Pourquie O
Developmental Biology Institute of Marseille, Université de la Méditerranée, France.
J Anat. 2001 Jul-Aug;199(Pt 1-2):169-75. doi: 10.1046/j.1469-7580.2001.19910169.x.
Vertebrate somitogenesis has been shown to be associated with a molecular oscillator, the segmentation clock, whose periodicity matches that of the process of somitogenesis. The existence of such a clock in presomitic mesoderm (PSM) cells was originally proposed in theoretical models such as the 'clock and wavefront'. Molecular evidence for the existence of this clock in vertebrates has been obtained on the basis of the periodic expression of several genes, most of which are related to the Notch signalling pathway. These genes are expressed in a dynamic sequence which appears as a wave sweeping caudo-rostrally along the whole PSM once during each somite formation. Notch-pathway mouse and fish mutants lose the dynamic expression of the cycling genes, indicating that Notch signalling is required for their periodic expression, or is required to coordinate the oscillations between PSM cells. Therefore Notch signalling is either part of the mechanism of the oscillator itself or acts as a cofactor required for cycling gene expression. A further potentially important role for the segmentation clock is to periodically activate Notch signalling in the rostral presomitic mesoderm, thereby generating the periodic formation of somite boundaries.
脊椎动物的体节发生已被证明与一种分子振荡器——体节时钟相关，其周期性与体节发生过程的周期性相匹配。这种时钟在原肠胚中胚层（PSM）细胞中的存在最初是在“时钟和波阵面”等理论模型中提出的。基于几个基因的周期性表达，已经获得了脊椎动物中这种时钟存在的分子证据，其中大多数基因与Notch信号通路有关。这些基因以动态序列表达，在每个体节形成过程中，这种序列会像波浪一样沿整个PSM从尾端向头端扫过一次。Notch信号通路的小鼠和鱼类突变体失去了循环基因的动态表达，这表明Notch信号对于它们的周期性表达是必需的，或者是协调PSM细胞之间振荡所必需的。因此，Notch信号要么是振荡器本身机制的一部分，要么作为循环基因表达所需的辅助因子发挥作用。体节时钟的另一个潜在重要作用是在头端原肠胚中胚层中周期性地激活Notch信号，从而产生体节边界的周期性形成。
