Plasminogen activator in the bursa of Fabricius: correlations with morphogenetic remodeling and cell migrations.

The association of controlled extracellular proteolysis, mediated by plasminogen activator, with embryonic tissue remodeling and cell migration was studied in the developing bursa of Fabriculus of quail and chick embryos. We found: that the specific activity of plasminogen activator in the bursa changes as a function of developmental age; that these changes are correlated temporally with the migration of hemopoietic cells into the bursal rudiment and with the period of extensive remodeling in the bursal epithelium; that the enzyme is distributed asymmetrically in the epithelial and mesenchymal compartments of the bursa. Chick and quail plasminogen activators can be distinguished by differences in their rates of electrophoretic migration. When interspecific grafts between quail and chick embryos were analyzed in this way, we observed that hemopoietic precursor cells produce plasminogen activator during their colonization of the bursa.