The extracellular matrix proteoglycan perlecan facilitates transmembrane semaphorin-mediated repulsive guidance

Abstract

The Drosophila transmembrane semaphorin-1a (Sema-1a) is a repulsive guidance cue that uses the Plexin A (PlexA) receptor during neural development. Sema-1a is required in axons to facilitate motor axon defasciculation at guidance choice points. We found that mutations in the trol gene strongly suppress Sema-1a-mediated repulsive axon guidance. trol encodes the phylogenetically conserved secreted heparan sulfate proteoglycan (HSPG) perlecan, a component of the extracellular matrix. Motor axon guidance defects in perlecan mutants resemble those observed in Sema-1a-and PlexA-null mutant embryos, and perlecan mutants genetically interact with PlexA and Sema-1a. Perlecan protein is found in both the CNS and the periphery, with higher expression levels in close proximity to motor axon trajectories and pathway choice points. Restoring perlecan to mutant motor neurons rescues perlecan axon guidance defects. Perlecan augments the reduction in phospho-focal adhesion kinase (phospho-FAK) levels that result from treating insect cells in vitro with Sema-1a, and genetic interactions among integrin, Sema-1a, and FAK in vivo support an antagonistic relationship between Sema-1a and integrin signaling. Therefore, perlecan is required for Sema-1a-PlexA-mediated repulsive guidance, revealing roles for extracellular matrix proteoglycans in modulating transmembrane guidance cue signaling during neural development.

Function of theDrosophilareceptor guanylyl cyclase Gyc76C in PlexA-mediated motor axon guidance

“…Sema-1a is enriched in Drosophila embryonic neurons and mediates axonal repulsion, ensuring proper axon pathfinding (Winberg et al, 1998b;Yu et al, 1998;Ayoob et al, 2004;Cho et al, 2012;Jeong et al, 2012). During neural development, motor axons exit the CNS in two large bundles that include multiple motor axons which then segregate into smaller motor nerves: the intersegmental nerves (ISNs: ISNb and ISNd) and the segmental nerves (SNs: SNa and SNc) (Landgraf et al, 1997).…”

Epidermis-Derived Semaphorin Promotes Dendrite Self-Avoidance by Regulating Dendrite-Substrate Adhesion in Drosophila Sensory Neurons

“…In mammals, activation of integrins signals through focal-adhesion kinase (FAK) family proteins to promote outgrowth of neurites (Ivankovic-Dikic et al, 2000), and semaphorin treatment has been shown to exert changes on Fak phosphorylation (Cho et al, 2012). Therefore, we tested if Fak is also required for dendrite-ECM adhesion in class IV da neurons.…”

“…Previous studies show that crosstalk between semaphorin and integrin signaling leads to inhibition of integrin-mediated adhesion in both invertebrates and vertebrates (Tamagnone and Comoglio, 2004; Kruger et al, 2005; Cho et al, 2012). For example, semaphorin-mediated signaling decreases integrin-mediated attachment during vascular morphogenesis (Serini et al, 2003).…”

Transmembrane semaphorins: Multimodal signaling cues in development and cancer

“…This forward signaling cascade is modulated by perlecan, an extracellular matrix component, which enhances semaphorin-induced downregulation of integrin adhesive function and FAK dephosphorylation, leading to motor axon defasciculation. 15 Notably, Sema1a can also mediate motor axon defasciculation through reverse signaling mechanisms, whereby its cytoplasmic domain can interact with two major antagonistic regulators of the GTPase Pebble and the inhibitor RhoGAP p190. The first activates Rho1 and promotes axon-axon repulsion and defasciculation, while p190-RhoGAP antagonizes this mechanism allowing axonal attraction; 16,17 the extracellular Sema1a-binding molecule triggering this cascade is still unclear.…”