data_sheet_5_Diversity of Immunoglobulin Light Chain Genes in Non-Teleost Ray-Finned Fish Uncovers IgL Subdivision into Five Ancient Isotypes.PDF

The aim of this study was to fill important gaps in the evolutionary history of immunoglobulins by examining the structure and diversity of IgL genes in non-teleost ray-finned fish. First, based on the bioinformatic analysis of recent transcriptomic and genomic resources, we experimentally characterized the IgL genes in the chondrostean fish, Acipenser ruthenus (sterlet). We show that this species has three loci encoding IgL kappa-like chains with a translocon-type gene organization and a single VJC cluster, encoding homogeneous lambda-like light chain. In addition, sterlet possesses sigma-like VL and J-CL genes, which are transcribed separately and both encode protein products with cleavable leader peptides. The Acipenseriformes IgL dataset was extended by the sequences mined in the databases of species belonging to other non-teleost lineages of ray-finned fish: Holostei and Polypteriformes. Inclusion of these new data into phylogenetic analysis showed a clear subdivision of IgL chains into five groups. The isotype described previously as the teleostean IgL lambda turned out to be a kappa and lambda chain paralog that emerged before the radiation of ray-finned fish. We designate this isotype as lambda-2. The phylogeny also showed that sigma-2 IgL chains initially regarded as specific for cartilaginous fish are present in holosteans, polypterids, and even in turtles. We conclude that there were five ancient IgL isotypes, which evolved differentially in various lineages of jawed vertebrates.

本研究旨在通过解析非真骨辐鳍鱼（non-teleost ray-finned fish）的免疫球蛋白轻链（IgL, immunoglobulin light chain）基因的结构与多样性，填补免疫球蛋白进化史中的关键空白。首先，基于对最新转录组与基因组资源的生物信息学分析，我们对软骨硬鳞鱼（chondrostean fish）——西伯利亚鲟（Acipenser ruthenus, sterlet）的IgL基因开展了实验鉴定。结果显示，该物种拥有3个编码类kappa轻链的基因座，其基因组织为易位型基因组织（translocon-type gene organization），且存在1个VJC簇，可编码均一的类lambda轻链。此外，西伯利亚鲟还携带sigma样VL与J-CL基因，二者分别进行转录，且均能编码带有可裂解前导肽的蛋白产物。我们通过从其他非真骨辐鳍鱼谱系（包括全骨鱼下纲Holostei和多鳍鱼目Polypteriformes）的物种数据库中挖掘序列，扩充了鲟形目（Acipenseriformes）的IgL数据集。将这些新数据纳入系统发育分析（phylogenetic analysis）后，结果清晰显示IgL链可划分为5个类群。此前被归类为真骨鱼IgL lambda型的同种型，实则为kappa与lambda轻链的旁系同源物（paralog），其起源早于辐鳍鱼的辐射演化（radiation），我们将该同种型命名为lambda-2。系统发育分析还揭示，最初被认为是软骨鱼类特有的sigma-2型IgL链，实则存在于全骨鱼、多鳍鱼甚至龟类中。综上，本研究证实曾存在5种古老的IgL同种型，它们在有颌脊椎动物（jawed vertebrates）的不同谱系中发生了差异化演化。