Yap1 safeguards mouse embryonic stem cells from excessive apoptosis during differentiation. Yap1 safeguards mouse embryonic stem cells from excessive apoptosis during differentiation

While Yap1, a Hippo pathway transcriptional effector, plays numerous roles in development and cancer, its functions in embryonic stem (ES) cell differentiation remain poorly characterized. It is known that approximately 30% of ES cells die after exiting self-renewal to differentiate, but upstream regulators of this process are not well known. We first observe that ES cells lacking Yap1 experience massive cell death upon the exit from self-renewal. We subsequently reveal that Yap1 contextually protects differentiating, but not self-renewing, mouse ES cells from hyperactivation of the apoptotic cascade. Mechanistically, Yap1 strongly activates anti-apoptotic genes via directly occupying their regulatory elements while mildly suppressing pro-apoptotic genes. Our demonstration of the pro-survival functions of Yap1 during ES cell differentiation expands our understanding of upstream regulators of the balance between survival and death during cell fate changes. Overall design: ChIP sequencing was performed for Yap1 in male mouse ES cells (strain J1). To perform ChIP-seq for Yap1, we generated Yap1-overexpressing FLAG/biotin-tagged clones, differentiated them for 3 days in ES- medium, and proceeded to formaldehyde-assisted crosslinking. Yap1 was pulled down along with associated DNA fragments using magnetic streptavidin-conjugated beads. ChIP-seq was also performed on BirA cells as a control, which express the BirA enzyme responsible for biotinylation, but do not overexpress any gene of interest.