DEVELOPMENTAL PATTERN OF PLASMINOGEN-ACTIVATOR ACTIVITY IN CHICK OPTIC LOBE

Plasminogen activators are serine proteases which play a key role in m orphogenesis and tissue remodelling. Two different molecular types, ti ssue-type and urokinase-type, were identified and they were postulated to play a role in neural development. The developing chick optic lobe plays a central role in processing visual information. In previous st udies we demonstrated the occurrence of high levels of plasminogen act ivator activity in this model. The aim of the present paper is to stud y the temporal pattern of expression of this activity and characterize the type of plasminogen activator expressed in the developing optic l obe. Using soluble fractions derived by ultracentrifugation from Trito n X-100-treated membrane fractions we measured the protease activity w ith a radial fibrinolytic assay. Employing different inhibitors of fib rinolytic activity and a zymographic assay, we showed that the develop ing optic lobe expresses only one type of plasminogen activator which corresponds to an urokinase-type of 70 kDa. Our results indicate that peaks of protease activity temporally correlate with massive neuronal migration, neurite outgrowth and synapse formation and maturation. Thi s suggests that a plasminogen activator could play a role in these dev elopmental events. This consistent pattern of variability strongly sug gests that it is developmentally regulated and, if so, it could be a r eliable parameter to study neural plastic changes induced by modificat ions in the environmental stimulation. (C) 1997 ISDN.