GRK5 and cardiac hypertrophy: However, TBX5, TBX20, ERBB4, and GRK5, which have been linked to the proliferation of fetal and neonatal cardiomyocytes [TBX5 (Misra et al., 2014; Maitra et al., 2009), TBX20 (Xiang et al., 2016; Chakraborty and Yutzey, 2012), ERBB4 (Bersell et al., 2009)] and cardiac hypertrophy [GRK5 (Gold et al., 2012; Traynham et al., 2015)], were upregulated in the CM1 cluster, as well as in Fetal cardiomyocytes.