Stem cells may help repair damaged 1) ___ after a heart attack. A study, done on mice, shows that stem cells play a limited, but significant role in 2) ___ damaged hearts. However, it remains unclear whether it is heart cells that are doing the repair, or cells from elsewhere in the 3) ___. Richard Lee and colleagues of the Harvard Medical School genetically engineered mice so their heart muscle cells could be stained with a fluorescent 4) ___. Around 80% of the heart 5) ___ cells in young mice picked up the stain. As the mice 6) ___, this level remained the same, which demonstrates that heart muscle cells are not normally replaced in life. However, when heart attacks were induced in the mice, the number of stained cells dropped to 70%, suggesting that new muscle cells are formed in response to injury. The study showed that the adult mouse 7) ___ has a limited ability to repair itself. The mechanism to activate cardiac 8) ___ is present, but it’s inadequate. This could be, because mammals don’t have enough [heart] stem cells? There are other theories as well. We need to understand what is holding the system back, so that we can devise a strategy to turn that brake off. Heart stem cells were first discovered last year. It’s not clear if this team has identified heart stem cells in the mice. Are they pre-existing immature cardiac muscle cells? Or are they [stem cells] from the heart or elsewhere in the body? Source: Nature Medicine (DOI: 10.1038/nm1618).

ANSWERS: 1) tissue; 2) repairing; 3) body; 4) protein; 5) muscle; 6) aged; 7) heart; 8) regeneration

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