WARS1 and glioblastoma: We found that efficient cardiac specification requires the tryptophanyl‐tRNA synthetase WARS1, a conserved transcriptional target of ATF4 also identified in mouse fibroblasts[55] and human glioblastoma cells.[56] Aminoacyl‐tRNA synthetases (ARSs) are essential enzymes for protein synthesis[57] and have not been previously implicated in ESC biology and heart development.