Heart stem cells isolated

Two local research groups today report the isolation of two types of heart stem cells that together give rise to all three main tissue types in the heart.

The cells can mature into cardiac muscle tissue and can also turn into the cells that make up the smooth muscle tissue and the heart’s blood vessels. The discovery changes current ideas about how the heart forms and brings researchers one step closer to the use of stem cell therapy to repair heart tissue.

Researchers have wondered whether the different parts of the heart grow from different stem cells that come together during early embryonic development, or whether one local stem cell generates all the tissues in the organ. The finding that one cell can initiate the whole program could simplify the repair of damaged heart tissue; replacement of one master cell type may be sufficient to mend muscle, blood vessels, and the heart’s pacemaker cells.

Kenneth Chien of Massachusetts General Hospital and collaborators identified the precursor cells in the embryonic mouse heart and showed that they grew into muscle or blood vessel cells. The team then produced the stem cells in the lab from embryonic stem cell cultures. If human cells behave in the same way, this could provide a source of stem cells for transplants.

Another group, led by Stuart Orkin at Children’s Hospital Boston, independently identified a slightly different stem cell in mice that could form either cardiac or smooth muscle cells, but did not appear to give rise to blood vessel cells.

It’s not clear yet how the two types of stem cells are related, but the researchers hope to work that out soon. The first author on Orkin’s paper, Sean Wu, has accepted a position in Chien’s Cardiovascular Research Center at MGH. Both Chien and Orkin are also affiliated with the Harvard Stem Cell Institute.

The two papers appear today in the online edition of Cell.

Battle of the sexes reversed in fruit flies by gene swap

Edward Kravitz of Harvard Medical School has spent the last five years watching fruit flies fight, with the aim of figuring out how genes control aggressive behaviors. He’s found that males and females forced to fight over food have vastly different pugilistic styles. Females usually butt and shove, while males prefer to lunge and box.

That difference is hardwired into the fly genome, according to the latest results from Kravitz’s fruit fly fight club. Collaborating with researchers at the Institute of Molecular Pathology in Vienna, the Harvard researchers have shown that swapping just one gene between males and females completely altered the flies’ fighting styles.

Male flies with the female version of the gene tended to pick fights with females and to be less aggressive with other males. When fighting, they showed more head butting and shoving and none of the boxing behavior favored by normal males. Conversely, when females carried the male version of the gene, they displayed far more aggressive fighting styles.

Trading the gene caused the flies some confusion in the romantic realm as well. Male flies with the female gene tended to fight with females rather than court them, and female flies with the male gene courted other females and fended off males.

This result is in keeping with previous studies that implicated the gene, called fruitless, in sex-specific mating behavior. By watching flies fight and mate with each other, researchers are hoping to figure out the neuronal circuitry behind these opposing instincts.

Their paper appeared this week in Nature Neuroscience online.