Axon regeneration

is influenced in many ways by the extracellular environment. We tested approximately 60 genes encoding extracellular matrix components, putative cell adhesion proteins, and cell surface receptors (Figure 3A). Several such genes were required for regrowth (Table 1), including the cell surface proteoglycan SDN-1/Syndecan (Rhiner et al., 2005), the L1CAM ortholog SAX-7/LAD-1 (Chen et al., 2001), the novel GPIlinked IgCAM RIG-3, and the IgCAM RIG-4/Sidekick (Schwarz et al., 2009). In vertebrate axons L1 is upregulated after injury and required for regrowth (Becker et al., 2004); however, syndecans or sidekick family members have not previously been implicated in axon regeneration. Conversely, loss of function in several putative basement membrane components, such as spon-1/F-spondin ( Woo et al., 2008) or pxn-2/Peroxidasin ( Gotenstein et al., 2010) resulted in enhanced regrowth INCB28060 ( Table 2). In vertebrates the “glial scar” is an ECM barrier to CNS regeneration ( Busch and Silver, 2007); although C. elegans does not encode orthologs of glial scar components such as chondroitin sulfate proteoglycans, these observations raise the possibility that the basement membrane

forms an analogous barrier to PLM regrowth. Wnt signals selleck compound regulate the polarity of PLM neurite outgrowth in development (Hilliard and Bargmann, 2006). We find PLM regrowth involves distinct Wnt signals. For example the Wnt CWN-2 is not required for PLM development yet is required for regrowth (Table 1). CWN-2 is expressed anterior to PLM, suggesting it could

be permissive or attractive in PLM regrowth, similar to its roles in other neurons (Kennerdell et al., 2009 and Song et al., 2010). Among tested axon guidance pathways, Slit-Robo signaling had an inhibitory effect on regeneration. Both slt-1/Slit and sax-3/Robo null mutants displayed increased PLM regrowth, and slt-1 sax-3 double mutants showed no further enhancement in axon regeneration than either single mutant ( Figures 3B and 3C). Further, overexpression of SAX-3 in touch neurons inhibited many PLM regrowth, indicating SAX-3/Robo can act cell autonomously to restrain regrowth ( Figure 3B). Constitutive expression of SLT-1 from body wall muscles also reduced PLM regrowth in a SAX-3-dependent manner ( Figure 3B). In development, SAX-3 activity has a minor role in promoting PLM outgrowth ( Li et al., 2008). To address whether SAX-3 acts at the time of regrowth or earlier we performed temperature shift experiments on sax-3(ky200ts) ( Zallen et al., 1998) and found that animals shifted to the restrictive temperature immediately postaxotomy exhibited increased regrowth equivalent to sax-3 null mutants ( Figure 3D), indicating that SAX-3 acts at the time of regrowth. Last, we addressed when in regrowth SLT-1 and SAX-3 signals acted.