the placenta forms a maternal-fetal junction that supports many physiological functions such as the supply of nutrition and exchange of gases and wastes. establishing an in vitro culture model of human and non-human primate trophoblast stem/progenitor cells is important for investigating the process of early placental development and trophoblast differentiation. In this study, we have established five trophoblast stem cell (TSC) lines from cynomolgus monkey blastocysts, named macTSC #1-5. Fibroblast growth factor 4 (FGF4) enhanced proliferation of macTSCs, while other exogenous factors were not required to maintain their undifferentiated state. macTSCs showed a trophoblastic gene expression profile and trophoblast-like DNA methylation status and also exhibited differentiation capacity towards invasive trophoblast cells and multinucleated syncytia. in a xenogeneic chimera assay, these stem cells contributed to trophectoderm (TE) development in the chimeric blastocysts. macTSC are the first primate trophoblast cell lines whose proliferation is promoted by FGF4. These cell lines provide a valuable in vitro culture model to analyze the similarities and differences in placental development between human and non-human primates.The placenta is an organ that forms a maternal-fetal junction and carries out various physiological functions such as facilitating the supply of nutrition to the fetus, exchange of gases, and removal of wastes from the fetus. In human and non-human primates, this multifunctional organ is characterized by the presence of three major placenta-specific cell-types, including proliferative cytotrophoblasts (CTBs), multinucleated syncytiotrophoblasts (STBs), and invasive extravillous trophoblasts (EVTs). CTBs include two different subtypes, villous CTBs and cell column trophoblasts. They are recognized as progenitor cell populations because villous CTBs and cell column trophoblasts differentiate into STBs and EVTs, respectively, during placentation 1,2 . When isolated and cultured in vitro, human CTBs cannot maintain an undifferentiated state and eventually differentiate into STBs 3 . Therefore, the establishment of an in vitro culture model for human and non-human primate trophoblast stem/progenitor cells is essential for investigating the process of early placental development and trophoblast differentiation in the primate.The HTR8/SVneo cell line, developed from primary EVTs, is a widely used model for human trophoblast in vitro; although, HTR8/SVneo cells express OCT4 and NANOG, the embryonic stem cell (ESC) markers 4,5 . In human blastocyst, OCT4 is detected in some cells of trophectoderm (TE), while the expression of NANOG is Trophoblast-like DNA methylation profile of macTSCs. Recently, Lee et al. proposed a criteria that involves hypomethylation of the ELF5 promoter to define human early trophoblast cells 22 . We also identified differentially methylated genomic regions, with higher methylation in the trophoblast cell lineage than in the embryonic cell lineage in mice and humans, and named such...
