The production of distinct forms of plasminogen activator by mouse embryonic cells

We have examined cultured parietal endoderm, visceral endoderm, and extraembryonic mesoderm cells from the mouse embryo for production of the protease plasminogen activator. All of these cell types synthesize and secrete the enzyme, but the molecular characteristics of the plasminogen activators differ as defined by the apparent molecular weight in sodium dodecyl sulfate-polyacrylamide gels, the antigenic properties as defined by two antisera to distinct plasminogen activators, and the interaction with an inhibitor present in fetal bovine serum. The parietal endoderm plasminogen activator has a predominant molecular weight of 79,000, is immunoprecipitated and inhibited by an antiserum raised against a human melanoma plasminogen activator, but not by an antiserum against mouse urokinase, and is only partially inhibited by the serum inhibitor. The visceral endoderm and extraembryonic mesoderm plasminogen activators, which are identical by all criteria, have molecular weights of 48,000, are inactivated only by the anti-urokinase antibodies, and are inhibited by an inhibitor in fetal bovine serum. These results establish the presence of at least two different forms of plasminogen activator in the early mouse embryo. The distinctive nature of the enzyme produced by parietal endoderm can be used as a diagnostic marker for this cell type at this stage of development. When F9 teratocarcinoma stem cells are induced to differentiate by retinoic acid and dibutyryl cAMP, they secrete a plasminogen activator of the parietal endoderm type.