LAUSR

What is the central question of this study? What is the role of fibrinogen‐like protein 2 (FGL2) in murine cardiomyocyte maturation? What is the main finding and its importance? This is the first study showing both global Fgl2 knockout and cardiac‐specific FGL2 deletion trigger early death and dilated cardiomyopathy. By using an adeno‐associated virus (AAV)‐mediated CRISPR/Cas9‐based somatic mutagenesis system, it was demonstrated that cardiac‐specific FGL2 depletion induces ventricular dilatation and remodelling, and disrupts the normal hypertrophic growth and polyploidization of cardiomyocytes. In addition, it was shown that modulation of signal transducer and activator of transcription 3, extracellular signal‐regulated kinases 1 and 2 and fibroblast growth factor 2 signalling is associated with loss‐of‐FGL2‐mediated cardiac dysfunction. These results suggest FGL2 is an important determinant of cardiomyocyte maturation.