Molecular pathways of phagocytosis and invasion in the developing chorionic girdle

Abstract

The chorionic girdle trophoblast of the equine conceptus is a rapidly developing tissue that undergoes dynamic modifications in gene and protein expression between days 30 and 36 post conception. We employed a 15,000 element custom gene expression microarray to identify transcripts differentially expressed between invasive (chorionic girdle) and non-invasive (chorion) trophoblast at day 34 post conception. One of the genes that showed dramatic up regulation in chorionic girdle compared to chorionwas ELMO1, which encodes amember of the Engulfment and Cell Motility protein family. ELMO1 is an intracellular protein that has been shown to be involved in phagocytosis and cell invasion in normal cells and in tumors. Both of these functions are important in chorionic girdle as the cells migrate into the endometrium to form the endometrial cups. Quantitative Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR) was used to evaluate ELMO1 expression in fetal and placental tissues. Temporal studies of samples ranging from day 15 trophectoderm to day 43 endometrial cups demonstrated that ELMO1 was expressed only in chorionic girdle cells, with rapid increases between days 32 and 35, followed by decreased expression in early endometrial cups. The spatial distribution of ELMO1 at day 34 was also striking; ELMO1 was expressed highly only in chorionic girdle (approx. 5,000 transcripts per 10ng of RNA), and not in chorion,