Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK.
Development. 2011 Sep;138(17):3745-57. doi: 10.1242/dev.070318. Epub 2011 Jul 27.
The midbrain-hindbrain interface gives rise to a boundary of particular importance in CNS development as it forms a local signalling centre, the proper functioning of which is essential for the formation of tectum and cerebellum. Positioning of the mid-hindbrain boundary (MHB) within the neuroepithelium is dependent on the interface of Otx2 and Gbx2 expression domains, yet in the absence of either or both of these genes, organiser genes are still expressed, suggesting that other, as yet unknown mechanisms are also involved in MHB establishment. Here, we present evidence for a role for Notch signalling in stabilising cell lineage restriction and regulating organiser gene expression at the MHB. Experimental interference with Notch signalling in the chick embryo disrupts MHB formation, including downregulation of the organiser signal Fgf8. Ectopic activation of Notch signalling in cells of the anterior hindbrain results in an exclusion of those cells from rhombomeres 1 and 2, and in a simultaneous clustering along the anterior and posterior boundaries of this area, suggesting that Notch signalling influences cell sorting. These cells ectopically express the boundary marker Fgf3. In agreement with a role for Notch signalling in cell sorting, anterior hindbrain cells with activated Notch signalling segregate from normal cells in an aggregation assay. Finally, misexpression of the Notch modulator Lfng or the Notch ligand Ser1 across the MHB leads to a shift in boundary position and loss of restriction of Fgf8 to the MHB. We propose that differential Notch signalling stabilises the MHB through regulating cell sorting and specifying boundary cell fate.
中脑-后脑界面在中枢神经系统发育中形成了一个特别重要的边界，它形成了一个局部信号中心，其正常功能对于脑桥和小脑的形成是必不可少的。中后脑边界（MHB）在神经上皮内的定位取决于 Otx2 和 Gbx2 表达域的界面，但在缺乏这些基因中的任一个或两个基因的情况下，组织者基因仍然表达，这表明其他尚未知的机制也参与了 MHB 的建立。在这里，我们提供了证据表明 Notch 信号在稳定细胞谱系限制和调节 MHB 处的组织者基因表达方面具有作用。在鸡胚中实验性干扰 Notch 信号会破坏 MHB 的形成，包括下调组织者信号 Fgf8。在前后后脑细胞中异位激活 Notch 信号会导致这些细胞从 rhombomeres 1 和 2 中排除，并同时沿着该区域的前后边界聚集，这表明 Notch 信号影响细胞分选。这些细胞异位表达边界标记物 Fgf3。与 Notch 信号在细胞分选中的作用一致，具有激活 Notch 信号的前后脑细胞在聚集测定中与正常细胞分离。最后，在 MHB 上异位表达 Notch 调节剂 Lfng 或 Notch 配体 Ser1 会导致边界位置发生变化，并且 Fgf8 对 MHB 的限制丧失。我们提出，差异 Notch 信号通过调节细胞分选和指定边界细胞命运来稳定 MHB。
