EXPRESSION OF EPIDERMAL GROWTH-FACTOR AND ITS RECEPTOR IN EQUINE PLACENTAL TISSUES

Northern blot and in situ hybridization techniques have demonstrated a marked increase in mRNA encoding epidermal growth factor (EGF) in the endometrium of mares, coincident with the start of interdigitation be tween the allantochorion and endometrium during placentation. In the p resent study, the unusually high EGF expression in the epithelium of t he endometrial glands was shown to be maintained until at least day 25 0 of gestation (term = 320-340 days) in mares carrying normal horse co nceptuses. However, in mares carrying failing donkey-in-horse pregnanc ies created by embryo transfer, EGF expression was severely retarded i n those areas of the endometrium that were heavily infiltrated with ly mphocytes and which showed a failure of placental development. Specifi c receptors for EGF were also detected in tissue homogenates from preg nant mares using I-125-labelled human EGF. Binding was high in the fet al membranes (allantochorion), both before implantation (days 30-34) a nd in the fully developed placenta (days 150-250), and was equivalent to the level of binding to homogenates of adult liver and kidney. Bind ing was much reduced in endometrial homogenates before implantation an d from non-pregnant mares but increased after implantation to reach va lues equivalent to those exhibited by the fetal membranes. Scatchard a nalysis of displacement curves indicated a single class of high-affini ty binding sites in the fetal membranes and pregnant endometrium sampl ed at day 150 of pregnancy and chemical cross-linking of the receptor -I-125-labelled EGF complexes in fetal membranes revealed two radiolab elled bands of 170 kDa and 150 kDa. A large excess of insulin-like gro wth factor I (IGF-I) failed to displace any labelled EGF from the tiss ue homogenates. The marked and sustained upregulation of endometrial E GF expression during pregnancy in mares, and the presence of EGF recep tors in the fetal allantochorion and maternal endometrium, suggest a p ossible role for EGF in the marked growth of these two tissues during placentation in equids.