Caenorhabditis elegans F-Box Protein Promotes Axon Regeneration by Inducing Degradation of the Mad Transcription Factor

J Neurosci. 2021 Mar 17;41(11):2373-2381. doi: 10.1523/JNEUROSCI.1024-20.2021. Epub 2021 Jan 29.


In Caenorhabditis elegans, axon regeneration is activated by a signaling cascade through the receptor tyrosine kinase (RTK) SVH-2. Axonal injury induces svh-2 gene expression by degradation of the Mad-like transcription factor MDL-1. In this study, we identify the svh-24/sdz-33 gene encoding a protein containing F-box and F-box-associated domains as a regulator of axon regeneration in motor neurons. We find that sdz-33 is required for axon injury-induced svh-2 expression. SDZ-33 targets MDL-1 for poly-ubiquitylation and degradation. Furthermore, we demonstrate that SDZ-33 promotes axotomy-induced nuclear degradation of MDL-1, resulting in the activation of svh-2 expression in animals. These results suggest that the F-box protein is required for RTK signaling in the control of axon regeneration.SIGNIFICANCE STATEMENT In Caenorhabditis elegans, axon regeneration is positively regulated by the growth factor SVH-1 and its receptor tyrosine kinase SVH-2. Expression of the svh-2 gene is induced by axonal injury via the Ets-like transcription factor ETS-4, whose transcriptional activity is inhibited by the Mad-like transcription factor MDL-1. Axon injury leads to the degradation of MDL-1, and this is linked to the activation of ETS-4 transcriptional activity. In this study, we identify the sdz-33 gene encoding a protein containing an F-box domain as a regulator of axon regeneration. We demonstrate that MDL-1 is poly-ubiquitylated and degraded through the SDZ-33-mediated 26S proteasome pathway. These results reveal that an F-box protein promotes axon regeneration by degrading the Mad transcription factor.

Keywords: C. elegans; Mad/Max; axon regeneration; ubiquitin.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acids / metabolism
  • Animals
  • Animals, Genetically Modified
  • Axons / physiology
  • Axotomy
  • Caenorhabditis elegans
  • Caenorhabditis elegans Proteins / genetics
  • Caenorhabditis elegans Proteins / physiology*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / physiology*
  • F-Box Proteins / genetics
  • F-Box Proteins / physiology*
  • Motor Neurons / physiology
  • Nerve Regeneration / genetics
  • Nerve Regeneration / physiology*
  • Plasmids
  • Receptor Protein-Tyrosine Kinases / genetics
  • Receptor Protein-Tyrosine Kinases / metabolism
  • Receptor Protein-Tyrosine Kinases / physiology
  • Ubiquitin


  • Amino Acids
  • Caenorhabditis elegans Proteins
  • DNA-Binding Proteins
  • F-Box Proteins
  • Ubiquitin
  • mdl-1 protein, C elegans
  • Receptor Protein-Tyrosine Kinases
  • SVH-2 protein, C elegans