Structural analysis, selection, and ontogeny of the shark new antigen receptor (IgNAR): identification of a new locus preferentially expressed in early development
Structural analysis, selection, and ontogeny of the shark new antigen receptor (IgNAR): identification of a new locus preferentially expressed in early development
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DOI：
10.1007/s00251-002-0479-z
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发表时间：
2002-10-01
期刊：
影响因子：
3.2
通讯作者：
Flajnik, MF
中科院分区：
文献类型：
--
作者：
Diaz, M;Stanfield, RL;Flajnik, MF
新的抗原受体（IgNAR）家族已在迄今为止研究的所有软骨鱼物种中检测到，并且具有一些有趣的结构和功能特征。 IgNAR 蛋白以跨膜和分泌形式存在，是没有相关轻链的重链二聚体，二聚体的每条链都有一个自由且灵活的 V 区。四个重排事件（IV、3D 和 1J 种系基因之间）产生表达的 NAR V 基因，从而产生包含半胱氨酸残基的长且多样化的 CDR3 区域。 IgNAR 突变频率非常高，并且“选择性”突变仅在编码分泌形式的基因中发现，表明主要库完全基于 CDR3。在这里，我们进一步分析了两种 IgNAR 类型，即 CDR3 中具有 1 个半胱氨酸的“1 型”和具有偶数（2 个或 4 个）CDR3 半胱氨酸的“2 型”，并发现 IgNAR V 结构域中二硫键的放置对 CDRI 和 CDR2 中突变的选择有不同的影响。个体发育分析表明，幼年动物的 IgNAR 序列很少发生突变，这与鲨鱼免疫系统必须成熟才能发生伴随选择的高水平突变的范式一致。尽管如此，也与 Ig-NAR 库完全基于 CDR3 的观点一致，但与大多数其他脊椎动物的研究不同，N 区多样性存在于出生时表达的 IgNAR 克隆中。在对这一早期 IgNAR 库的研究过程中，我们偶然发现了第三种类型的 IgNAR 基因，该基因在所有新生儿组织中表达；在生命后期，它的表达仅在外角器官中持续存在，该组织最近被证明是软骨鱼中的（？）初级淋巴组织。这种“3型”IgNAR基因仍然经历三个重排事件（两个D区“种系连接”），但CDR3序列具有完全相同的长度和非常相似的序列，表明“3型”CDR3在个体发育早期被选择，可能是通过自配体选择的。
The new antigen receptor (IgNAR) family has been detected in all elasmobranch species so far studied and has several intriguing structural and functional features. IgNAR protein, found in both transmembrane and secretory forms, is a dimer of heavy chains with no associated light chains, with each chain of the dimer having a single free and flexible V region. Four rearrangement events (among IV, 3D, and 1J germline genes) generate an expressed NAR V gene, resulting in long and diverse CDR3 regions that contain cysteine residues. IgNAR mutation frequency is very high and "selected" mutations are found only in genes encoding the secreted form, suggesting that the primary repertoire is entirely CDR3-based. Here we further analyzed the two IgNAR types, "type 1" having one cysteine in CDR3 and "type 2" with an even number (two or four) of CDR3 cysteines, and discovered that placement of the disulfide bridges in the IgNAR V domain differentially influences the selection of mutations in CDRI and CDR2. Ontogenetic analyses showed that IgNAR sequences from young animals were infrequently mutated, consistent with the paradigm that the shark immune system must become mature before high levels of mutation accompanied with selection can occur. Nevertheless, also in agreement with the idea that the Ig-NAR repertoire is entirely CDR3-based, but unlike studies in most other vertebrates, N-region diversity is present in expressed IgNAR clones at birth. During the investigation of this early IgNAR repertoire we serendipitously detected a third type of IgNAR gene that is expressed in all neonatal tissues; later in life its expression is perpetuated only in the epigonal organ, a tissue recently shown to be a (the?) primary lymphoid tissue in elasmobranchs. This "type 3" IgNAR gene still undergoes three rearrangement events (two D regions are "germline-joined"), yet CDR3 sequences were exactly of the same length and very similar sequence, suggesting that "type 3" CDR3s are selected early in ontogeny, perhaps by a self-ligand.