By contrast, dlk-1 overexpression can restore regeneration in aged animals ( Hammarlund et al., 2009). Next, we determined that the DLK-1 pathway does not regulate regeneration via Notch. We found that absence of Notch signaling—which increases regeneration—is unable to bypass the requirement for dlk-1. We examined regeneration in dlk-1; sup-17 double mutants, which lack both Notch signaling
and dlk-1 signaling. These animals regenerated as poorly as dlk-1 single mutants, suggesting that inhibition of Notch is not the major effect of the dlk-1 pathway ( Figure 6E). Together, these experiments suggest that Notch and dlk-1 signaling may act independently to regulate regeneration. Alternatively, Notch may act at the time of injury to acutely limit activity of the dlk-1 pathway. Our
results identify a postdevelopmental role for Notch signaling: inhibition of Ponatinib price axon regeneration. Notch signaling inhibits Ipatasertib purchase regeneration via a canonical activation pathway, involving Notch/lin-12, the metalloprotease ADAM10/sup-17, and the gamma-secretase complex. These factors release the NICD of Notch/lin-12 into the cytoplasm. The NICD localizes to the nucleus and is sufficient to inhibit regeneration, suggesting that a nuclear function of the NICD mediates Notch inhibition of regeneration. In the GABA neurons studied in this work, not all Notch pathway components affect regeneration. Specifically, the other C. elegans Notch, Notch/glp-1, and the other metalloprotease that mediates Notch signaling, ADAM17/adm-4, do not affect regeneration of the GABA neurons. However, both the NICD of Notch/glp-1 and ADAM17/adm-4 inhibit regeneration when overexpressed in GABA neurons. These data suggest that the different effects of the endogenous Notch components on axon regeneration are not due to different target specificities or intracellular activation mechanisms. Rather, lack of expression of Notch/glp-1 and ADAM17/adm-4 in the GABA neurons could account for the lack of endogenous inhibitory activity of these genes. Consistent with Cediranib (AZD2171) this idea, Notch/glp-1
is expressed in some postmitotic neurons, but not in GABA neurons ( Ouellet et al., 2008), and ADAM/adm-4 is not expressed in adult neurons ( Hunt-Newbury et al., 2007). Thus, Notch signaling can function generally to restrict regeneration, at least in GABA neurons. Notch signaling usually acts by regulating gene transcription via a CSL-family transcription factor. Although we were unable to demonstrate a role in inhibition of regeneration for the single C. elegans CSL factor, CSL/lag-1, two lines of evidence suggest that regulation of gene transcription may account for Notch’s ability to inhibit regeneration. First, the Abl signaling pathway, which mediates nontranscriptional function of the NICD ( Giniger, 1998 and Le Gall et al., 2008), does not regulate axon regeneration ( Figure 3I).