Wanek N, Gardiner D M, Muneoka K, Bryant S V
Developmental Biology Center, University of California, Irvine 92717.
Nature. 1991 Mar 7;350(6313):81-3. doi: 10.1038/350081a0.
In recent years there has been considerable interest in the role of retinoic acid (RA) in vertebrate-limb pattern formation. When RA is applied to the anterior of the chick wing bud, a mirror-image duplication of the limb pattern develops that is identical to the pattern resulting from grafts of posterior tissue (zone of polarizing activity, or ZPA). It has been proposed that position along the anterior-posterior axis in the chick limb is specified by a gradient of a diffusible factor produced by the ZPA. The ZPA-mimicking action of RA has led to the hypothesis that exogenously applied RA acts by providing graded spatial information across the anterior-posterior limb axis. An alternative interpretation is that RA changes anterior cells into ZPA cells, which in turn provide the actual pattern-duplicating stimulus; there is already some preliminary evidence that this occurs. A hybrid interpretation has also been suggested whereby ZPA cells are formed in response to RA exposure and then begin to release retinoids that act as graded spatial cues. We have used a functional assay to test anterior chick wing-bud cells for ZPA activity after exposure to RA. The results of our studies indicate that the action of RA is to change anterior cells into ZPA cells. Further, our results indicate that it is unlikely that RA-treated anterior cells then begin producing RA in such a way as to provide a graded positional signal.
近年来，视黄酸（RA）在脊椎动物肢体模式形成中的作用引起了广泛关注。当将RA应用于鸡胚翼芽的前部时，会形成肢体模式的镜像重复，这与后部组织移植（极化活性区，或ZPA）所产生的模式相同。有人提出，鸡胚肢体中沿前后轴的位置是由ZPA产生的一种可扩散因子的梯度所确定的。RA的ZPA模拟作用导致了这样一种假说，即外源性应用的RA通过在前后肢体轴上提供分级空间信息来发挥作用。另一种解释是，RA将前部细胞转变为ZPA细胞，而ZPA细胞反过来提供实际的模式复制刺激；已经有一些初步证据表明这种情况会发生。也有人提出了一种混合解释，即ZPA细胞是在暴露于RA后形成的，然后开始释放作为分级空间线索的类视黄醇。我们使用了一种功能测定法来测试暴露于RA后的鸡胚翼芽前部细胞的ZPA活性。我们的研究结果表明，RA的作用是将前部细胞转变为ZPA细胞。此外，我们的结果表明，经RA处理的前部细胞不太可能随后开始以提供分级位置信号的方式产生RA。
