In a recent study, it was found that African Spiny Mice (genus Acomys) could regenerate their kidneys after suffering damage to them. They could also regenerate their kidneys without having any dangerous or life-threatening scarring, as other animal species would.
It has been known for quite some time that Spiny Mice could regenerate basic tissues, such as their skin, when there was damage or removal of the tissue. This regeneration happens because of the inactivity or absence of the p21 gene. The p21 gene is a cell cycle inhibitor gene, and for a long time, was considered a tumor suppressor gene. It inhibits cyclin-dependent kinase and acts to prevent protein retinoblastoma phosphorylation by the inhibition of cyclin E/cdk2 complexes that are required for Rb phosphorylation.
However, when scientists damaged their kidneys, simulating kidney disease in the mice, they were able to regenerate and heal their tissue completely. This shows that the p21 gene can regulate regeneration in mammals with complex tissues and organs as well.