Researchers in Italy have found microRNAs (miRNAs), tiny fragments of genetic material, that regenerate tissue in mouse hearts. The human heart isn't very good at repairing itself after something traumatic like a heart attack--it just replaces damaged heart cells with scar tissue that doesn't work as well. Two of the miRNAs set off nearly 2,000 genes to trigger growth of new heart cells in mice, reducing heart attack size and leading to recovery of the heart. This is an exciting breakthrough but it has its possible downside. Mauro Giacca of the International Centre for Genetic Engineering and Biotechnology told New Scientist that this could be a valuable therapeutic intervention after heart attacks in humans, as long as the miRNAs don't cause other kinds of cells to divide, possibly causing cancers. The miRNAs are currently delivered using viruses, and the next step is to create a synthetic version delivered in lipid envelopes. Press release | Article | Abstract