Primitive endoderm stem cell lines in mice

A blastocyst consists of three distinctive cell types: epiblast (EPI), trophoblast (TB), and primitive endoderm (PrE). Stem cell lines representing EPI and TB (embryonic stem (ES) cells and trophoblast stem (TS) cells) have been derived and they contribute to epiblast derivatives and trophoblast derivatives of stem cell-blastocyst chimeras, respectively. Although derived from PrE, extraembryonic endoderm (XEN) cells contribute to only a limited part of parietal endoderm (PE) but rarely to other PrE derivatives. Here we describe the establishment of primitive endoderm stem (PrES) cell lines in mice. PrES cells were derived and maintained in a serum-free media containing CHIR99021, FGF4, heparin, and PDGF-AA. RNA-seq analysis revealed that the transcriptome of PrES cells is globaly different from XEN cells: PrES cells express not only endoderm markers (Dab2, Gata4, Gata6, Sox17, etc.), but also pluripotent markers (Pou5f1, Cdh1, Nanog, Zfp42, etc.), and resembles in vivo founder PrE. PrES cells were rapidly and efficiently incorporated into PrE after blastocyst injection and efficiently contributed to all PrE derivatives, including PE, VE (visceral endoderm), and MZE (marginal zone endoderm) in chimeras. Importantly, PrES cells rescued embryonic lethality of PrE-depleted blastocysts by complementing all PrE derivatives. PrES cells thus not only contribute to understanding of the mechanisms of PrE specification but also provide a critical resource for artificial embryo reconstitution by stem cells alone. Overall design: mRNAs were extracted from ES, TS, XEN and PrES stem cell