Role of Retinoic acid in Limb Regeneration

两栖动物肢体再生芽基已被广泛用于分析肢体再生能力和再生模式的形成。无尾两栖类是一种有趣的材料，因为在变态过程中再生能力逐渐下降。视黄酸被认为是调节有尾目两栖类的肢体模式。将断肢后的动物饲养在含维甲酸的水中，诱导了近远侧重复肢、前半胚基完全肢形成和背半胚基完全肢形成，这是由于位置值从远侧到近侧的变化引起的，本研究的目的是观察视黄酸对大鼠胚胎发育肢芽基的影响。Stocum教授发现了无尾两栖类的肢芽基位置值的变化，其结果如下：1.在非洲爪蟾中检测到了shh表达，作为位置值后验化的分子标记，shh在肢芽和芽基的后缘表达，这是shh在芽基中表达的第一个证据。2.视黄酸抑制肢的发育和再生，但位置值的变化是否发生仍不确定。3.通过将分离的肢芽间充质组成的重组肢芽移植，结果表明，在胚胎发育过程中，由于胚基中不同位置间质的分选和调控功能的丧失，导致了30-50指的足的形成，视黄酸对足多指形成的影响正在研究中

Regeneration blastema of amphibian limbs has been widely used for the analysis of regeneration potency and pattern formation. Anuran amphibians were regarded as an interesting material for such analysis since the regeneration potency gradually decreased during the course of metamorphosis.Retinoic acid is known to modulate limb pattern in urodela amphibians. By rearing the animal in retinoic acid-contaning water after limb amputation, the proximo-distal duplication of limbs, complete limb formation from anterior half blastema and complete limb formationfrom dorsal half blastema have been induced which were caused by the changes in positional values from distal to proximal, from anterior to posterior and from dorsal to ventral.The aim of this project is to examine the effects of retinoic acid administration on the rehenerating limb blastema of anuran amphibians by collaborting with Prof.Stocum who found the changes in positional values in urodela limb blastema.The results obtained were as fllows :1.As a molecular marker for the posteriorization of positional value, sonic hedgehog expression (shh) was examined in Xenopus.shh was expressed in the posterior margin of limb bud and blastema, which was the first evidence on shh expression in the blastema.2.Retinoic acid inhibited the limb development and regeneration.It remains uncertain whether the chages in positional value occur or not.3.By grafting recombinant limb bud composed of dissociated limb bud mesenchyme, feet with 30-50 digits were formed, which may be induced by the sorting out of the mesenchyme with different positional values and loss of regulation potency in the blastema.The study on the effects of retinoic acid on this multiple digit formation is now in progress