EXPRESSION OF A PLASMIN TRYPSIN KUNITZ INHIBITOR BY PIG TROPHOBLAST/

Under the influence of progesterone, the porcine uterus synthesizes pl asmin/trypsin inhibitor (PTI), a low molecular weight protein (M(r) si milar to 14,000) belonging to the Kunitz family of proteinase inhibito rs. Here it is demonstrated that mRNA for the same protein is produced by the developing trophoblast during early pregnancy and by the place nta throughout gestation. The transcript for PTI was represented in ap proximately 0.1% of total phage plaques of a day 13-17 porcine concept us cDNA library. It shared 99% nucleotide sequence identity with the c DNA isolated from the uterine library and encoded a 112-amino-acid pro tein identical to the uterine-produced PTI, which has a well-defined K unitz domain comprised of 64 residues at its amino terminus. Northern analysis and in situ hybridization studies confirmed that expression o f PTI by the conceptus begins as early as day 10 of pregnancy and is c ontinued in placental tissues until at least day 90 of gestation. Expr ession was trophoblast specific at day 20 of gestation, as in situ hyb ridization detected no mRNA in the embryo. The pattern of PTI expressi on during pregnancy is consistent with a role either in controlling tr ophoblast invasiveness or in inhibiting proteinases with trypsin-like specificity released by immune or inflammatory cells. (C) 1997 Wiley-L iss, Inc.