Kitzmann Magali, Bonnieu Anne, Duret Cédric, Vernus Barbara, Barro Marietta, Laoudj-Chenivesse Dalila, Verdi Joseph M, Carnac Gilles
Adult stem cells and facioscapulohumeral dystrophy," CNRS FRE2593, 1919 route de Mende, 34293 Montpellier 5, France.
J Cell Physiol. 2006 Sep;208(3):538-48. doi: 10.1002/jcp.20688.
During muscle differentiation, a population of quiescent undifferentiated myoblasts (reserve cells) emerges among mature muscle cells. However, the molecular mechanisms underlying such cell segregation and the characterization of this subpopulation of myoblasts remain to be determined. Notch is known to control the behavior and fate of murine muscle stem cells. In this study, we examined the role of Notch in myoblast segregation. We showed that inhibition of Notch activity by either overexpressing Numb or by using a pharmacological gamma-secretase inhibitor (DAPT) enhanced differentiation of murine and human myoblasts. This effect was not restricted to in vitro culture systems since DAPT-treated zebrafish embryos also showed increased differentiation. Using C2.7 myoblasts as a model, we showed that inhibition of Notch induced myotube hypertrophy by recruiting reserve cells that do not normally fuse. We further showed that endogenous Notch-signaling components were differentially expressed and activated in reserve cells with respect to Notch 1 and CD34 expression. We identified CD34 negative reserve cells as the subpopulation of myoblasts recruited to fuse into myotubes during differentiation in response to Notch inhibition. Therefore, we showed here that the activation of Notch 1 is important to maintain a subpopulation of CD34 negative reserve cells in an undifferentiated state.
在肌肉分化过程中，一群静止的未分化成肌细胞（储备细胞）出现在成熟肌细胞之中。然而，这种细胞分离背后的分子机制以及该亚群成肌细胞的特征仍有待确定。已知Notch可控制小鼠肌肉干细胞的行为和命运。在本研究中，我们研究了Notch在成肌细胞分离中的作用。我们发现，通过过表达Numb或使用药理学γ-分泌酶抑制剂（DAPT）抑制Notch活性，可增强小鼠和人类成肌细胞的分化。这种效应并不局限于体外培养系统，因为经DAPT处理的斑马鱼胚胎也表现出分化增加。以C2.7成肌细胞为模型，我们发现抑制Notch可通过募集通常不融合的储备细胞诱导肌管肥大。我们进一步表明，内源性Notch信号成分在储备细胞中相对于Notch 1和CD34的表达存在差异表达和激活。我们将CD34阴性储备细胞鉴定为在分化过程中响应Notch抑制而被募集融合到肌管中的成肌细胞亚群。因此，我们在此表明，Notch 1的激活对于维持CD34阴性储备细胞亚群处于未分化状态很重要。
