Institute for Structural and Molecular Biology, University College London, London, UK.
J Anat. 2010 Jul;217(1):16-25. doi: 10.1111/j.1469-7580.2010.01239.x. Epub 2010 Apr 26.
Limb regeneration in salamanders proceeds by formation of the blastema, a mound of proliferating mesenchymal cells surrounded by a wound epithelium. Regeneration by the blastema depends on the presence of regenerating nerves and in earlier work it was shown that axons upregulate the expression of newt anterior gradient (nAG) protein first in Schwann cells of the nerve sheath and second in dermal glands underlying the wound epidermis. The expression of nAG protein after plasmid electroporation was shown to rescue a denervated newt blastema and allow regeneration to the digit stage. We have examined the dermal glands by scanning and transmission electron microscopy combined with immunogold labelling of the nAG protein. It is expressed in secretory granules of ductless glands, which apparently discharge by a holocrine mechanism. No external ducts were observed in the wound epithelium of the newt and axolotl. The larval skin of the axolotl has dermal glands but these are absent under the wound epithelium. The nerve sheath was stained post-amputation in innervated but not denervated blastemas with an antibody to axolotl anterior gradient protein. This antibody reacted with axolotl Leydig cells in the wound epithelium and normal epidermis. Staining was markedly decreased in the wound epithelium after denervation but not in the epidermis. Therefore, in both newt and axolotl the regenerating axons induce nAG protein in the nerve sheath and subsequently the protein is expressed by gland cells, under (newt) or within (axolotl) the wound epithelium, which discharge by a holocrine mechanism. These findings serve to unify the nerve dependence of limb regeneration.
蝾螈的肢体再生是通过形成芽基（blastema）来进行的，芽基是一个由增殖的间充质细胞组成的丘状结构，周围环绕着伤口上皮。芽基的再生依赖于再生神经的存在，在早期的工作中已经表明，轴突首先在上皮神经鞘的施万细胞中上调新蝾螈前梯度（nAG）蛋白的表达，其次在伤口上皮下的真皮腺中上调其表达。质粒电穿孔后的 nAG 蛋白表达被证明可以挽救去神经的蝾螈芽基，并允许其再生到指节阶段。我们通过扫描和透射电子显微镜结合 nAG 蛋白的免疫金标记检查了真皮腺。它在无管腺的分泌颗粒中表达，这些腺显然通过全质分泌机制释放分泌物。在新蝾螈和蝾螈的伤口上皮中没有观察到外部导管。蝾螈幼虫的皮肤有真皮腺，但在伤口上皮下没有。在有神经支配的芽基中，神经鞘在截肢后被染色，而在去神经支配的芽基中则不染色，用抗蝾螈前梯度蛋白的抗体进行染色。该抗体在伤口上皮中的蝾螈莱迪希细胞和正常表皮中反应。去神经支配后，伤口上皮中的染色明显减少，但表皮中没有。因此，在新蝾螈和蝾螈中，再生轴突在上皮神经鞘中诱导 nAG 蛋白的表达，随后该蛋白由腺细胞表达，在（新蝾螈）或在（蝾螈）伤口上皮下，通过全质分泌机制释放分泌物。这些发现有助于统一肢体再生的神经依赖性。
