When a person has a heart attack, the heart repairs its damaged
muscle by forming scar tissue. As a result, the heart never
truly goes back to the way it was. But when a zebrafish has a
heart injury, like having a large chunk of it chopped off, it
grows a brand new piece to replace it. Two independent reports
published in the journal Nature show that within days of an
injury to its heart, the zebrafish has the remarkable ability to
regenerate most of the missing cardiac tissue using mature heart
cells–not stem cells, as some researchers had suspected. The
findings help explain why human beings can’t regenerate a heart
or missing limbs. The reports contradict a previous study (pdf)
done by one of the research teams in 2006 that suggested that
stem cells, the general all-purpose cells that develop into all
the mature and functional cells of the body, were responsible
for self-repair. The finding suggest that doctors have been on
the wrong track with recent stem cell-based therapies for heart
attack patients. Ma