Shum B P, Guethlein L, Flodin L R, Adkison M A, Hedrick R P, Nehring R B, Stet R J, Secombes C, Parham P
Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
J Immunol. 2001 Mar 1;166(5):3297-308. doi: 10.4049/jimmunol.166.5.3297.
Rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) represent two salmonid genera separated for 15--20 million years. cDNA sequences were determined for the classical MHC class I heavy chain gene UBA and the MHC class II beta-chain gene DAB from 15 rainbow and 10 brown trout. Both genes are highly polymorphic in both species and diploid in expression. The MHC class I alleles comprise several highly divergent lineages that are represented in both species and predate genera separation. The class II alleles are less divergent, highly species specific, and probably arose after genera separation. The striking difference in salmonid MHC class I and class II evolution contrasts with the situation in primates, where lineages of class II alleles have been sustained over longer periods of time relative to class I lineages. The difference may arise because salmonid MHC class I and II genes are not linked, whereas in mammals they are closely linked. A prevalent mechanism for evolving new MHC class I alleles in salmonids is recombination in intron II that shuffles alpha 1 and alpha 2 domains into different combinations.
虹鳟（Oncorhynchus mykiss）和褐鳟（Salmo trutta）代表了两个已分离1500万至2000万年的鲑科属。测定了15条虹鳟和10条褐鳟的经典MHC I类重链基因UBA和MHC II类β链基因DAB的cDNA序列。这两个基因在两个物种中均具有高度多态性且呈二倍体表达。MHC I类等位基因包括几个高度分化的谱系，这些谱系在两个物种中均有体现且早于属的分离。II类等位基因分化程度较低，具有高度的物种特异性，可能是在属分离后出现的。鲑科MHC I类和II类进化的显著差异与灵长类动物的情况形成对比，在灵长类动物中，II类等位基因的谱系相对于I类谱系维持的时间更长。这种差异可能是因为鲑科MHC I类和II类基因不连锁，而在哺乳动物中它们紧密连锁。鲑科中进化出新的MHC I类等位基因的一种普遍机制是内含子II中的重组，该重组将α1和α2结构域改组为不同的组合。
