Analysis and characterization of differential gene expression during rapid trophoblastic elongation in the pig using suppression subtractive hybridization

During late peri-implantation development, porcine conceptuses undergo a rapid (2-3 hrs) morphological transformation from a 10 mm sphere to a thin filamentous form greater than 150 mm in length. Elongation of the conceptus is important for establishing adequate placental surface area needed for embryo and fetal survival throughout gestation. Genes involved with triggering this unique transition in conceptus development are not well defined. Objective of the present study was to utilize suppression subtractive hybridization (SSH) to characterize the change in gene expression during conceptus transformation from spherical (8-9 mm) to tubular (15-40 mm) to early filamentous (>150 mm) morphology. Spherical, tubular, and filamentous conceptuses were collected from pregnant gilts and subjected to SSH. Forward and reverse subtractions were performed to identify candidate genes differentially expressed during spherical to tubular and tubular to filamentous transition. A total of 384 transcripts were differentially screened to ensure unique expression. Of the transcripts screened, sequences were obtained for 142 that were confirmed to be differentially expressed among the various morphologies. Gene expression profiles during rapid trophoblastic elongation were generated for selected mRNAs using quantitative real-time PCR. During the transition from tubular to early filamentous conceptuses, s-adenosylhomocysteine hydrolase and heat shock cognate 70 kDa expression were significantly enhanced. A novel unknown gene was isolated and shown to be significantly up-regulated at the onset of rapid trophoblastic elongation and further enhanced in filamentous conceptuses.