New molecular concepts on pattern formation in limb morphogenesis.

关于发育中的肢芽的前后轴的形成，一个在肢芽中具有独特表达模式的基因Mario在前后图案化中起着至关重要的作用，并确定了图案化的分子级联的一部分，包括Mario和BMP。此外，通过对HoxD基因的表达分析，非洲爪蛙前肢的数字不是1234，而是2345。关于肢芽中近端-远端轴的形成，详细的命运图显示，未来的自足区和未来的斑足区在早期的肢芽中大部分是重叠的，但随着发育的进行，重叠的部分越来越小。Hoxa13/Hoxall基因表达谱证实了命运图谱的结果。此外，表达分析还表明，远端肢芽中的分子状态正在发生进行性变化。一系列移植实验表明，来自轴结构、体节的一个因素(S)决定了肢体类型的同一性。不同水平的体节移植诱导了Tbx4/5表达的转变，并抑制了后肢芽的生长。研究了shh表达的表观遗传调控，结果表明shh的表达与shh增强子序列的DNA甲基化有很好的相关性(shh表达的组织在增强子区域的DNA甲基化程度较低)，提示shh增强子区的表观遗传控制在shh的表达中起着重要作用。

In terms of the anterior-posterior axis formation in a developing limb bud, a gene, mario, which has unique expression pattern in the limb bud, has a crucial role in the antero-posterior patterning, and a part of the molecular cascade for the patterning, including mario and bmp, was identified. Also, digit number in Xenopus forelimb is identified as not 1234 but 2345 by expression analysis of HoxD genes.In terms of the proximal-distal axis formation in the limb bud, a detailed fate map showed that future autopod region and future zeugopod region is largely overlapped in an early limb bud, but that the overlap is getting smaller as the development proceeds. Hoxa13/Hoxall expression profile confirmed these results from the fate map. Also, the expression analysis revealed that the molecular condition in the distal limb bud is changing progressively.A series of transplantation experiments suggested that a factor(s) from the axial structure, somites determines limb-type identity. Transplantation of different level of somites induced transition of Tbx4/5 expression and inhibited outgrowth of the hindlimb bud. These results suggest that positioning of limb field and its identity are specified not in an autonomous manner in the lateral plate mesoderm but that the tissue-tissue interactions are important.Epigenetic regulation of shh expression was examined, and the results indicated a well correlation between shh expression and DNA methylation of shh enhancer sequence (shh-expressing tissues had low condition of DNA methylation in the enhancer region), suggesting that epigenetic control of shh enhancer region plays a role in shh expression during limb development and regeneration.