Altered expression of pp60c-src induced by peripheral nerve injury

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Abstract
The normal src protein (pp60c‐src) is localized principally in the nerve growth cone of developing neurons and declines to low levels with synaptic maturation. To determine whether pp60c‐src is reexpressed in regenerating axons, its expression was studied by immunoblotting and immunocytochemical analyses in adult chicken sciatic nerve following nerve crush injury. pp60c‐src expression was found to increase during nerve repair with a temporal and spatial pattern consistent with a localization in regenerating axons. At the crush site, pp60c‐src increased to maximal levels 7 days postinjury, increasing fivefold relative to 0 day nerve. In the nerve segment distal to the injury, the maximal increase in pp60c‐src was sevenfold and occurred between 11 and 21 days postinjury. Immunoperoxidase staining revealed pp60c‐src in regenerating axons and certain nonneuronal cells at the site of nerve repair. pp60c‐src was induced in both motor and sensory neurons, as shown by increased pp60c‐src immunoreactivity in their cell bodies located in the spinal cord and dorsal root ganglion. Phosphotyrosine‐modified proteins that were potential targets of pp60c‐src increased following nerve crush, and were localized to outgrowing neurites as well as to nonneuronal cells. These results suggest that pp60c‐src is a common component of cellular mechanisms regulating growth cone migration in both regenerating and developing axons.