Effects of retinoic acid on limb bud pattern formation and limb blastema pattern formation

为探讨维甲酸（RA）在发育中的肢芽和再生的肢胚中诱导模式形成的共同机制，本研究采用RA处理20期鸡肢芽10 h后，在18-19期将RA头附近的间充质组织移植到其他肢芽的前缘。经ra处理和移植的组织形成了从肱骨到趾的所有软骨元素，而对照移植的组织根据其命运只形成了指。这种“近端化”独立于后端化发生，即诱导ZPA。在正常肢体发育中，HoxA的表达模式会随着近端位置值的变化而变化，而在ra处理的移植中，HoxA的表达模式则改变为近端位置值。单元格亲和度也会根据位置值发生变化。在单层培养中，经ra处理的间充质解离细胞与未处理的间充质解离细胞表现出接近分离的趋势。这些结果表明，ra处理后的发育肢间质细胞的位置值发生了变化，呈现近端化，而不是像之前在蝾螈肢体再生胚中所显示的那样呈现后端化。

To examine common mechanisms of Retinoic acid (RA)-induced pattern formation in the developing limb bud and regenerating limb blastema, chick limb bud at satge 20 was treated with RA for 10 hours by implanting RA-bead and then the mesenchymal tissue near the bead was transplanted to the anterior margin of otherlimb bud at stage 18-19. The RA-treated and transplanted tissues formed all the cartilage elements from humerus to degits, although the control transplants formed only digits according to their fate. This "proximalization" occurred independently of posteriorization, that is, induction of ZPA.The expression pattern of HoxA, which was known to change corresponding to the proximodistal positional value in normal limb development, changed to show the proximalization in RA-treated transplants. The cell affinity also changes according to the positional values. The dissociated cells of RA-treated mesenchyme showed the proximalization to segregate from those of untreated tissues in monolayr culture. These results suggest that the cells of RA-treated mesenchyme of developing limb changes their positional value to show proximalization other than posteriorization as shown previously in regeneration blastema of salamander limb.