Segmentation in vertebrates first arises when the unsegmented paraxial mesoderm subdivides to form paired epithelial spheres called somites. The Notch signalling pathway is important in regulating the formation and anterior-posterior patterning of the vertebrate somite. One component of the Notch signalling pathway in Drosophila is the fringe gene, which encodes a secreted signalling molecule required for activation of Notch during specification of the wing margin. Here we show that mice homozygous for a targeted mutation of the lunatic fringe (Lfng) gene, one of the mouse homologues of fringe, have defects in somite formation and anterior-posterior patterning of the somites. Somites in the mutant embryos are irregular in size and shape, and their anterior-posterior patterning is disturbed. Marker analysis revealed that in the presomitic mesoderm of the mutant embryos, sharply demarcated domains of expression of several components of the Notch signalling pathway are replaced by even gradients of gene expression. These results indicate that Lfng encodes an essential component of the Notch signalling pathway during somitogenesis in mice.
It is widely postulated that tissue aging could be, at least partially, caused by reduction of stem cell number, activity, or both. However, the mechanisms of controlling stem cell aging remain largely a mystery. Here, we use Drosophila ovarian germline stem cells (GSCs) as a model to demonstrate that age-dependent decline in the functions of stem cells and their niche contributes to overall stem cell aging. BMP signaling activity from the niche significantly decreases with age, and increasing BMP signaling can prolong GSC life span and promote their proliferation. In addition, the age-dependent E-cadherin decline in the stem cell-niche junction also contributes to stem cell aging. Finally, overexpression of SOD, an enzyme that helps eliminate free oxygen species, in either GSCs or their niche alone can prolong GSC life span and increase GSC proliferation. Therefore, this study demonstrates that stem cell aging is controlled extrinsically and intrinsically in the Drosophila ovary.
Atomically dispersed transition metals confined with nitrogen on a carbon support has demonstrated great electrocatalytic performance, but an extremely low concentration of metal atoms (usually below 1.5%) is necessary to avoid aggregation through sintering which limits mass activity. Here, a salt‐template method to fabricate densely populated, monodispersed cobalt atoms on a nitrogen‐doped graphene‐like carbon support is reported, and achieving a dramatically higher site fraction of Co atoms (≈15.3%) in the catalyst and demonstrating excellent electrocatalytic activity for both the oxygen reduction reaction and oxygen evolution reaction. The atomic dispersion and high site fraction of Co provide a large electrochemically active surface area of ≈105.6 m2 g−1, leading to very high mass activity for ORR (≈12.164 A mgCo−1 at 0.8 V vs reversible hydrogen electrode), almost 10.5 times higher than that of the state‐of‐the‐art benchmark Pt/C catalyst (1.156 A mgPt−1 under similar conditions). It also demonstrates an outstanding mass activity for OER (0.278 A mgCo−1). The Zn‐air battery based on this bifunctional catalyst exhibits high energy density of 945 Wh kgZn−1 as well as remarkable stability. In addition, both density functional theory based simulations and experimental measurements suggest that the CoN4 sites on the carbon matrix are the most active sites for the bifunctional oxygen electrocatalytic activity.
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