Juvenile zebrafish heart
In contrast to humans, zebrafish can regenerate heart muscle after an injury. When the zebrafish heart is injured, the muscle cells in the heart, called cardiomyocytes, begin to proliferate and give rise to new heart cells. Shoffner et al. show that levels of a gene called Mdm2 sharply increase in zebrafish cardiomyocytes after heart injury. Mdm2 regulates a protein called Tp53, and they showed that if zebrafish lose Tp53 function then the proliferation of cardiomyocytes is enhanced during regeneration. They also showed that if the function of Mdm2 is impaired, it has the opposite effect. This study suggests that Mdm2 has a broad role in cardiogenesis because it is turned on during heart regeneration and is associated with markers of de-differentiation after heart injury.