Nitrogen excretion and acid-base regulation in invertebrate systems: Mechanisms, regulation and the specific role of Rh-proteins and AMTs.

氨是蛋白质代谢产生的剧毒废物。在含氨动物（例如水生无脊椎动物和鱼类）中，氨是直接排泄的，不会转化为毒性较小的分子，如尿素或尿酸，因此有效的排泄系统对于将细胞和体液氨水平保持在可容忍的范围内至关重要。虽然所有动物中约98%（= 30门）是无脊椎动物，但我们对这一优势群体的氮排泄策略和机制的了解相当少。该研究的目标是首先详细了解各种不同无脊椎动物群体的氨排泄途径和机制，包括环节动物（淡水水蛭）、线虫（土壤活蛔虫）、软体动物（淡水贻贝）、蛛形动物（海水马蹄蟹）和甲壳类动物（新鲜、咸淡和海水蟹）。本研究主要包括三个方面的研究目标：(1)水生无脊椎动物的实际排泄机制，探索共同的祖先排泄策略；(2)表达两种氨转运蛋白的过渡性动物秀丽隐杆线虫（Caenorhabditis elegans）的系统发育古细菌和植物“AMTs”及其远亲动物“rh蛋白”的进化与功能；(3)甲壳类动物氨排泄与酸碱平衡的关系，以及全球水体二氧化碳浓度升高和海洋酸化对广盐蟹ph调节的影响。这三个目标将为古代无脊椎动物系统发育中氨排泄机制和酸碱调节的进化提供新的见解，包括rh蛋白和amt作为NH3， CO2或H+通道的作用。预计将发现基本和一般的氮排泄和pH调节策略。了解氨排泄机制以及动物对环境氨水平升高的反应对于保护计划至关重要，这些计划旨在保护生活在受富含氨的农业径流威胁的水生栖息地的动物群落，并管理水产养殖设施。

Ammonia is a highly toxic waste product derived from protein metabolism. In ammoniotelic animals (e.g. aquatic invertebrates and fish), where ammonia is excreted directly and not transformed into less toxic molecules such as urea or uric acid, an effective excretion system is essential to keep cellular and body fluid ammonia levels within a tolerable range. Although ca. 98% (= 30 phyla) of all animals are invertebrates, our knowledge of nitrogen excretion strategies and mechanisms in this dominant group is rather diminutive. The goal of the proposed research is to gain first and detailed insights of ammonia excretion pathways and mechanisms in a wide variety of different invertebrate groups, including annelids (freshwater leeches), nematodes (soil living roundworms), mollusks (freshwater mussels), arachnids (seawater horseshoe crabs) and crustaceans (fresh-, brackish-, and seawater crabs). The proposed research consists of three main objectives, investigating: (1) the actual excretion mechanisms in aquatic invertebrates to explore common ancestral excretion strategies; (2) the evolution and function of the phylogenetic ancient bacterial and plant "AMTs" and the distantly related animal "Rh-proteins" in the soil nematode Caenorhabditis elegans, a transitional animal that expresses both types of ammonia transporters; (3) the relation of ammonia excretion and acid-base balance in crustaceans and the effects of predicted increases in global aquatic pCO2 levels and ocean acidification on the pH-regulation in euryhaline crabs. The three objectives will provide novel insights of the evolution of ammonia excretion mechanisms and acid-base regulation in phylogentic ancient invertebrates, including the roles of Rh-proteins and AMTs as NH3, CO2 or H+ -channels. It is expected that fundamental and general nitrogen excretion and pH regulatory strategies will be discovered. Understanding the ammonia excretion mechanisms as well as the animal's responses towards elevated environmental ammonia levels are crucial for conservation programs, which are intended to protect animal communities living in aquatic habitats threatened by ammonia-rich agricultural run-off and also to manage aquaculture facilities.