Extracellular proteolysis: developmentally regulated activity during chick spinal cord histogenesis.

The present study was performed to identify at which stages during spinal cord histogenesis the extracellular proteolysis (i.e. the plasmin-generating system) is expressed by the developing tissue. We report that the embryonic chick spinal cord in the course of its histogenesis produces the protease, plasminogen activator. Specific activity of plasminogen activator in the developing embryo was monitored daily, in whole cords (from day 4 until hatching) and in the ventral and dorsal halves of the cord (6-17 days) and was biochemically determined by the fibrinolytic assay. The enzyme-specific activity of the developing cord was found to be very low at early embryonic stages when neuroblasts proliferate and it is markedly enhanced (14-fold at its maximal level) at later stages when the neurons are postmitotic and only the glial cells proliferate. The pattern of plasminogen activator specific activities does not remain at a constant level: it appears to be developmentally regulated, since it is decreased and enhanced during 3 temporal stages of the spinal cord histogenesis. These coincide with the stages when a transient increase in cell proliferation, presumably of glia, was monitored as determined daily by the spinal cord DNA content (microgram DNA/mg protein). Furthermore, on days 7-9 of embryonic age, the two halves of the cord differ in their plasminogen activator specific activities; activity levels of the ventral halves were found to be higher than their dorsal counterparts with significant difference on day 7. These correspond with the well-established differentiation gradient in the ventral-to-dorsal axis of the cord.(ABSTRACT TRUNCATED AT 250 WORDS)