SLC20a1/PiT-1 is required for chorioallantoic placental morphogenesis.

The placenta mediates transport of nutrients, such as inorganic phosphate (Pi), between the maternal and fetal circulatory systems. The placenta itself also requires high levels of nutrient uptake as it develops, to provide critical support for fetal development. This study aimed to determine placental Pi transport mechanisms using in vitro and in vivo models. We observed that Pi (P33) uptake in BeWo cells is sodium-dependent, and that SLC20A1/Slc20a1 is the most highly expressed placental sodium-dependent transporter in mouse (microarray) and human cell line (RT-PCR) and term placenta (RNA-seq), supporting that normal growth and maintenance of the mouse and human placenta requires SLC20A1/Slc20a1. Slc20a1 wildtype (Slc20a1+/+) and knockout (Slc20a1-/-) mice were produced through timed intercrosses, and displayed yolk sac (YS) angiogenesis failure as expected at E10.5. E9.5 tissues were analyzed to test whether placental morphogenesis requires Slc20a1. At E9.5 the developing placenta was reduced in size in Slc20a1-/-. Multiple structural abnormalities were also observed in the Slc20a1-/- chorioallantois. We determined that MCT1+ cells were reduced in developing Slc20a1-/- placenta, confirming that Slc20a1 loss reduced trophoblast syncytiotrophoblast 1 (SynT-I) coverage. Next, we examined cell type-specific Slc20a1 expression and SynT molecular pathways in silico, and identified Notch/Wnt as a pathway of interest that regulates trophoblast differentiation. We further observed that specific trophoblast lineage express Notch/Wnt genes that associate with endothelial cell tip-and-stalk cell markers. In conclusion, our findings support that Slc20a1 mediates symport of Pi into SynT cells, providing critical support for their differentiation and angiogenic mimicry function at the developing maternal-fetal interface.