Evolution of the somatotopic map in the vertebrate hindbrain

为了确定脊椎动物三叉神经系统中体位组织的进化过程，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，与小鼠相比，乌龟的下颌支和上颌支在体位上是保守的，而雏龟的这些支在空间上并不是严格分离的，而且它们在三叉神经束中的位置是颠倒的。此外，通过使用这个特定的标记结合Hoxa2和来自外围的轴突跟踪，我们定位了鸡PRV在菱形核(R)1中的位置，而不是主要映射在R2-R3中的小鼠PRV。因此，三叉神经节和神经组织的体位在羊膜进化过程中只有部分保守，可能与面部体感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.