Females' regenerating advantage

M en might build more muscle, but women are better at keeping what they have, if results from Deasy et al. (page 73) are any indication. The group shows that female muscle stem cells are better than their male counterparts at regenerating lost muscle. The authors were led into the realm of muscle and sex when they realized that they were relying heavily on cell lines derived from female mice to study muscle regen-eration. Most of the male lines, by contrast, were stuck away in the freezer. They supposed that the female ones were more popular because they were working better. The group now shows that female muscle stem cells are indeed better at regenerating diseased muscle in a mouse model. While the male cells proliferated briefl y and abruptly differentiated into muscle, the female cells held out. They proliferated more slowly at fi rst, but cycled longer before becoming muscle. By multiplying fi rst, the stem cells can eventually create more fi bers. The female cells also seem better equipped to deal with the hypoxic conditions and reactive oxygen species found in injured and diseased muscle, as they up-regulated more stress-related and antiapoptotic genes. Artifi cially turning on antiapoptotic Bcl-2 in male stem cells was not enough to improve their regeneration, however. Hormones may also have some infl uence, as females were better recipients as well as donors. But estrogen treatments did not prod stem cells of either sex to make muscle more effi ciently. The authors still need to determine the ultimate cause of the female cells' superior regenerating ability. Perhaps a Y chromosome gene encourages quick differentiation. Whatever the cause, biologists should make sure to note cell sex when describing their experimental methods with stem cells of any sort. Notch remodels junctions T he Notch pathway is renowned for its reign over differentiation. Now, its sway is widened into the realm of morphogenesis and cell–cell adhesion. Grammont (page 139) shows that Notch signaling remodels adherens junctions while cells change shape during development. Developmental programs generally require plenty of changes in cell shape. In the developing fl y oocyte, a set of cells on the posterior end acquire a co-lumnar shape, whereas anterior cells fl at-ten. Notch has been implicated in several aspects of oogenesis in fl ies. To better dissect its role, Grammont analyzed developing oocytes with somatic clones mutant for Notch signaling. The clones revealed that …