Sylvius Laboratory, Leiden, The Netherlands.
Genomics. 2010 May;95(5):250-5. doi: 10.1016/j.ygeno.2009.11.002. Epub 2009 Nov 26.
Here, we review a recently discovered developmental mechanism. Anterior-posterior positional information for the vertebrate trunk is generated by sequential interactions between a timer in the early non-organiser mesoderm and the Spemann organiser. The timer is characterised by temporally colinear activation of a series of Hox genes in the early ventral and lateral mesoderm (i.e., the non-organiser mesoderm) of the Xenopus gastrula. This early Hox gene expression is transient, unless it is stabilised by signals from the Spemann organiser. The non-organiser mesoderm (NOM) and the Spemann organiser undergo timed interactions during gastrulation which lead to the formation of an anterior-posterior axis and stable Hox gene expression. When separated from each other, neither non-organiser mesoderm nor the Spemann organiser is able to induce anterior-posterior pattern formation of the trunk. We present a model describing that NOM acquires transiently stable hox codes and spatial colinearity after involution into the gastrula and that convergence and extension then continually bring new cells from the NOM within the range of organiser signals that cause transfer of the mesodermal pattern to a stable pattern in neurectoderm and thereby create patterned axial structures. In doing so, the age of the non-organiser mesoderm, but not the age of the organiser, defines positional values along the anterior-posterior axis. We postulate that the temporal information from the non-organiser mesoderm is linked to mesodermal Hox expression. The role of the organiser was investigated further and this turns out to be only the induction of neural tissue. Apparently, development of a stable axial hox pattern requires neural hox patterning.
在这里，我们回顾了一个最近发现的发育机制。脊椎动物躯干的前后位置信息是由早期非组织者中胚层的计时器与 Spemann 组织者之间的顺序相互作用产生的。该计时器的特征是在 Xenopus 原肠胚的早期腹侧和侧中胚层（即非组织者中胚层）中一系列 Hox 基因的时间上线性激活（即非组织者中胚层）。这种早期 Hox 基因表达是短暂的，除非它受到 Spemann 组织者信号的稳定。非组织者中胚层（NOM）和 Spemann 组织者在原肠胚形成过程中进行定时相互作用，导致前后轴的形成和稳定的 Hox 基因表达。当彼此分离时，非组织者中胚层或 Spemann 组织者都不能诱导躯干的前后模式形成。我们提出了一个模型，描述了 NOM 在卷入原肠胚后获得暂时稳定的 hox 编码和空间共线性，然后收敛和延伸不断将来自 NOM 的新细胞带入组织者信号范围内，导致中胚层模式转移到神经外胚层中的稳定模式，从而创建有图案的轴向结构。这样，非组织者中胚层的年龄而不是组织者的年龄定义了沿前后轴的位置值。我们假设非组织者中胚层的时间信息与中胚层 Hox 表达有关。进一步研究了组织者的作用，结果表明它只是神经组织的诱导。显然，稳定的轴向 hox 模式的发展需要神经 hox 模式化。
