A plasminogen activator is induced during goldfish optic nerve regeneration

The use of purified piscine plasminogen in a chromogenic solution assay enabled us to detect plasminogen activator (PA) activity in crude homogenates of goldfish optic nerve following nerve injury. In contrast, no activity was detected in the homogenates of uninjured nerve. Under conditions allowing regeneration of the optic axons (optic nerve crush), PA activity peaked 8 days after crush, and decreased to undetectable levels by 60 days. Under conditions allowing only degeneration of the axons (enucleation), the activity peaked at 8 days but decreased more rapidly. Casein zymography of samples after fractionation in SDS-PAGE showed that PA activity migrated as a doublet at Mr = 60-65 kd. Using this assay, activity was also observed in uninjured control nerves. This plasminogen-dependent activity migrated as three bands of higher molecular weight (Mr = 75, 95 and 120 kd) and was undetectable in solution assays of unfractionated extracts, suggesting complex formation with an inhibitor(s). Fibrin overlay assay of retinal explants and isolated primary cells in culture suggest that the goldfish PA is associated with the glial cells of the goldfish visual pathway.