An update on research into the enhanced regenerative mechanisms of lower animals: "Tiny wonders of the aquarium world, zebrafish can regenerate organs and tissues, including hearts, eye parts and fins. When a fin is lost, the fish regenerates a perfect copy in two weeks by orchestrating the growth of many tissue types, including bone, nerves, blood vessels, connective tissue and skin. ... In zebrafish, one or more microRNAs appear to be important to keep regeneration on hold until the fish needs new tissue ... In response to an injury, the fish then damp down levels of these microRNAs to aid regrowth. The team discovered that the ability of zebrafish to replace amputated fins is particularly sensitive to levels of a particular microRNA called miR-133. ... They probably need to have mechanisms to reduce the potential for unwelcome growth. The implication is that in order to make human tissue regenerate more effectively, we might want to look at some of these microRNAs as potential targets."