Schnapp Esther, Kragl Martin, Rubin Lee, Tanaka Elly M
Max Planck Institute for Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany.
Development. 2005 Jul;132(14):3243-53. doi: 10.1242/dev.01906.
Tail regeneration in urodeles requires the coordinated growth and patterning of the regenerating tissues types, including the spinal cord, cartilage and muscle. The dorsoventral (DV) orientation of the spinal cord at the amputation plane determines the DV patterning of the regenerating spinal cord as well as the patterning of surrounding tissues such as cartilage. We investigated this phenomenon on a molecular level. Both the mature and regenerating axolotl spinal cord express molecular markers of DV progenitor cell domains found during embryonic neural tube development, including Pax6, Pax7 and Msx1. Furthermore, the expression of Sonic hedgehog (Shh) is localized to the ventral floor plate domain in both mature and regenerating spinal cord. Patched1 receptor expression indicated that hedgehog signaling occurs not only within the spinal cord but is also transmitted to the surrounding blastema. Cyclopamine treatment revealed that hedgehog signaling is not only required for DV patterning of the regenerating spinal cord but also had profound effects on the regeneration of surrounding, mesodermal tissues. Proliferation of tail blastema cells was severely impaired, resulting in an overall cessation of tail regeneration, and blastema cells no longer expressed the early cartilage marker Sox9. Spinal cord removal experiments revealed that hedgehog signaling, while required for blastema growth is not sufficient for tail regeneration in the absence of the spinal cord. By contrast to the cyclopamine effect on tail regeneration, cyclopamine-treated regenerating limbs achieve a normal length and contain cartilage. This study represents the first molecular localization of DV patterning information in mature tissue that controls regeneration. Interestingly, although tail regeneration does not occur through the formation of somites, the Shh-dependent pathways that control embryonic somite patterning and proliferation may be utilized within the blastema, albeit with a different topography to mediate growth and patterning of tail tissues during regeneration.
有尾目动物的尾巴再生需要再生组织类型(包括脊髓、软骨和肌肉)的协调生长和模式形成。截肢平面处脊髓的背腹(DV)方向决定了再生脊髓的DV模式以及周围组织(如软骨)的模式。我们在分子水平上研究了这一现象。成熟和再生的美西螈脊髓都表达胚胎神经管发育期间发现的DV祖细胞结构域的分子标记,包括Pax6、Pax7和Msx1。此外,音猬因子(Shh)的表达在成熟和再生脊髓中均定位于腹侧底板结构域。Patched1受体表达表明,刺猬信号不仅在脊髓内发生,还传递到周围的芽基。环杷明处理表明,刺猬信号不仅是再生脊髓DV模式形成所必需的,而且对周围中胚层组织的再生也有深远影响。尾芽基细胞的增殖严重受损,导致尾巴再生完全停止,并且芽基细胞不再表达早期软骨标记物Sox9。脊髓切除实验表明,刺猬信号虽然是芽基生长所必需的,但在没有脊髓的情况下不足以实现尾巴再生。与环杷明对尾巴再生的影响相反,经环杷明处理的再生肢体达到正常长度并含有软骨。这项研究首次在控制再生的成熟组织中对DV模式信息进行了分子定位。有趣的是,尽管尾巴再生不是通过体节的形成发生的,但控制胚胎体节模式形成和增殖的Shh依赖性途径可能在芽基内被利用,尽管其拓扑结构不同,以介导再生过程中尾巴组织的生长和模式形成。