Chemical conversion of human conventional PSCs to TSCs following transient naive gene activation

Abstract

In human embryos, naive pluripotent cells of the inner cell mass (ICM) generate epiblast, primitive endoderm and trophectoderm (TE) lineages, whence trophoblast cells derive. In vitro , naive pluripotent stem cells (PSCs) retain this potential and efficiently generate trophoblast stem cells (TSCs), while conventional PSCs form TSCs at low efficiency. Transient histone deacetylase and MEK inhibition combined with LIF stimulation is used to chemically reset conventional to naive PSCs. Here, we report that chemical resetting induces the expression of both naive and TSC markers and of placental imprinted genes. A modified chemical resetting protocol allows for the fast and efficient conversion of conventional PSCs into TSCs, entailing shutdown of pluripotency genes and full activation of the trophoblast master regulators, without induction of amnion markers. Chemical resetting generates a plastic intermediate state, characterised by co‐expression of naive and TSC markers, after which cells steer towards one of the two fates in response to the signalling environment. The efficiency and rapidity of our system will be useful to study cell fate transitions and to generate models of placental disorders. image Chemical resetting allows the fast and rapid conversion of conventional pluripotent stem cells (PCGs) into bona fide trophoblast stem cells (TSCs) through a plastic intermediate state, characterized by the co‐expression of naive and TSC markers. Several placental, trophectoderm, and trophoblast markers are activated during chemical resetting of conventional PSCs. Transient HDAC and MEK inhibition combined with LIF stimulation and exposure to TSC medium converts conventional PSCs to TSCs. Chemically converted TSCs (ccTSCs) are bona fide TSCs that have the potential to differentiate into STBs and EVTs.