Imokawa Y, Yoshizato K
Yoshizato MorphoMatrix Project, Exploratory Research for Advanced Technology, JST, 5-9-6, Tohkohdai, Tsukuba, Ibaraki 300-26, Japan.
Proc Natl Acad Sci U S A. 1997 Aug 19;94(17):9159-64. doi: 10.1073/pnas.94.17.9159.
This study aimed at characterizing the Sonic hedgehog (shh) gene in newt limbs, which encodes a signaling molecule of the zone of polarizing activity (ZPA) responsible for determining the anterior-posterior axis of the embryonic chicken and mouse limbs. The reverse transcription-PCR showed that adult newt regenerating limbs express shh genes. In situ hybridization experiments demonstrated that shh genes were expressed in mesenchymal cells of the posterior region of both embryonic buds and regenerating blastemas of newt limbs, strongly suggesting the presence of ZPA in these tissues. Experiments of the axial reversal graft of blastemas further supported this suggestion. The grafted blastemas regenerated supernumerary limbs, and this has been explained by three models: the polar coordinate model, the boundary model, and the polarizing zone model. In favor of the third model, the shh gene was expressed not only in the original region (new anterior region) of the graft, but also ectopically in the other region (new posterior region) of the same graft. This study implies that the regenerating limb blastema produces ZPA as the signaling center of the AP patterning as in the developing limb bud and, therefore, supports the notion that the limb regeneration recapitulates the limb development.
本研究旨在对蝾螈肢体中的音猬因子（shh）基因进行特征描述，该基因编码一种极化活性区（ZPA）的信号分子，负责确定胚胎期鸡和小鼠肢体的前后轴。逆转录聚合酶链反应表明，成年蝾螈再生肢体表达shh基因。原位杂交实验证明，shh基因在蝾螈肢体胚胎芽和再生芽基后部区域的间充质细胞中表达，这有力地表明这些组织中存在ZPA。芽基轴向逆转移植实验进一步支持了这一观点。移植的芽基再生出多余的肢体，对此有三种模型进行了解释：极坐标模型、边界模型和极化区模型。支持第三种模型的是，shh基因不仅在移植体的原始区域（新的前部区域）表达，而且在同一移植体的其他区域（新的后部区域）异位表达。本研究表明，再生肢体芽基如同发育中的肢体芽一样，产生ZPA作为前后模式形成的信号中心，因此，支持了肢体再生重现肢体发育这一观点。
