Using gene-edited, glow-in-the-dark salamanders, the scientists parsed out the important role of a chemical called retinoic acid, a form of vitamin A and also the active ingredient in the acne medicine isotretinoin (commonly known as Accutane). “I really think that we’ll be able to figure out how to regenerate human limbs,” McCusker says. Then, they used a drug to tamp down naturally occurring retinoic acid levels, and observed the effects on regenerating limbs. CYP26b1 breaks down retinoic acid, so when the gene that makes the protein is activated, retinoic acid concentrations drop, allowing the conditions for foot and digit formations. Other scientists, McCusker included, have also made big recent strides in attempting to unlock limb regeneration.