Camelids are characterized by their unique adaptive immune system that exhibits the generation of homodimeric heavy-chain immunoglobulins, somatic hypermutation of T-cell receptors, and low genetic diversity of major histocompatibility complex (MHC) genes. However, short-read assemblies are typically highly fragmented in these gene loci owing to their repetitive and polymorphic nature. Here, we constructed a chromosome-level assembly of wild Bactrian camel genome based on high-coverage long-read sequencing and chromatin interaction mapping. The assembly with a contig N50 of 5.37 Mb and a scaffold N50 of 76.03 Mb, represents the most contiguous camelid genome to date. The genomic organization of immunoglobulin heavy-chain locus was similar between the wild Bactrian camel and alpaca, and genes encoding for conventional and heavy-chain antibodies were intermixed. The organizations of two immunoglobulin light-chain loci and four T cell receptor loci were also fully deciphered using the new assembly. Additionally, the complete classical MHC region was resolved into a single contig. The high-quality assembly presented here provides an essential reference for future investigations examining the camelid immune system.

中文翻译：

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野生双峰驼基因组的染色体水平组装揭示了免疫基因位点的组织。

骆驼的特征在于其独特的适应性免疫系统，该系统具有同型二聚体重链免疫球蛋白的产生，T细胞受体的体细胞超突变以及主要组织相容性复合体（MHC）基因的低遗传多样性。但是，由于其重复性和多态性，短读装配通常在这些基因座中高度片段化。在这里，我们基于高覆盖率的长读测序和染色质相互作用图谱构建了野生双峰驼基因组的染色体级装配体。具有5.37 Mb重叠群N50和76.03 Mb支架N50的装配体代表了迄今为止最连续的骆驼科动物基因组。野生双峰驼和羊驼的免疫球蛋白重链基因座的基因组组织相似，将编码常规抗体和重链抗体的基因混合在一起。使用新的装配体还完全破译了两个免疫球蛋白轻链基因座和四个T细胞受体基因座的组织。此外，将完整的经典MHC区域解析为单个重叠群。这里展示的高质量组件为将来检查骆驼科动物免疫系统的研究提供了重要参考。