mTor inhibition induces a paused pluripotent state

Cultured pluripotent stem cells are a cornerstone of regenerative medicine due to their ability to give rise to all cell types of the body. While pluripotent stem cells can be propagated indefinitely in vitro, pluripotency is paradoxically a very transient state in vivo, lasting 2-3 days around the time of blastocyst implantation. The exception to this rule is embryonic diapause, a reversible state of suspended development triggered by unfavorable conditions. Diapause is a strategy widely employed across the animal kingdom, including in mammals, but its regulation remains poorly understood. Here we report that inhibition of mechanistic target of rapamycin (mTor), a major nutrient sensor and promoter of growth, induces reversible pausing of mouse blastocyst development and allows their prolonged culture ex vivo. Paused blastocysts remain pluripotent and competent to give rise to embryonic stem (ES) cells and mice. We show that both natural diapause blastocysts in vivo and paused blastocysts ex vivo display pronounced reductions in mTor activity, translation and transcription. In addition, pausing can be induced directly in cultured ES cells and sustained for weeks in the absence of cell death or deviations from cell cycle distributions. We show that paused ES cells remain pluripotent, display a remarkable global suppression of transcription, and maintain a gene expression signature of diapaused blastocysts. These results allow for the first time the sustained suspension of development of a mammalian embryo in the laboratory, and shed light on the regulation of diapause and the origins of ES cells. Our findings have important implications in the fields of assisted reproduction, regenerative medicine, cancer, metabolic disorders and aging. Examination of RNA expression profiles of embryonic stem cells in serum, 2i and paused states by RNA-seq