Ontogeny of elongation and gene expression in the early developing porcine conceptus

Early porcine conceptus development is characterized by rapid trophoblastic elongation between Days 11 and 12 of pregnancy, a period of embryonic loss in the pig. Growth factors and steroids secreted by the conceptus and uterus, as well as ligand receptors produced by the conceptus, are thought to regulate trophoblastic elongation. Therefore, the objectives of this study were to characterize conceptus gene expression for the steroidogenic enzymes 17alpha-hydroxylase and aromatase and the mesodermal marker brachyury, as well as the expression of receptors for fibronectin (integrin beta-1), progesterone, estrogen, oxytocin, prostaglandin F2alpha, and leukemia inhibitory factor (LIF), prior to and during trophoblastic elongation. Total RNA was extracted from individual conceptuses from Day 10 to Day 12 of pregnancy. Gene expression was determined by reverse transcription polymerase chain reaction on conceptuses having 2- to 4-, 5-, 6-, 7-, 8-, 9-, and 10- to 12-mm spherical, 13- to 25-mm tubular, and > 100-mm filamentous morphologies. There was a stage of development effect on both 17alpha-hydroxylase (p < 0.001) and aromatase (p < 0.003) gene expression. Initial 17alpha-hydroxylase gene expression was detected in early spherical conceptuses (2-4 mm), increasing abruptly through to 7-mm conceptuses. Aromatase gene expression increased dramatically in 6- to 7-mm conceptuses, with increased expression throughout development. Gene expression for LIF receptor (LIFR) (p < 0.02) was similar to that for 17alpha-hydroxylase, while brachyury gene expression began in 6-mm conceptuses and increased (p < 0.001) throughout development. Integrin beta-1 was expressed at all stages of development. Conceptus gene expression was not detected for progesterone, estrogen, oxytocin, and prostaglandin F2alpha receptors. Prior to elongation, dynamic changes in gene expression are occurring that appear to be associated with estrogen production and preparation of the conceptuses for elongation. LIFR expression is highly associated with steroidogenic enzyme production with an initial peak preceding rapid trophoblastic elongation, suggesting that LIF may be involved in early conceptus development in the pig.