Expression of insulin-like growth factor (IGF) family members in porcine pregnancy

Prenatal mortality is a prime concern for commercial swine industry in North America. Fetal losses occur throughout gestation but cluster in early (~day20) and mid (~day50) pregnancy. Adequate vascularization of the attachment site has emerged as a key factor contributing to fetal success. Since Insulin-Like Growth Factor (IGF) family members regulate angiogenesis in addition to promoting fetal development and growth, we hypothesized that conceptus success is governed by members of the IGF family. Using quantitative real time PCR, we analyzed expression of IGF family members (IGF-I, IGF-II, IGF-I Receptor (IGF-IR), IGF-IIR and their binding proteins, IGFBPs) in matched maternal and fetal tissues of healthy and arresting conceptuses at gestation days (gd) 20 and 50. IGF-II transcripts were 100 fold increased in both maternal and fetal tissues compared to IGF-I, but receptor transcripts were found in similar abundance irrespective of health status and gestation point. IGFBP3 was the most abundantly transcribed of the binding proteins. Using immunohistochemistry we confirmed the expression of IGF family members in maternal luminal and glandular epithelial cells, the endothelium of blood vessels and some scattered stromal cells. Our results suggest that IGF-I and II and their receptors are differentially expressed at the maternal and fetal components of the attachment site.