Understanding metamorphosis of the amphibian olfactory system at the morphological, molecular, and functional level

脊椎动物的嗅觉面临的一个主要挑战是从水生嗅觉到陆生嗅觉的过渡，因为气味类别明显不同。在这方面，两栖动物代表了硬骨鱼和哺乳动物之间的进化转折点。第二，个体发育转变是两栖动物特有的：变态。这一过程从一只水生蝌蚪中产生了一只陆地成年青蛙，并涉及到嗅觉系统的剧烈重建。然而，对嗅觉系统变形过程中的形态、分子和功能变化知之甚少。我们已经描述了非洲爪哇蝌蚪嗅觉系统的几个新特征，这些特征都反映了该物种的进化转换点，其中最主要的是在幼虫MoE中独占表达一大群V2R受体，并与功能性氨基酸反应共存。因此，两栖动物V2R家族分为犁鼻和主嗅觉上皮，这是一个非常不寻常的特征。在这里，我们建议研究变态过程中这一特征的发展，并分析变态过程中两个主要鼻子、主腔和中腔(分别为气鼻和水鼻)的氨基酸气味反应。为了补充这些研究，我们提出了两种独立的方法来去除非洲爪哇V2R受体，测量在非洲爪哇卵母细胞中异源表达的V2R的气味反应，以及在敲除V2R的一个必要的辅助受体后进行体内成像。

A major challenge for the vertebrate sense of smell has been the transition from aquatic to terrestrial olfaction, since odor classes are distinctly different. In this respect amphibians represent an evolutionary transition point between teleost fish and e.g. mammals. A second, ontogenetic transition is specific to amphibians: metamorphosis. This process generates a terrestrial adult frog from an aquatic tadpole, and involves a drastic reconstruction of the olfactory system. However, very little is known about morphological, molecular, and functional changes during metamorphosis of the olfactory system. We have previously described several novel features of the olfactory system of Xenopus laevis tadpoles, which all reflect the evolutionary transition point of this species, chief among them the exclusive expression of a large group of V2R receptors in the larval MOE, co-localized with functional amino acid responses. Thus the amphibian V2R family is divided between vomeronasal and main olfactory epithlium, a very unusual feature. Here we suggest to study the development of this feature during metamorphosis, together with an analysis of amino acid odor responses in both main noses generated during metamorphosis, the principal and the middle cavity (air nose and water nose, respectively). To complement these studies we suggest two independent approaches to deorphanize Xenopus V2R receptors, measuring odor responses of V2Rs heterologously expressed in Xenopus oocytes, and in vivo imaging after knockout of an essential co-receptor for V2Rs.