ZZZ3 protects human embryonic stem cells from nucleolar stress by boosting mTOR/ribosome pathway.

Embryonic stem cells (ESCs) are defined as stem cells with self-renewing and differentiation capabilities. These unique properties are tightly regulated and controlled by complex genetic and molecular mechanisms whose understanding is essential for both basic and translational research. A large number of studies have mostly focused on understanding the molecular mechanisms governing pluripotency and differentiation of ESCs, while the regulation of proliferation has received comparably less attention. In mouse ESCs, pluripotency and proliferation can be independent processes meaning that it is possible for mouse ESCs to maintain their pluripotent state without actively proliferating. Here, we investigate the role of ZZZ3 (Zinc Finger ZZ-Type Containing 3) function in human ESCs homeostasis. We found that knockdown of ZZZ3 strongly decreases ribosome biogenesis, translation, and mTOR signaling leading to nucleolar stress and significant reduction of cell proliferation. This process occurs without affecting pluripotency, suggesting that ZZZ3-depleted ESCs enter a dormant-like state and that proliferation and pluripotency can be uncoupled also in human ESCs.