Neural tubes of E8-5 day mouse embryos were dissected and cultured in serum substitute-supplemented medium to allow the emigration of neural crest cells. After 48 h of culture the neural tubes were removed. The neural crest cells were then cultured for 12 h in serum-free medium, and their culture supernatant was studied by electrophoresis and zymography. The cultured cells were shown to secrete both urokinase-type and tissue-type plasminogen activators. When the truncal neural tube was divided in four equal segments, the secretion pattern of the two types of plasminogen activators was similar for the cells from the three most anterior segments; cells having migrated from the most caudal one, i.e. consisting of the neural plate, secreted a higher level of urokinase-type plasminogen activator. The secretion in vitro of plasminogen activators by neural crest cells is in accord with the postulated importance of these proteases in cellular migration.

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