Cordes Ralf, Schuster-Gossler Karin, Serth Katrin, Gossler Achim
Institut für Molekularbiologie OE5250, Medizinische Hochschule, Carl-Neuberg-Str. 1, D-30625 Hannover, Germany.
Development. 2004 Mar;131(6):1221-33. doi: 10.1242/dev.01030. Epub 2004 Feb 11.
To further analyse requirements for Notch signalling in patterning the paraxial mesoderm, we generated transgenic mice that express in the paraxial mesoderm a dominant-negative version of Delta1. Transgenic mice with reduced Notch activity in the presomitic mesoderm as indicated by loss of Hes5 expression were viable and displayed defects in somites and vertebrae consistent with known roles of Notch signalling in somite compartmentalisation. In addition, these mice showed with variable expressivity and penetrance alterations of vertebral identities resembling homeotic transformations, and subtle changes of Hox gene expression in day 12.5 embryos. Mice that carried only one functional copy of the endogenous Delta1 gene also showed changes of vertebral identities in the lower cervical region, suggesting a previously unnoticed haploinsufficiency for Delta1. Likewise, in mice carrying a null allele of the oscillating Lfng gene, or in transgenic mice expressing Lfng constitutively in the presomitic mesoderm, vertebral identities were changed and numbers of segments in the cervical and thoracic regions were reduced, suggesting anterior shifts of axial identity. Together, these results provide genetic evidence that precisely regulated levels of Notch activity as well as cyclic Lfng activity are critical for positional specification of the anteroposterior body axis in the paraxial mesoderm.
为了进一步分析Notch信号通路在近轴中胚层模式形成中的需求，我们构建了在近轴中胚层表达Delta1显性负性形式的转基因小鼠。如Hes5表达缺失所示，在体节发生前的中胚层中Notch活性降低的转基因小鼠是存活的，并且在体节和椎骨中表现出缺陷，这与Notch信号通路在体节分隔中的已知作用一致。此外，这些小鼠表现出具有可变表达率和外显率的椎体身份改变，类似于同源异型转化，并且在12.5天胚胎中Hox基因表达发生细微变化。仅携带一个内源性Delta1基因功能拷贝的小鼠在颈下部区域也表现出椎体身份的改变，这表明Delta1存在以前未被注意到的单倍剂量不足。同样地，在携带振荡的Lfng基因无效等位基因的小鼠中，或在体节发生前的中胚层中组成型表达Lfng的转基因小鼠中，椎体身份发生改变，颈段和胸段的节段数量减少，表明轴向身份向前移位。总之，这些结果提供了遗传学证据，即精确调控的Notch活性水平以及周期性的Lfng活性对于近轴中胚层前后体轴的位置指定至关重要。
