Hadzhiev Yavor, Lele Zsolt, Schindler Simone, Wilson Stephen W, Ahlberg Per, Strähle Uwe, Müller Ferenc
Institute of Toxicology and Genetics, Forschungszentrum Karlsruhe, Karlsruhe, Germany.
BMC Dev Biol. 2007 Jun 27;7:75. doi: 10.1186/1471-213X-7-75.
Little is known about the control of the development of vertebrate unpaired appendages such as the caudal fin, one of the key morphological specializations of fishes. Recent analysis of lamprey and dogshark median fins suggests the co-option of some molecular mechanisms between paired and median in Chondrichthyes. However, the extent to which the molecular mechanisms patterning paired and median fins are shared remains unknown.
Here we provide molecular description of the initial ontogeny of the median fins in zebrafish and present several independent lines of evidence that Sonic hedgehog signaling emanating from the embryonic midline is essential for establishment and outgrowth of the caudal fin primordium. However, gene expression analysis shows that the primordium of the adult caudal fin does not harbor a Sonic hedgehog-expressing domain equivalent to the Shh secreting zone of polarizing activity (ZPA) of paired appendages.
Our results suggest that Hedgehog proteins can regulate skeletal appendage outgrowth independent of a ZPA and demonstrates an unexpected mechanism for mediating Shh signals in a median fin primordium. The median fins evolved before paired fins in early craniates, thus the patterning of the median fins may be an ancestral mechanism that controls the outgrowth of skeletogenic appendages in vertebrates.
对于脊椎动物不成对附肢（如尾鳍，鱼类关键的形态特化之一）发育的调控，我们了解甚少。最近对七鳃鳗和姥鲨中鳍的分析表明，软骨鱼类的成对和中鳍之间存在一些分子机制的共同选择。然而，成对和中鳍模式形成的分子机制共享程度仍不清楚。
在此，我们提供了斑马鱼中鳍初始个体发育的分子描述，并提出了几条独立的证据，表明源自胚胎中线的 Sonic hedgehog 信号对于尾鳍原基的建立和生长至关重要。然而，基因表达分析表明，成年尾鳍的原基并不具有与成对附肢极化活性区（ZPA）中分泌 Shh 的区域相当的 Sonic hedgehog 表达域。
我们的结果表明，Hedgehog 蛋白可以独立于 ZPA 调节骨骼附肢的生长，并证明了在中鳍原基中介导 Shh 信号的意外机制。中鳍在早期有头类动物的成对鳍之前就已进化，因此中鳍的模式形成可能是控制脊椎动物骨骼附肢生长的一种祖先机制。
