Evolution of the somatotopic map in the vertebrate hindbrain

为了明确脊椎动物三叉神经系统中躯体位置组织的进化过程，我们比较了发育中的龟、鸡和小鼠的三叉神经组织。我们发现，虽然下颌骨和上颌分支的躯体形态是保守的乌龟，这些分支在小鸡没有严格的空间隔离，和它们的位置在三叉神经束是颠倒的，相比，小鼠。此外，通过使用这种特异性标记物与Hoxa 2和来自外周的轴突示踪相结合，我们绘制了鸡PrV在菱形节（r）1中的位置，而不像小鼠PrV主要在r2-r3中绘制。因此，三叉神经节和神经组织的躯体解剖学仅部分地通过神经元进化而被保存，这可能与面部躯体感觉结构和形态的改变有关。

To identify the evolutionary process of somatotopic organization in vertebrate trigeminal system, we compared trigeminal nerve organization in developing turtle, chick, and mouse. We found that, while mandibular and maxillary branch somatotopy is conserved in turtle, these branches in the chick are not strictly spatially segregated, and their position in the trigeminal tract is inversed, as compared to mouse. Furthermore, by using this specific marker in combination with Hoxa2 and axonal tracings from the periphery, we mapped the position of chick PrV in rhombomere(r) 1, unlike mouse PrV that mainly maps in r2-r3. Thus, somatotopy of trigeminal ganglion and nerve organization is only partially conserved through amniote evolution, possibly in relation to the modification of facial somatosensory structures and morphologies.