The capacity of stem cells to generate successive classes of committed progeny during development has been well-studied in some systems but is largely undefined for many tissues. Now, on , Shahragim Tajbakhsh and co-workers investigate the role of Notch in the temporal specification potential of mouse skeletal muscle stem cells. The researchers show that Notch is active throughout development in the muscle founder stem cell population, and that expression of activated Notch (NICD) is sufficient to autonomously maintain self-renewing muscle stem/progenitor cells throughout embryogenesis, despite the absence of committed progeny, which were previously shown to be required for muscle stem cell maintenance. NICD-expressing replicating embryonic stem/progenitors respond to foetal environmental cues as development proceeds. Furthermore, the researchers report, siRNA-mediated silencing of NICD in this population promotes the temporally appropriate foetal myogenic fate, despite the expression of markers for multiple cell types. Given these results, the researchers propose that Notch signalling both maintains muscle stem cells and allows them to be receptive to specification cues throughout development.
