Spatial and temporal analyses of integrin and Muc-1 expression in porcine uterine epithelium and trophectoderm in vivo

The spatial and temporal expressions of Muc-1, selected integrin subunits, and extracellular matrix components in porcine uterine epithelium from estrous (Days 0, 4, 8, 10-15) and early pregnant (Days 10-15 of pregnancy) gilts and from steroid-treated ovariectomized gilts were analyzed using indirect immunofluorescence analyses on cryosectioned tissues to identify potential components of uterine receptivity. Integrin subunit and extracellular matrix expressions were also examined in Day 11-15 conceptuses. Intense Muc-1 staining was detected on apical uterine epithelium on Day 0 but was absent by Day 10 in both cyclic and pregnant gilts. The result of estrogen treatment (E(2); 100 mu g/day for 10 days) was similar to that of the corn oil vehicle control, while treatment with progesterone (P-4; 200 mg/day for 10 days) or E(2)+P-4 decreased Muc-1 staining in ovariectomized gilts. Immunostaining performed with antibodies directed against integrin subunits (alpha(1), alpha(3), alpha(4), alpha(5), alpha(v), beta(1), and beta(3)) in uterine epithelium revealed low (integrin subunits alpha(1) and alpha(3)), high (integrin subunits alpha(v) and beta(3)), or modulated (integrin subunits alpha(4), alpha(5), and beta(1)) expression, with the lowest expression on Day 0 and maximum expression by Days 10-15. Additionally, no differences due to pregnancy status were detected in staining of uterine epithelium on Days 10-15. Uterine epithelium from steroid-treated ovariectomized gilts had low expression of alpha(4), alpha(5), and beta(1) subunits in the presence of E(2) that increased in response to P-4 and E(2)+P-4 treatments. The expression of integrin subunits alpha(3), alpha(v), and beta(3) was not affected by sex steroids. Trophectoderm also expressed alpha(1), alpha(4), alpha(5), alpha(v), beta(1), and beta(3) integrin subunits. Extracellular matrix constituents (fibronectin, vitronectin, laminin, and collagen type IV) were also examined. Fibronectin and vitronectin were present on trophectoderm, but only vitronectin was detected on uterine epithelium. The alpha(4), alpha(5), alpha(v), beta(1), and beta(3) integrin subunits, vitronectin, and fibronectin were detected at sites of attachment between uterine epithelial cells and trophectoderm on Days 12-15 of pregnancy. These studies indicate that down-regulation of Muc-1 coincides with the transition of the prereceptive uterus to the receptive uterus. Additionally, the expression of alpha(4), alpha(5), alpha(v), beta(1), and beta(3) integrin subunits along with the extracellular matrix components of fibronectin and vitronectin correlates with the time of implantation in swine.