerization of F-actin (Charest and Firtel, 2007). These proteins have been independently implicated in oligodendrocyte and Schwann cell development, process extension, axonal sorting, and myelination (Kim et al, 2006;Thurnherr et al, 2006;Bacon et al, 2007;Benninger et al, 2007;Nodari et al, 2007;Stendel et al, 2007). PTEN itself harbors a C-terminal PDZ (postsynaptic density-95/ Discs large/zona occludens-1) binding motif and interacts with Par3 and Dlg1 (Adey et al, 2000;Feng et al, 2008).…”

Herpes simplex virus type 1 induces filopodia in differentiated P19 neural cells to facilitate viral spread

“…However, glial responses to HSV-1 infection may affect normal axonal myelination in vivo [2], and hence negatively influence action potential propagation in chronically infected neural systems. This could help explain previous reports of demyelination of CNS axons after herpes infection [31].…”

“…Given that dendritic filopodia play an early role in synaptogenesis [34], [13], [24] and [8] the observation of new filopodia formation and cytoskeletal rearrangement in response to acute HSV-1 infection could be linked with the cognitive deficits found in herpes-mediated encephalitis patients [16] and [27]. Glial cytoskeletal reorganization may similarly have some bearing on normal CNS function [2]. While it remains unclear whether these preliminary in vitro results can be extended to a physiological paradigm, our findings raise the intriguing possibility that acute HSV-1 infection may prompt some degree of synaptic dysfunction in the brain.…”

Netrin 1 and Dcc regulate oligodendrocyte process branching and membrane extension via Fyn and RhoA

“…Interestingly, a number of the same intracellular signaling proteins have been implicated in netrin-1-mediated axon guidance and the development of oligodendrocyte processes required for myelination (Fox et al, 2006;Jarjour and Kennedy, 2004). In both cases, the reorganization of the actin cytoskeleton requires activation of the Src family kinase (SFK) Fyn (Meriane et al, 2004;Osterhout et al, 1999;Umemori et al, 1994) and involves Wiscott-Aldrich syndrome protein (N-WASP; Wasl -Mouse Genome Informatics) and Rho GTPases (Bacon et al, 2007;Liang et al, 2004;Shekarabi et al, 2005).…”