Post‐translational regulation of Crmp in developing and regenerating chick spinal cord

It is becoming apparent that regulation at the protein level plays crucial roles in developmental and pathological processes. Therefore, we performed a proteomics screen to identify proteins that are differently expressed or modified at stages of development permissive (E11) and nonpermissive for regeneration (E15) of the chick spinal cord. Proteins regulated either developmentally or in response to spinal-cord injury included collapsin-response-mediator proteins (Crmps), known to modulate microtubule dynamic and axonal growth. No significant changes in Crmp transcripts following injury were observed, indicating regulation mainly at the protein level. Analysis of Crmp-2 protein and its phosphorylated forms, pS522 and pT514, showed that Crmp-2 is developmentally regulated and also expressed in neural progenitors in vivo and in neurospheres. Its cellular localization changed both with development and following spinal-cord injury. In addition, although overall levels of Crmp-2 expression were not affected by injury, abundance of certain phosphorylated forms was altered. pT514 Crmp-2 appeared to be associated with dividing neural progenitors and was greatly reduced at nonpermissive stages for regeneration, whereas it did not seem affected by injury. In contrast, phosphorylation of Crmp-2 at S522 was upregulated early after injury in regenerating spinal cords and the ratio between phosphorylated to total Crmp-2 increased, as indicated by 2D Western blots. Altogether, this study shows highly dynamic regulation of Crmp-2 forms during development and identifies post-translational changes in Crmp-2 as putative contributors to the maintenance of spinal-cord regenerative ability, possibly via a transient stabilization of the neuronal cytoskeleton.