The distribution of mRNAs and antigens of tissue type (t) and urokinase type (u) plasminogen activators
(PA) plus their corresponding inhibitors, type-1 (PAI-1) and type-2 (PAI-2) were studied in human and
rhesus monkey placentae by in situ hybridisation and immunocytochemistry. Specific monkey cRNA and
antibodies against human tPA, uPA, PAI-1 and PAI-2 were used as probes. The following results were
obtained. (1) All the molecules tPA, uPA, PAI-1 and PAI-2 and their mRNAs were identified in the
majority of the extravillous cytotrophoblast cells of the decidual layer between Rohr's and Nitabuch's striae
and in cytotrophoblast cells of the chorionic plate, basal plate, intercotyledonary septae and cytotrophoblast
cells of the chorionic villous tree. (2) Expression of uPA and PAI-2 was noted in villous trophoblast whereas
tPA and PAI-1 were mainly concentrated where detachment from maternal tissue occurs. (3) No expression
of tPA, uPA, PAI-1 and PAI-2 was observed in the basal plate endometrial stromal cells, chorionic plate
connective tissue cells, septal endometrial stromal cells or villous core mesenchyme. (4) The distribution of
probes observed following in situ hybridisation is generally consistent with the immunofluorescence pattern
of the corresponding antigens and no significant interspecies differences were noted. It is possible that both
decidual and extravillous trophoblast cells of placentae of human and rhesus monkey are capable of
producing tPA, uPA, PAI-1 and PAI-2 to differing extents. Coordinated expression of these genes in the
tissue may play an essential role in the maintenance of normal placentation and parturition. The differences
in distribution we observed are consistent with the suggestion that coordinated expression of tPA and its
inhibitor PAI-1 may play a key role in fibrinolytic activity in the early stages of placentation and separation
of placenta from maternal tissue at term. On the other hand, uPA with its inhibitor PAI-2 appears mainly
to play a role in degradation of trophoblast cell-associated extracellular matrix, and thus may be of greatest
importance during early stages of placentation.