Cytotrophoblasts

Cytotrophoblasts are a population of mononuclear trophoblastic cells that form the proliferative inner layer of the chorionic villi in the placenta. They originate from the trophectoderm of the blastocyst and function as the stem cell pool for the placental trophoblast lineages.

During placental development, cytotrophoblasts proliferate and differentiate along two main pathways: fusion with neighboring cytotrophoblasts to create the multinucleated syncytiotrophoblast, which covers the villous surface and mediates nutrient and gas exchange, and directed invasion to form extravillous cytotrophoblasts that migrate into the maternal decidua and contribute to remodeling of spiral arteries.

Structurally, cytotrophoblasts are mononuclear cells located beneath the syncytiotrophoblast. They express epithelial markers such as cytokeratins and act as progenitors for the syncytiotrophoblast and extravillous trophoblast lineages; the latter express specialized markers, including HLA-G, during invasion.

Clinically, abnormal cytotrophoblast invasion or proliferation is associated with placental pathologies such as preeclampsia and intrauterine growth restriction. Choriocarcinoma can arise from trophoblastic cells, including the cytotrophoblast lineage.