Specifying the Anterior Primitive Streak by Modulating YAP1 Levels in Human Pluripotent Stem Cells

Specifying the primitive streak (PS) guides stem cell differentiation in vitro, however much remains to be learned about the transcription networks that direct anterior and posterior PS cells (APS and PPS, respectively) to differentiate to distinct mesendodermal subpopulations. Here, we show that APS genes are predominantly induced in YAP1-/- hESCs in response to ACTIVIN. This finding establishes the Hippo effector YAP1 as a master regulator of PS specification, functioning to repress ACTIVIN-regulated APS genes in hESCs. Moreover, transient exposure of wild-type hESCs to dasatinib, a potent C-SRC/YAP1 inhibitor, enables differentiation to APS-derived endoderm and cardiac mesoderm in response to ACTIVIN. Importantly, these cells can differentiate efficiently to normal beating cardiomyocytes without the cytoskeletal defect seen in YAP1-/- hESC-derived cardiomyocytes. Overall, we uncovered an induction mechanism to generate APS cells using a cocktail of ACTIVIN and YAP1i molecules that holds practical implications for hESC and iPSC differentiation into distinct mesendodermal lineages.原条（primitive streak, PS）的特化可指导干细胞的体外分化，但目前针对引导前原条细胞（APS）与后原条细胞（PPS）分化为不同中内胚层亚群的转录调控网络，仍有诸多科学问题有待解析。本研究发现，在激活素（ACTIVIN）刺激下，APS相关基因主要在YAP1基因敲除的人类胚胎干细胞（human embryonic stem cells, hESCs）中被诱导表达。该结果确立了Hippo通路效应因子YAP1作为PS特化的核心调控因子，其在人类胚胎干细胞中可抑制激活素介导的APS相关基因表达。此外，对野生型人类胚胎干细胞进行短暂的达沙替尼（dasatinib，一种强效C-SRC/YAP1抑制剂）处理，可使其在激活素诱导下分化为APS来源的内胚层与心脏中胚层。尤为重要的是，这些细胞可高效分化为正常搏动的心肌细胞，且未出现YAP1基因敲除人类胚胎干细胞来源心肌细胞所存在的细胞骨架缺陷。综上，本研究揭示了一种通过激活素与YAP1抑制剂（YAP1i）组合诱导生成APS细胞的机制，该机制在人类胚胎干细胞及诱导多能干细胞（induced pluripotent stem cell, iPSC）定向分化为不同中内胚层谱系的研究中具有实际应用价值。