Evidence that mechanisms of fin development evolved in the midline of early vertebrates
Evidence that mechanisms of fin development evolved in the midline of early vertebrates
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DOI：
10.1038/nature04984
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发表时间：
2006-08-31
期刊：
影响因子：
64.8
通讯作者：
Cohn, Martin J.
中科院分区：
文献类型：
--
作者：
Freitas, Renata;Zhang, GuangJun;Cohn, Martin J.
成对附肢的起源是脊椎动物进化的一个重大创新，标志着鳍（以及后来的肢体）驱动运动的第一步。最早的脊椎动物化石没有成对的鳍，但有发达的中鳍（1，2），这表明鳍发育的机制首先在中线组装。在这里，我们表明，鲨鱼中鳍的发展涉及相同的遗传程序，在成对的附属物。使用不同细胞类型的分子标记，我们发现，中鳍主要来自体节（近轴）中胚层，而成对的附属物从侧板中胚层发展。Hoxd和Tbx 18基因的表达，指定了成对的肢体位置（3，4），也描绘了中鳍的位置。中鳍的近中端发育发生在顶端外胚层脊下，该结构控制成对附属物的生长（5-7）。然后，每个中鳍芽获得一种前后嵌套的Hoxd表达模式，类似于在四肢中建立骨骼极性的模式（8，9）。因此，尽管它们的胚胎起源不同，但成对鳍和中鳍利用一套共同的发育机制。我们将我们的分析扩展到七鳃鳗，在成对附属物起源之前，它们从导致有颌动物的谱系中分化出来（2，10），并表明它们的中鳍也从体节发育而来，并表达正向Hox和Tbx基因。总之，这些结果表明，鳍发育的分子机制起源于早期脊椎动物的体节中胚层，成对的附属物的起源与重新部署这些机制侧板中胚层。
The origin of paired appendages was a major evolutionary innovation for vertebrates, marking the first step towards fin( and later limb-) driven locomotion. The earliest vertebrate fossils lack paired fins but have well-developed median fins(1,2), suggesting that the mechanisms of fin development were assembled first in the midline. Here we show that shark median fin development involves the same genetic programs that operate in paired appendages. Using molecular markers for different cell types, we show that median fins arise predominantly from somitic ( paraxial) mesoderm, whereas paired appendages develop from lateral plate mesoderm. Expression of Hoxd and Tbx18 genes, which specify paired limb positions(3,4), also delineates the positions of median fins. Proximodistal development of median fins occurs beneath an apical ectodermal ridge, the structure that controls outgrowth of paired appendages(5-7). Each median fin bud then acquires an anteroposteriorly-nested pattern of Hoxd expression similar to that which establishes skeletal polarity in limbs(8,9). Thus, despite their different embryonic origins, paired and median fins utilize a common suite of developmental mechanisms. We extended our analysis to lampreys, which diverged from the lineage leading to gnathostomes before the origin of paired appendages(2,10), and show that their median fins also develop from somites and express orthologous Hox and Tbx genes. Together these results suggest that the molecular mechanisms for fin development originated in somitic mesoderm of early vertebrates, and that the origin of paired appendages was associated with re-deployment of these mechanisms to lateral plate mesoderm.