Department of Biology, Lund University, Lund, Sweden.
Sci Rep. 2019 Dec 20;9(1):19506. doi: 10.1038/s41598-019-55800-9.
Passerine birds belong to the most species rich bird order and are found in a wide range of habitats. The extremely polymorphic adaptive immune system of passerines, identified through their major histocompatibility complex class I genes (MHC-I), may explain some of this extreme radiation. Recent work has shown that passerines have higher numbers of MHC-I gene copies than other birds, but little is currently known about expression and function of these gene copies. Non-passerine birds have a single highly expressed MHC-I gene copy, a pattern that seems unlikely in passerines. We used high-throughput sequencing to study MHC-I alleles in siskins (Spinus spinus) and determined gene expression, phylogenetic relationships and sequence divergence. We verified between six and 16 MHC-I alleles per individual and 97% of these were expressed. Strikingly, up to five alleles per individual had high expression. Out of 88 alleles 18 were putatively non-classical with low sequence divergence and expression, and found in a single phylogenetic cluster. The remaining 70 alleles were classical, with high sequence divergence and variable degrees of expression. Our results contradict the suggestion that birds only have a single dominantly expressed MHC-I gene by demonstrating several highly expressed MHC-I gene copies in a passerine.
雀形目鸟类属于物种最丰富的鸟类目之一，广泛分布于各种生境中。雀形目鸟类具有极其多样的适应性免疫系统，这可以通过它们的主要组织相容性复合体 I 类基因（MHC-I）来识别，这可能解释了这种极端辐射的部分原因。最近的研究表明，雀形目鸟类的 MHC-I 基因拷贝数高于其他鸟类，但目前对于这些基因拷贝的表达和功能知之甚少。非雀形目鸟类只有一个高度表达的 MHC-I 基因拷贝，这种模式在雀形目鸟类中似乎不太可能。我们使用高通量测序研究了锡嘴雀（Spinus spinus）的 MHC-I 等位基因，并确定了基因表达、系统发育关系和序列差异。我们在每个个体中检测到 6 到 16 个 MHC-I 等位基因，其中 97%得到了表达。引人注目的是，每个个体中多达 5 个等位基因具有高表达水平。在 88 个等位基因中，有 18 个被认为是非经典的，具有低序列差异和表达水平，并且存在于单个系统发育群中。其余 70 个等位基因为经典型，具有高序列差异和不同程度的表达。我们的研究结果与鸟类只有一个主要表达的 MHC-I 基因的观点相矛盾，表明在雀形目鸟类中存在多个高表达的 MHC-I 基因拷贝。
