Nitrogen metabolism and excretion in fish: integration from behaviour to genes

所有动物在消化食物或正常维持体内蛋白质的过程中都会产生废氮作为氨。氨对神经系统是有毒的，只要人体血液中氨浓度增加一倍（例如，可能在肝脏或肾脏疾病中看到），最终就会导致昏迷和死亡。因此，所有动物要么直接将氨排出体外（如水生动物可能排出到水中），要么将其解毒为毒性较小的化合物，以更浓缩的形式排出体外（如尿素，如许多陆生动物，包括人类）。人们曾经认为，在鱼类等水生物种中，产生尿素的基因之所以不表达，是因为在氨直接排泄占主导地位的水生环境中不需要它们。然而，最近几十年的研究表明，这些基因实际上是（可能是大多数）胚胎鱼所需要的，而且在某些鱼类成年后很少使用。拟议的研究考察了这样一个鱼类家族，蟾蜍鱼和海军军官，其中包括一些特定的成员，它们制造和排泄尿素作为一种含氮废物。该小组将被用来研究一种新的假设，即尿素被用来“掩盖”蟾蜍鱼的气味，使潜在的捕食者无法察觉。在胃肠道、鳃和神经系统中，允许蟾鱼以离散脉冲控制尿素排泄的精确机制将被研究。此外，参与尿素和氨的运输和代谢的几个关键基因的作用将被研究，包括所谓的恒河蛋白（在人类中负责输血中重要的“Rh因子”）。该研究最终可能在鱼类养殖中得到应用。

All animals produce waste nitrogen as ammonia when they digest a meal, or in the normal maintenance of body protein. Ammonia is toxic to the nervous system, and as little as a doubling of blood ammonia levels in humans (e.g., as might be seen in liver or kidney disease) can eventually lead to coma and death. Therefore, all animals must either excrete ammonia directly (to the water as is possible in aquatic animals) or detoxify it to a less toxic compound for excretion in a more concentrated form (e.g., urea, as in many terrestrial animals, including humans). It was once thought that the genes for urea production in aquatic species like fish were not expressed because they were not needed in an aquatic environment where direct excretion of ammonia predominates. However, research in recent decades has shown that these genes are in fact needed in (probably most) embryonic fish, and are also used rarely by some species of fish as adults. The proposed research examines one such family of fishes, the toadfish and midshipmen, that contains selected members that make and excrete urea as a nitrogenous waste product. The group will be used to study a novel hypothesis that urea is use to 'cloak' the scent of toadfish to potential predators. The precise mechanisms in the gastrointestinal tract, gills and nervous system that allow toadfish to control urea excretion in discrete pulses will be examined. Furthermore, the action of several key genes involved in transport and metabolism of urea and ammonia will be studied, including the so-called Rhesus proteins (which in humans are responsible for the "Rh factors" important in blood transfusions). The research may eventually have application in fish aquaculture.