Metz Juriaan R, Peters Joris J M, Flik Gert
Department Organismal Animal Physiology, Institute for Neuroscience, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.
Gen Comp Endocrinol. 2006 Sep 1;148(2):150-62. doi: 10.1016/j.ygcen.2006.03.001. Epub 2006 Apr 18.
The melanocortin system consists of melanocortin peptides derived from the proopiomelanocortin gene (in particular adrenocorticotropic hormone, ACTH, and melanocyte-stimulating hormones, MSH) and five melanocortin receptor subtypes (MC1R-MC5R). Knowledge of the melanocortin system in fish is still limited, but information on the receptor part of the system is very rapidly growing. The melanocortin receptors (MCRs) have been recently cloned from several species of fish. The amino acid sequences appear remarkably well conserved. Pharmacological characterisation studies of the first identified piscine MCRs indicate that ACTH may be the original ligand for the MCRs, while the MSH peptides gained specialised functions in the course of evolution. Considering the tissue distribution of the MCRs, there are two distinctions between mammals and fish: where in mammals the MC4R is exclusively expressed in the central nervous system, in the fish species examined so far it is also peripherally expressed. It does however, alike the situation in mammals, likely play a key role in the central regulation of food intake and energy balance. Not only the MCRs, but also many other factors involved herewith, have been found in fish and roughly appear to function similarly as in mammals. The second difference is the distribution of the MC5R, which appears less widely expressed in fish than in mammals. Considering the available data it is predicted that, in mammals and fish alike, skin colouration is mediated via MC1R and steroidogenesis via MC2R. This review provides a short overview of the basic molecular characteristics, pharmacology, and tissue distribution of the MCRs in the fish investigated up to now, as well as their physiological role in the processes of skin colouration, steroidogenesis, and feeding behaviour.
黑皮质素系统由源自阿黑皮素原基因的黑皮质素肽（特别是促肾上腺皮质激素、促肾上腺皮质激素，以及促黑素细胞激素、促黑素细胞激素）和五种黑皮质素受体亚型（MC1R - MC5R）组成。鱼类黑皮质素系统的知识仍然有限，但该系统受体部分的信息正在迅速增长。黑皮质素受体（MCRs）最近已从几种鱼类中克隆出来。其氨基酸序列显示出非常好的保守性。对最初鉴定的鱼类MCRs的药理学特性研究表明，促肾上腺皮质激素可能是MCRs的原始配体，而促黑素细胞激素肽在进化过程中获得了特殊功能。考虑到MCRs的组织分布，哺乳动物和鱼类之间存在两个区别：在哺乳动物中，MC4R仅在中枢神经系统中表达，而在迄今为止研究的鱼类物种中，它也在外周表达。然而，与哺乳动物的情况一样，它可能在食物摄入和能量平衡的中枢调节中起关键作用。不仅在鱼类中发现了MCRs，还发现了许多与之相关的其他因素，它们的功能大致与哺乳动物相似。第二个区别是MC5R的分布，它在鱼类中的表达似乎比在哺乳动物中更不广泛。根据现有数据预测，在哺乳动物和鱼类中，皮肤色素沉着均通过MC1R介导，而类固醇生成则通过MC2R介导。本综述简要概述了迄今为止所研究鱼类中MCRs的基本分子特征、药理学和组织分布，以及它们在皮肤色素沉着、类固醇生成和摄食行为过程中的生理作用。
