Thaller C, Eichele G
Nature. 1987;327(6123):625-8. doi: 10.1038/327625a0.
All-trans-retinoic acid (RA) induces striking digit pattern duplications when locally applied to the developing chick limb bud. Instead of the normal digit pattern (234) a mirror-symmetrical 432234 pattern can be specified. Hence, RA closely mimics posterior limb bud tissue (the zone of polarizing activity, ZPA) that causes very similar duplications when grafted to an anterior site of a host limb bud. This resemblance raises an intriguing possibility: that RA is related to the as yet unidentified inducer substance thought to be released by the ZPA. Here we report that chick limb buds contain endogenous RA and we show that RA, but not its biosynthetic precursor retinol, forms a concentration gradient across the limb anlage with a high-point in the posterior domain of the limb bud, the part that also contains the ZPA.
全反式维甲酸（RA）局部应用于发育中的鸡胚肢芽时，会诱导出明显的指型重复现象。正常的指型为（234），而此时可形成镜像对称的432234指型。因此，RA与后肢芽组织（极化活性区，ZPA）极为相似，将ZPA移植到宿主肢芽的前部时也会引起非常相似的重复现象。这种相似性引发了一个有趣的可能性：RA与一种尚未确定的诱导物质有关，这种诱导物质被认为是由ZPA释放的。在此我们报告，鸡胚肢芽中含有内源性RA，并且我们发现RA而非其生物合成前体视黄醇，在肢体原基上形成了一个浓度梯度，在肢芽的后区域浓度最高，该区域也包含ZPA。
