124 THE MAJOR GENE EXPRESSION PATTERNS IN ENDOMETRIAL TISSUE OF PIGS DURING EARLY GESTATION

Abstract

Although the expression of important genes in the embryo at pre-implantation stage, which encompasses the period from fertilization to implantation, have been reported for mice and cows, little information relevant to this subject is known in pigs. The objective of this study was to investigate the changes of importantly expressed genes and proteins in endometrial tissue of pigs from fertilization to implantation. Six genes, including estrogen receptor-α, estrogen receptor-β, LIF, LR (LIF receptor), TGFβ1, and TGFβ2, that may play important roles in regulating uterine receptivity and successful implantation and that show different expression patterns by the stages of pregnancy were selected. As a step toward understanding the role of gene and protein expression changes in endometrial tissue of pigs during the preimplantation stage (Day 2, Day 6, Day 8, Day 12, and Day 17, n = 3/group) and the post-implantation stage (Day 21 and Day 33, n = 3/group) and Day 0 (estrous), real-time PCR methods for quantitative analysis of genes and immunohistochemistry methods to localize protein expression were utilized. Data from quantitative real-time PCR were analyzed by ANOVA. The results of this experiment indicated that estrogen receptor-β mRNA level was sharply increased to Day 12 of pregnancy, while estrogen receptor-α mRNA did not change drastically during early pregnancy stage. In contrast, levels of LIF and LR mRNA were increased from Day 2 to Day 33. Although TGFβ1 mRNA reached peak on Day 17 and TGFβ2 mRNA showed the highest level on Day 17, TGFβ2 did not appear to change drastically. For the protein expression patterns, estrogen receptor-α and estrogen receptor-β proteins were expressed in both luminal epithelium and glandular epithelium, but they were only partially expressed in some tissues of stroma cells. LIF protein was expressed in all cell types, while TGF β1 protein was high expressed in glandular epithelium. Also, ERs, LIF, and TGF β1 mRNA and protein expression showed stage- and cell-specific expression patterns. We also investigated the gene expression of TGF β1 mRNA and TGF β2 mRNA in early conceptus (Day 12 and Day 17). TGF β1 mRNA expression was low in Day 12 embryos, and increased progressively to Day 17. This indicated that both the maternal uterus and the conceptus represent the same gene expression pattern. These results suggest that estrogen receptor-β could be an important factor in estrogen action in endometrial tissue during early gestation in pigs, and TGF βs function in both autocrine and paracrine interactions. Progressive increase in TGF β1 mRNA expression in conceptus and uterine tissues suggest important roles of TGF β1 in conceptus development and establishment of the uterine receptivity during the peri-implantation period.