Expression and phylogenetic analyses reveal paralogous lineages of putatively classical and non-classical MHC-I genes in three sparrow species (Passer)

Background: The Major Histocompatibility Complex (MHC) plays a central role in immunity and has been given considerable attention by evolutionary ecologists due to its associations with fitness-related traits. Songbirds have unusually high numbers of MHC class I (MHC-I) genes, but it is not known whether all are expressed and equally important for immune function. Classical MHC-I genes are highly expressed, polymorphic and present peptides to T-cells whereas non-classical MHC-I genes have lower expression, are more monomorphic and do not present peptides to T-cells. To get a better understanding of the highly duplicated MHC genes in songbirds, we studied gene expression in a phylogenetic framework in three species of sparrows (house sparrow, tree sparrow and Spanish sparrow), using high-throughput sequencing. We hypothesize that sparrows could have classical and non-classical genes, as previously indicated though never tested using gene expression.
Results: The phylogenetic analyses re...

研究背景：主要组织相容性复合体（Major Histocompatibility Complex, MHC）在免疫反应中发挥核心作用，因其与适合度相关性状存在关联，故而受到进化生态学家的广泛关注。鸣禽的MHC I类（MHC class I, MHC-I）基因数量异乎寻常地多，但目前尚不清楚其中所有基因是否均会表达，且对免疫功能具有同等重要的作用。经典MHC-I基因呈高表达状态，具有高度多态性，可将抗原肽呈递给T细胞；而非经典MHC-I基因则表达水平较低、多态性更低，且无法将抗原肽呈递给T细胞。为深入解析鸣禽中高度重复的MHC基因家族，我们以高通量测序技术为手段，基于系统发育框架对3种雀科鸟类（家麻雀、树麻雀以及西班牙麻雀）开展了基因表达研究。我们推测，麻雀类群可能同时存在经典与非经典MHC-I基因，这一推论虽在以往研究中有所提及，却从未借助基因表达实验得到验证。研究结果：系统发育分析结果显示……