Gañan Y, Macias D, Garcia-Martinez V, Hurle J M
Department of Morphological Sciences, University of Extremadura, Badajoz, Spain.
Prog Clin Biol Res. 1993;383A:127-39.
In previous studies we had found that at late stages of development, when the early patterning control mechanism have ceased to act, the chick limb bud is able to form fully differentiated extradigits by subjecting the interdigital spaces to ectoderm removal. In this study we attempted to mimic this phenomenon by using local microinjections of substances which presumably have a biological action on the interdigital mesenchyme. Microinjection of staurosporine results in the formation of fully differentiated extradigits. The action of this drug appears to be due to the induction of chondrogenesis after the inhibition of the protein kinase C. Zinc chloride administration also causes ectopic chondrogenesis but it seems to act by arresting the interdigital cell death program through endonuclease inhibition. A clear differentiation of the zinc-induced cartilages into extradigits was no detected. This can be explained by the accompanying damage caused by zinc in the growing limb mesenchyme as deduced by the high incidence of hypophalangy in the normal digits. Both TGF beta 1 and TGF beta 2 have a weak effect as inducers of interdigital chondrogenesis; presumably they act by inducing chondrogenetic differentiation. Neither FGF nor EGF has any effect when administered by local microinjection. These results show that ectopic interdigital chondrogenesis induced by drug administration results in the differentiation of extradigits. This suggests that once a cartilage is formed in the autopodium it triggers a new signalling stage which leads to the morphogenesis of a digit. This morphogenetic process involves the patterning of skeleton, joints and tendons. In accordance with these observations, it can be proposed that early patterning of the limb results in the establishment of an autopodium with a defined but still plastic skeletal distribution pattern, while morphogenesis of each autopodial element would take place at a second stage by the activation of new signalling processes.
在先前的研究中我们发现，在发育后期，当早期的模式控制机制停止作用时，通过去除鸡胚肢芽的指间组织，鸡胚肢芽能够形成完全分化的额外指。在本研究中，我们试图通过局部显微注射可能对指间间充质有生物学作用的物质来模拟这一现象。显微注射星形孢菌素会导致完全分化的额外指形成。这种药物的作用似乎是由于在抑制蛋白激酶C后诱导软骨形成。施用氯化锌也会导致异位软骨形成，但它似乎是通过抑制核酸内切酶来阻止指间细胞死亡程序而起作用的。未检测到锌诱导的软骨明显分化为额外指。这可以通过正常指中低指骨发生率所推断的锌对生长中的肢体间充质造成的伴随损伤来解释。转化生长因子β1和转化生长因子β2作为指间软骨形成诱导剂的作用较弱；推测它们通过诱导软骨形成分化而起作用。通过局部显微注射施用时，成纤维细胞生长因子（FGF）和表皮生长因子（EGF）均无任何作用。这些结果表明，药物诱导的异位指间软骨形成导致额外指的分化。这表明一旦在 autopodium 中形成软骨，它就会触发一个新的信号传导阶段，从而导致指的形态发生。这个形态发生过程涉及骨骼、关节和肌腱的模式形成。根据这些观察结果，可以提出肢体的早期模式形成导致建立具有确定但仍具可塑性的骨骼分布模式的 autopodium，而每个 autopodial 元素的形态发生将在第二阶段通过激活新的信号传导过程发生。
