Tamura K, Yokouchi Y, Kuroiwa A, Ide H
Graduate School of Science, Tohoku University, Aramaki Aobaku, Sendai, 980-77, Japan.
Dev Biol. 1997 Aug 15;188(2):224-34. doi: 10.1006/dbio.1997.8627.
In the developing chick limb bud, retinoic acid (RA) has a striking effect on anteroposterior axis formation, resulting in a duplicated pattern of digits. There is no evidence, however, that RA affects proximodistal axis formation in the developing chick limb bud, although RA induces proximodistal duplication in regenerating amphibian limbs. We describe a series of investigations on the effect of RA on the proximodistal axis in the chick limb bud. A RA-containing bead applied to the anterior margin of the chick limb bud at stage 20 induces the anteroposterior duplication of autopodial structures at the wrist level. We found that the RA-treated tissue has the ability to form more proximal structures. When a tissue graft from the RA-treated anterior region was implanted into a stage 17 wing bud (in which the stylopod is developing in the progress zone), the graft produced a humerus, radius-ulna, and digits. When the graft was implanted into a stage 19 wing bud (in which the zeugopod is developing in the progress zone), a zeugopod and digits were formed. These results were associated with changes in the expression of Hox-A genes in the RA-treated grafts, whose domains were reorganized to be similar to those in host tissues 24 h after grafting. When a small graft of RA-treated tissue was implanted into the apex of a stage 19 wing bud, the cells were found in the zeugopod and autopod, whereas cells of control fragments were found only in the autopod region. In vitro, distal cells from different stage limb buds are known to segregate from each other. However, RA-treated stage 24 distal cells did not sort out from stage 20 distal cells and mixed homogeneously. These results suggest that RA induces distal cells to adopt "younger" properties which render them susceptible to forming more proximal patterns under the direction of host signals. The effects of RA on proximodistal patterns in developing chick limb buds appear to differ from its effects on proximodistal patterns in regenerating urodele limbs because RA can induce the proximodistal duplication in situ in the regenerating limbs.
在发育中的鸡胚肢芽中，视黄酸（RA）对前后轴的形成有显著影响，导致指（趾）的重复模式。然而，没有证据表明RA会影响发育中的鸡胚肢芽的近远轴形成，尽管RA会诱导再生的两栖动物肢体出现近远轴重复。我们描述了一系列关于RA对鸡胚肢芽近远轴影响的研究。在第20阶段，将含有RA的珠子应用于鸡胚肢芽的前缘，会诱导腕部水平的自手部结构出现前后重复。我们发现，经RA处理的组织有能力形成更多近端结构。当将来自经RA处理的前部区域的组织移植到第17阶段的翼芽（其中肱骨正在进展区发育）中时，移植组织产生了肱骨、尺桡骨和指（趾）。当将移植组织植入第19阶段的翼芽（其中桡尺骨正在进展区发育）中时，形成了桡尺骨和指（趾）。这些结果与经RA处理的移植组织中Hox - A基因表达的变化有关，其结构域在移植后24小时重新组织，与宿主组织中的相似。当将一小片经RA处理的组织移植到第19阶段翼芽的顶端时，细胞出现在桡尺骨和自手部，而对照片段的细胞仅出现在自手部区域。在体外，已知来自不同阶段肢芽的远端细胞会相互分离。然而，经RA处理的第24阶段远端细胞不会与第20阶段远端细胞分离，而是均匀混合。这些结果表明，RA诱导远端细胞具有“更年轻”的特性，使其在宿主信号的引导下易于形成更多近端模式。RA对发育中的鸡胚肢芽近远轴模式的影响似乎与其对再生有尾目动物肢体近远轴模式的影响不同，因为RA可在再生肢体中原位诱导近远轴重复。
