Derivation of Haploid Trophoblast Stem Cells via Conversion In Vitro.

Owing to their single genome, haploid cells are powerful to uncover unknown genes by performing genetic screening in mammals. However, no haploid cell line from an extraembryonic lineage has been achieved yet, which limits the application of haploid cells in placental genetic screening. Here, we show that overexpression of Cdx2 can convert haploid embryonic stem cells to trophoblast stem cells (TSCs). p53 deletion reduces diploidization during the conversion and guarantees the generation of haploid-induced TSCs (haiTSCs). haiTSCs not only share the same molecular characterization with trophoderm-derived TSCs but also possess multipotency to placental lineages in various procedures. In addition, haiTSCs can maintain haploidy in the long term, assisted by periodic sorting and with reliance on FGF4 and heparin. Finally, we perform piggyBac-mediated high-throughput mutation in haiTSCs and use them in trophoblast lineage genetic screening. Deep sequencing analysis and validation experiments prove that Htra1 is a blocker for spongiotrophoblast specification.