Northcutt R G, Brändle K, Fritzsch B
Scripps Institution of Oceanography, School of Medicine, University of California, San Diego, La Jolla 92093-0201, USA.
Dev Biol. 1995 Apr;168(2):358-73. doi: 10.1006/dbio.1995.1086.
The lateral line system in salamanders consists of mechanoreceptive neuromasts and pit organs, distributed in lines on the head and trunk, and electroreceptive ampullary organs located adjacent to the cephalic lines of mechanoreceptors. Although numerous studies have documented that neuromast and pit organs and the cranial nerves that innervate these receptors arise from a dorsolateral series of placodes, there is no agreement concerning the number of these placodes, the specific groups of receptors that arise from them, or the embryonic origin of ampullary organs. A developmental model was recently proposed (Northcutt et al., 1994) in which all these placodes, except for the most posterior one, elongate to form sensory ridges whose central zones initially form neuromast and pit organ primordia and whose lateral zones subsequently form ampullary primordia. To test this model, individual placodes were unilaterally extirpated, or placodes from pigmented wild-type axolotl embryos were homotopically or heterotopically transplanted into albino hosts. Extirpation resulted in the loss of all three receptor classes, and both homotopic and heterotopic transplants produced pigmented receptors of all three classes in albino hosts. The receptors in the heterotopic transplants still formed lines which occasionally retained their normal orientation despite differentiating in an ectopic environment. These experiments demonstrated that, as previously postulated, specific lines of neuromasts and pit organs do arise from each placode, and ampullary organs also arise from many of the same placodes. The distribution of receptors that develop following incomplete extirpation or heterotopic transplantation also indicates that each placode is patterned regarding receptor classes and orientation prior to sensory ridge formation.
蝾螈的侧线系统由机械感受性神经丘和陷器组成，分布在头部和躯干的线条上，以及位于机械感受器头部线条附近的电感受壶腹器官。尽管许多研究记录了神经丘、陷器以及支配这些感受器的脑神经起源于一系列背外侧基板，但关于这些基板的数量、从中产生的特定感受器群体或壶腹器官的胚胎起源，尚无定论。最近提出了一种发育模型（Northcutt等人，1994年），其中除了最后方的基板外，所有这些基板都会伸长形成感觉嵴，其中心区域最初形成神经丘和陷器原基，其外侧区域随后形成壶腹原基。为了验证该模型，对单个基板进行了单侧切除，或将有色野生型美西螈胚胎的基板同型或异型移植到白化宿主中。切除导致所有三类感受器丧失，同型和异型移植均在白化宿主中产生了所有三类有色感受器。异型移植中的感受器仍形成线条，尽管在异位环境中分化，但偶尔仍保持其正常方向。这些实验表明，如先前假设的那样，特定的神经丘和陷器线条确实起源于每个基板，壶腹器官也起源于许多相同的基板。不完全切除或异型移植后发育的感受器分布也表明，每个基板在感觉嵴形成之前就已根据感受器类别和方向进行了模式化。
