Saga Yumiko
Division of Mammalian Development, National Institute of Genetics, and Department of Genetics, Sokendai, Mishima, Japan.
Dev Dyn. 2007 Jun;236(6):1450-5. doi: 10.1002/dvdy.21143.
Elaborate somite patterning is based upon dynamic gene regulation within the presomitic mesoderm (PSM), which is derived from the primitive streak and tail bud in the later stage mouse embryo. The Notch signaling pathway and its regulators are major components of most of the events required for temporally and spatially coordinated somite formation. The PSM can be subdivided into at least two domains, based upon transcriptional regulation and gene function. In the posterior PSM, the basic helix-loop-helix (bHLH) protein Hes7 plays a central role in generating a traveling wave of gene expression by negatively regulating the transcription of its target genes. This in turn may define the somite spacing and future segmental units. In the anterior PSM, cells begin to form segmental patterning by acquiring rostral or caudal identities of somite primordia and by defining the segmental border, which must be coupled with the segmentation clock. The link between the clock and segmental border formation is of fundamental importance during somitogenesis. During this process, Mesp2, another basic HLH protein, plays a critical role in the anterior PSM. In this review, I further clarify the dynamic processes leading to segmental border formation in the developing mouse embryo.
精细的体节模式形成基于前体中胚层（PSM）内的动态基因调控，前体中胚层源自晚期小鼠胚胎的原条和尾芽。Notch信号通路及其调节因子是时空协调体节形成所需的大多数事件的主要组成部分。基于转录调控和基因功能，PSM可至少分为两个区域。在后部PSM中，碱性螺旋-环-螺旋（bHLH）蛋白Hes7通过负调控其靶基因的转录，在产生基因表达的行波中发挥核心作用。这反过来可能决定体节间距和未来的节段单位。在前部PSM中，细胞通过获得体节原基的头侧或尾侧身份并确定节段边界开始形成节段模式，节段边界必须与分割时钟相耦合。在体节发生过程中，时钟与节段边界形成之间的联系至关重要。在此过程中，另一种碱性HLH蛋白Mesp2在前部PSM中起关键作用。在这篇综述中，我进一步阐明了发育中的小鼠胚胎中导致节段边界形成的动态过程。
