mTOR activity paces human blastocyst stage developmental progression

Many mammals can temporally uncouple conception from parturition by pacing down their development around the blastocyst stage. In mice, this dormant state is achieved by decreasing the activity of the growth-regulating mTOR signaling pathway. It is unknown whether this ability is conserved in mammals in general and in humans in particular. Here we show that decreasing the activity of the mTOR signaling pathway induces human pluripotent stem cells (hPSCs) and blastoids to enter a dormant state with limited proliferation, developmental progression, and capacity to attach to endometrial cells. These in vitro assays show that, similar to other species, the ability to enter dormancy is active in human cells around the blastocyst stage and is reversible at both functional and molecular levels. The pacing of human blastocyst development has potential implications for reproductive therapies To test the effect of mTOR inhibition on the developmental timeline and morphology of human blastoids, these were first formed and then further cultured in the presence of the mTOR inhibitor RapaLink-1 and to test whether Rapalink-1 treated blastoids are reversible, we reactivated blastoids after 3 days of Rapalink-1 treatment and further cultured them on matrigel-coated plates.