EXPRESSION OF PROTEINASES AND PROTEINASE-INHIBITORS DURING EMBRYO-UTERINE CONTACT IN THE PIG

Implantation in pigs is noninvasive and characterized by interdigitati on of embryonic and endometrial epithelial cell processes. However whe n pig embryos are transferred to ectopic sites, trophoblast becomes in vasive, The objective of this study was to evaluate expression of prot einases and proteinase inhibitors in pig embryos and uteri at the time of endometrial attachment. RNA was extracted from Day 15.75 pig embry os and uteri and reverse transcribed, and cDNA was amplified by polyme rase chain reactions using primers specific for urokinase-type plasmin ogen activator (UPA), matrix metalloproteinases-2 and -9 (MMP-2 and -9 ), and tissue inhibitors of MMP-1, -2, and -3 (TIMP-1, 2, and -3). Loc alization of transcripts for the genes of interest in embryos and uter i was performed using in situ hybridization with antisense riboprobes. Day 15.75 pig embryos and uteri expressed transcripts for UPA, MMP-2 and -9, and TIMP-1, -2, and -3. in situ hybridization revealed weak ex pression of UPA in the trophectoderm and moderate expression in the ad jacent extraembryonic endoderm. TIMP-1 transcripts were abundant in ex traembryonic endoderm and scattered throughout the trophectoderm. TIMP -2 appeared to be expressed in ail cells of the embryo. TIMP-3 express ion wa observed in the trophectoderm and, to a lesser extent, in the e xtraembryonic endoderm. Specific localization of MMP-2 and -9 transcri pts above background was not observed by in situ hybridization in eith er embryos or uterus. Uterine expression of UPA and TIMP-1, -2, and -3 was localized to the endometrial stroma. Transcripts of these genes w ere not observed in either the luminal or glandular endometrial epithe lium. These results suggest that pig embryos and uteri express a wide array of proteinases and proteinase inhibitors during the period of ut erine association. The abundant expression of TIMP in pig embryos may partially explain the absence of invasive implantation in this species in contrast to implantation typified by rodents and primates. (C) 199 7 Wiley-Liss, Inc.