Dystroglycan Organizes Axon Guidance Cue Localization and Axonal Pathfinding

Abstract

Precise patterning of axon guidance cue distribution is critical for nervous system development. Using a murine forward genetic screen for novel determinants of axon guidance, we identified B3gnt1 and ISPD as required for the glycosylation of dystroglycan in vivo. Analysis of B3gnt1, ISPD and dystroglycan mutant mice revealed a critical role for glycosylated dystroglycan in the development of several longitudinal axon tracts. Remarkably, the axonal guidance defects observed in B3gnt1, ISPD and dystroglycan mutants resemble those found in mice lacking the axon guidance cue Slit and its receptor Robo. This similarity is explained by our observations that dystroglycan binds directly to Slit and is required for proper Slit localization within the basement membrane and floor plate in vivo. These findings establish a novel role for glycosylated dystroglycan as a key determinant of axon guidance cue distribution and function in the mammalian nervous system.

Slit-Robo signaling

“…Slits can also homodimerize; the LRR4 domain is required for this dimerization (Seiradake et al, 2009). Importantly, Slits show additional heterophilic binding to other ECM molecules, including Neurexins, Type IV Collagens (Xiao et al, 2011), Netrin 1 , dystroglycan (Wright et al, 2012), Glypican (Liang et al, 1999) and Syndecan (Johnson et al, 2004;Steigemann et al, 2004).…”

“…Slit-C was recently shown to bind plexin A1 and to induce growth cone collapse of mouse spinal cord commissural axons (DelloyeBourgeois et al, 2014). In addition, Slit-C binds to the basement membrane scaffolding protein dystroglycan (Wright et al, 2012).…”

“…Indeed, a candidate Slit receptor, Eva1C, first identified in C. elegans (Fujisawa et al, 2007), is expressed in Slit-responsive axons in the mouse (James et al, 2013). As mentioned above, Slit fragments can also bind to the semaphorin receptor plexin A1 to to induce commissural axon chemorepulsion (Delloye-Bourgeois et al, 2014) and to dystroglycan, which is also expressed in the floor plate (Wright et al, 2012) suggesting that dystroglycan captures Slit-C at its sites of action; accordingly, dystroglycan mutant mice phenocopy the spinal cord midline defects seen in Robo1;2 double mutants. As in Drosophila (Rajagopalan et al, 2000;Simpson et al, 2000), SlitRobo repulsion might also influence the lateral positioning of axons extending parallel to the CNS midline axis (Spitzweck et al, 2010).…”

Dystroglycan mediates homeostatic synaptic plasticity at GABAergic synapses

“…α-DG docks with transmembrane β-DG to form the functional core of the dystrophinassociated glycoprotein complex (DGC) that links adhesive proteins in the extracellular matrix to dystrophin (5). α-DG is heavily glycosylated and interacts via its carbohydrate side chains with laminin and laminin G-like domains in a variety of proteins including agrin, perlecan, slit, neurexin, and pikachurin (6)(7)(8)(9)(10). Key carbohydrate residues are added onto α-DG by several glycosyltransferases, most notably like-acetylglucosaminyltransferase (LARGE) (11).…”

Endogenous Glucuronyltransferase Activity of LARGE or LARGE2 Required for Functional Modification of α-Dystroglycan in Cells and Tissues

“…␤3GnT1, which is involved in the synthesis of poly-N-acetyllactosamine (18) and whose sequence is closely related to the second domain of LARGE (19), has been shown to contribute to the synthesis of the laminin-binding glycan of ␣-DG through formation of a complex with LARGE (20). Moreover, a study using a forward genetic screen demonstrated that ␤3GnT1 is required for functional glycosylation of ␣-DG in vivo; mice expressing a mutant form of this protein exhibited axonal-guidance defects like those observed in ISPD or an epiblast-specific DG mutant mouse (21). Recently, SGK196 was found to be a protein O-mannose kinase (designated as POMK) that generates [GalNAc-␤3-GlcNAc-␤4-(phosphate-6-)Man], a modification required for the functional glycosylation of ␣-DG (22).…”