Cellular systems biology identifies dynamic trophoblast populations in early human placentas

The human placenta is accessible in early developmental stages and affords a unique opportunity to investigate human organogenesis and the dynamics of transitory cell populations in human placenta development.

The cell surface proteomic profile of early trophoblast cells of first trimester human placentas was quantified using a high throughput flow cytometry screen of 370 Cluster of Differentiation (CD) antigens. Targeted investigation of candidate trophoblast progenitor populations was done through immunohistochemistry, multi-color flow cytometry, and genome wide expression analysis.

Using a novel batch correction and normalization methodology, we identified 23 increasing and 13 decreasing markers of dynamic populations between the week 6 and week 10 of placenta development. We identified and characterized two transient populations expressing either EpCAM (CD326) or CDCP1 (CD318). Immunohistochemistry revealed these CD antigens are expressed by discrete cells with EpCAM localized to the proximal villi columns and CDCP1 to distal columns. Flow analysis confirmed independence of these populations and identified EpCAM cells as positive for EGFR. Microarray analysis indicated EpCAM+/EGFR+ and EFGR + cells showed high degree of gene expression similarities to villus cytotrophoblast but loss of EpCAM expression was concomitant with exit from the cell cycle. Similarly, CDCP1 positive trophoblast are enriched in cell cycle gene sets and expressed genes with significant similarity to extravillous cytotrophoblast.

Our study indicates at least two distinct subpopulations of cytotrophoblasts exist in the early first trimester within the column that likely maintains pools of actively dividing progenitor cells giving rise to the developing placenta villous tree.