这里,我们回顾了最近发现的发育机制。脊椎动物躯干的前后位置信息是通过早期非组织者中胚层中的计时器与Spemann组织者之间的顺序相互作用生成的。计时器的特征在于早期腹侧和外侧中胚层中一系列Hox基因的时序共线激活(即,非洲爪狼的非组织者中胚层)。这种早期的Hox基因表达是短暂的,除非它被Spemann组织者的信号稳定。非组织者中胚层(NOM)和Spemann组织者在原肠胚形成过程中会发生定时相互作用,从而导致前后轴的形成和稳定的Hox基因表达。当彼此分开时,非组织者中胚层和Spemann组织者都不能诱导躯干的前后模式形成。我们提供了一个模型,该模型描述了NOM在对合到胃中后获得了暂时稳定的hox代码和空间共线性,并且收敛和扩展然后不断地从NOM带来新的细胞,这些细胞处于组织者信号的范围内,从而导致中胚层模式转移到稳定的模式。在这样做的时候,非组织者中胚层的年龄,但不是组织者的年龄,定义沿前后轴的位置值。我们假设来自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,事实证明这仅是神经组织的诱导。显然,稳定的轴向hox模式的发展需要神经hox模式。
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.