Axon regeneration is an evolutionarily conserved process from nematodes to humans. Recently, we have identified a growth factor SVH-1 and its receptor tyrosine kinase SVH-2 as positive regulators of axon regeneration in Caenorhabditis elegans. Axon cutting by laser microsurgery induces the transcription of the
svh-2 gene specifically in severed neurons. However, the mechanism by which how the
svh-2 gene is induced in response to axon cutting is not well understood. In this study, we identified
ets-4, an Ets transcription factor, as a regulator involved in the transcriptional induction of the
svh-2 gene. In
ets-4 null mutants,
svh-2 induction by axon cutting did not occur, and frequency of axon regeneration was greatly reduced. This reduction can be suppressed by forced expression of the
svh-2 gene in severed neurons by the constitutive promoter. As the
svh-2 promoter region contains the consensus sequences of the Ets-binding site, we executed mutational analysis of these sites and found that one of them is required for the transcriptional induction of the
svh-2 gene. Previous studies revealed that cyclic AMP (cAMP) and Protein kinase A (PKA) promotes axon regeneration in many organisms, including C. elegans. As ETS-4 protein contains a PKA phosphorylation consensus sequence (Arg-Arg-Xxx-Ser) at Ser-73, we performed in vitro kinase assays and found that PKA can phosphorylate ETS-4 on Ser-73. Further functional analysis revealed that the phosphorylation of this residue is important for the function of ETS-4 in the activation of the regeneration pathway. Furthermore, we found that the cAMP synthesis gene
acy-1 is also required for the transcriptional induction of
svh-2 in severed neurons. These results suggest that the cAMP-PKA signal induces the
svh-2 transcription via phosphorylation of ETS-4 in axon regeneration. .