Laboratory for Sensory Development, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-Minamimachi, Chuo-ku, Kobe 650-0047, Japan.
Nat Commun. 2012;3:1041. doi: 10.1038/ncomms2036.
The paratympanic organ, a mechanosensory hair cell-containing pouch in the amniote middle ear, was first described 100 years ago, yet its origins remain unresolved. Homology with the anamniote spiracular organ is supported by association with homologous skeletal elements and similar central targets of afferent neurons, suggesting it might be a remnant of the water-dependent lateral line system, otherwise lost during the amniote transition to terrestrial life. However, this is incompatible with studies suggesting that it arises from the first epibranchial (geniculate) placode. Here we show that a previously undiscovered Sox2-positive placode, immediately dorsal to the geniculate placode, forms the paratympanic organ and its afferent neurons, which are molecularly and morphologically distinct from geniculate neurons. These data remove the only obstacle to accepting the homology of the paratympanic organ and spiracular organ. We hypothesize that the paratympanic organ/spiracular organ represents an ancient head ectoderm module, developmentally and evolutionarily independent of both lateral line and epibranchial placodes.
中耳的毗邻鼓室器官是一种含有机械感觉毛细胞的囊状结构，100 年前首次被描述，但它的起源仍未解决。与无羊膜动物的呼吸孔器官的同源性得到了与同源骨骼元素和相似的传入神经元中枢靶点的支持，这表明它可能是水依赖的侧线系统的残余物，否则在羊膜动物向陆地生活的过渡过程中丢失。然而，这与表明它起源于第一对鳃弓（神经节）基板的研究不一致。在这里，我们发现一个以前未被发现的 Sox2 阳性基板，位于神经节基板的正上方，形成毗邻鼓室器官及其传入神经元，这些神经元在分子和形态上与神经节神经元不同。这些数据消除了接受毗邻鼓室器官和呼吸孔器官同源性的唯一障碍。我们假设毗邻鼓室器官/呼吸孔器官代表一个古老的头部外胚层模块，在发育和进化上独立于侧线和鳃弓基板。
