TRANSFORMING GROWTH-FACTOR BETA(1) EXPRESSION IN THE ENDOMETRIUM OF THE MARE DURING PLACENTATION

In situ hybridization, Northern blotting, and immunohistochemical tech niques were used to study the expression of transforming growth factor beta 1 (TGF beta(1)) in the endometrium of the mare during the first 150 days of pregnancy (term = 330-340 days). In situ hybridization usi ng an oligonucleotide (45mer) probe, based on a homologous region with in all known mammalian TGF beta(1) DNA sequences, demonstrated TGF bet a(1) mRNA accumulation in the glandular and lumenal epithelial cells o f the endometrium from day 33 onwards which corresponds to the time of implantation (day 33-45). Expression in the endometrium remained at a high level to the end of the sampling period (day 150). There was als o marked expression of TGF beta(1) in the mononuclear cells accumulate d around the periphery of the specialized trophoblast cells of the end ometrial cup within the endometrium and in the mononuclear cells accum ulated in the endometrial stroma of mares carrying failing donkey-in-h orse pregnancies created by embryo transfer. The sense (control) oligo nucleotide probe exhibited no hybridization to any tissue at any stage . Northern blot analysis demonstrated that the oligonucleotide probe a nd a porcine TGF beta(1) cDNA clone hybridized to a single 2.5 kb tran script in horse endometrial and lymphocyte RNA, thus validating the ol igonucleotide probe for detection of horse TGF beta(1) mRNA. Furthermo re, both probes demonstrated an increased signal in the pregnant endom etrium from day 33 onwards, thereby confirming the in situ hybridizati on results. Immunostaining with a specific anti-bovine TGF beta(1) ser um also showed increasing TGF beta(1) accumulation in endometrial epit helia during pregnancy, and localization of the protein in endometrial stroma and in the trophoblast layer of the placenta after day 60 of p regnancy. These results show that TGF beta(1) expression increases in the maternal endometrium of the mare at the time of implantation and t hat it may play a role in regulating endometrial and/or trophoblast gr owth and differentiation during placentation in this species. It may a lso influence fetal development (via placental transfer) at a later st age of gestation. (C) 1995 Wiley-Liss, Inc.