Dept of Molecular and Cell Biology and Center for Integrative Genomics, University of California, Berkeley, CA 94720, USA.
Dev Biol. 2011 Apr 15;352(2):254-66. doi: 10.1016/j.ydbio.2011.01.021. Epub 2011 Jan 27.
The development of the vertebrate dorsal midline (floor plate, notochord, and hypochord) has been an area of classical research and debate. Previous studies in vertebrates have led to contrasting models for the roles of Shh and Notch signaling in specification of the floor plate, by late inductive or early allocation mechanisms, respectively. Here, we show that Notch signaling plays an integral role in cell fate decisions in the dorsal midline of Xenopus laevis, similar to that observed in zebrafish and chick. Notch signaling promotes floor plate and hypochord fates over notochord, but has variable effects on Shh expression in the midline. In contrast to previous reports in frog, we find that Shh signaling is not required for floor plate vs. notochord decisions and plays a minor role in floor plate specification, where it acts in parallel to Notch signaling. As in zebrafish, Shh signaling is required for specification of the lateral floor plate in the frog. We also find that the medial floor plate in Xenopus comprises two distinct populations of cells, each dependent upon different signals for its specification. Using expression analysis of several midline markers, and dissection of functional relationships, we propose a revised allocation mechanism of dorsal midline specification in Xenopus. Our model is distinct from those proposed to date, and may serve as a guide for future studies in frog and other vertebrate organisms.
脊椎动物背中线（基板、脊索和脊索下组织）的发育一直是经典研究和争论的领域。脊椎动物的先前研究导致了 Shh 和 Notch 信号在基板特化中的作用的对比模型，分别通过晚期诱导或早期分配机制。在这里，我们表明 Notch 信号在非洲爪蟾的背中线细胞命运决定中起着不可或缺的作用，这与在斑马鱼和鸡中观察到的作用相似。Notch 信号促进基板和脊索下组织的命运，而不是脊索，但对中线 Shh 表达有不同的影响。与在青蛙中的先前报告相反，我们发现 Shh 信号不是基板与脊索决定所必需的，并且在基板特化中起次要作用，其中它与 Notch 信号平行作用。与在斑马鱼中一样，Shh 信号是青蛙中侧向基板特化所必需的。我们还发现，非洲爪蟾的基板内侧由两个不同的细胞群组成，每个细胞群的特化都依赖于不同的信号。通过对几个中线标记物的表达分析，以及对功能关系的剖析，我们提出了非洲爪蟾背中线特化的一种新的分配机制。我们的模型与迄今为止提出的模型不同，它可能为青蛙和其他脊椎动物的未来研究提供指导。
