It is critical to specify a signal that directly drives the transition that occurs between cell states. However, such inferences are often confounded by indirect intercellular communications or secondary transcriptomic changes due to primary transcription factors. Although FGF is known for its importance during mesoderm-to-endothelium differentiation, its specific role and signaling mechanisms are still unclear due to the confounding factors referenced above. Here, we attempted to minimize the secondary artifacts by manipulating FGF and its downstream mediators with a short incubation time before sampling and protein-synthesis blockage in a low-density angioblastic/endothelial differentiation system. In less than 8 h, FGF started the conversion of KDR^low/PDGFRA^low nascent mesoderm into KDR^high/PDGFRA^low angioblasts, and the priming by FGF was necessary to endow endothelial formation 72 h later. Further, the angioblastic conversion was mediated by the FGFR1/BRAF/MEK/ERK pathway in mesodermal cells. Finally, two transcription factors, ETV2 and LMO2, were the early direct functional responders downstream of the FGF pathway, and ETV2 alone was enough to complement the absence of FGF. FGF’s selective role in mediating the first-step, angioblastic conversion from mesoderm-to-endothelium thus allows for refined control over acquiring and manipulating angioblasts. The noise-minimized differentiation/analysis platform presented here is well-suited for studies on the signaling switches of other mesodermal-lineage fates as well.

指定直接驱动细胞状态之间发生的转换的信号至关重要。然而，此类推论常常被间接细胞间通讯或初级转录因子引起的次级转录组变化所混淆。尽管 FGF 因其在中胚层向内皮分化过程中的重要性而闻名，但由于上述混杂因素，其具体作用和信号传导机制仍不清楚。在这里，我们试图通过在低密度成血管细胞/内皮分化系统中采样前短的孵育时间和蛋白质合成阻断来操纵 FGF 及其下游介质，从而最大程度地减少次生伪影。在不到8小时内，FGF开始将KDR^低/PDGFRA^低新生中胚层转化为KDR^高/PDGFRA^低成血管细胞，并且FGF的启动对于72小时后赋予内皮形成是必要的。此外，成血管细胞转化是由中胚层细胞中的 FGFR1/BRAF/MEK/ERK 通路介导的。最后，两个转录因子 ETV2 和 LMO2 是 FGF 通路下游的早期直接功能反应因子，仅 ETV2 就足以补充 FGF 的缺失。 FGF 在介导从中胚层到内皮的第一步成血管细胞转化中的选择性作用因此允许对获取和操纵成血管细胞进行精细控制。这里提出的噪声最小化分化/分析平台也非常适合研究其他中胚层谱系命运的信号开关。