Immunoglobulins (Igs) are fundamental components of the adaptive immune system of vertebrates, with the IgT/IgZ isotype specific of Teleosts. In this paper we describe the identification of an IgT heavy chain from the European sea bass (Dicentrarchus labrax L.), its molecular characterization and tissue mRNA localization by in situ hybridization. Sea bass IgT consists of 552 aa (Accession Number KM410929) and it contains a putative 19 amino acids long signal peptide and one potential N-glycosylation site. The C-region consists of four CH domains; each contains the cysteine and tryptophan residues required for their correct folding. Based on the recent sequencing of sea bass genome, we have identified five different genomic contigs bearing exons unequivocally pertaining to IgT (CH2, CH3 and CH4), but none corresponded to a complete IgH locus as IgT sequences were found in the highly fragmented assembled genomic regions which could not be assigned to any major scaffold. The 3D structure of sea bass IgT has been modelled using the crystal structure of a mouse Ig gamma as a template, thus showing that the amino acid sequence is suitable for the expected topology referred to an immunoglobulin-like architecture. The basal expression of sea bass IgT and IgM in different organs has been analysed: gut and gills, important mucosal organs, showed high IgT transcripts levels and this was the first indication of the possible involvement of sea bass IgT in mucosal immune responses. Moreover, sea bass IgT expression increased in gills and spleen after infection with nodavirus, highlighting the importance of IgT in sea bass immune responses. In situ hybridization confirmed the presence of IgT transcripts in the gut and it revealed a differential expression along the intestinal tract, with a major expression in the posterior intestine, suggesting the hindgut as a site for the recruitment of IgT+ cells in this species. IgT transcripts were also found in gill filaments and parallel lamellae and, for the first time, we identified scattered IgT positive cells in the liver, with a strong signal in the hepatic parenchyma. In conclusion, we performed a full molecular characterization of IgT in sea bass that points out its possible involvement in mucosal immune responses of this species.

中文翻译：

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鲈鱼（Dicentrarchus labrax L.）的免疫球蛋白T：诺达病毒感染后的分子表征，组织定位和表达。

免疫球蛋白（Igs）是脊椎动物适应性免疫系统的基本组成部分，Teleosts具有特定的IgT / IgZ同种型。在本文中，我们描述了从欧洲鲈鱼（Dicentrarchus labrax L.）鉴定IgT重链的方法，分子特征以及通过原位杂交对组织mRNA进行定位。鲈鱼IgT由552个氨基酸组成（登录号KM410929），它包含一个假定的19个氨基酸长的信号肽和一个潜在的N-糖基化位点。C区由四个CH域组成；每个都包含正确折叠所需的半胱氨酸和色氨酸残基。根据最近对鲈鱼基因组进行的测序，我们确定了五个明确带有IgT外显子的不同基因组重叠群（CH2，CH3和CH4），但是没有一个对应于完整的IgH基因座，因为在高度片段化的组装基因组区域中发现了IgT序列，而该基因组区域无法分配给任何主要支架。已经使用小鼠Igγ的晶体结构作为模板对海鲈IgT的3D结构进行了建模，从而表明该氨基酸序列适合于称为免疫球蛋白样结构的预期拓扑。分析了鲈鱼IgT和IgM在不同器官中的基础表达：重要粘膜器官的肠和腮显示出高的IgT转录物水平，这是鲈鱼IgT可能参与粘膜免疫反应的第一个迹象。此外，感染诺达病毒后，鲈鱼IgT表达在g和脾脏中增加，突显了IgT在鲈鱼免疫反应中的重要性。原位杂交证实了肠道中存在IgT转录物，并揭示了沿肠道的差异表达，主要在后肠中表达，表明后肠是该物种中IgT +细胞募集的位点。在g丝和平行片状细胞中也发现了IgT转录本，我们首次在肝脏中发现了散布的IgT阳性细胞，在肝实质中有很强的信号。总之，我们在鲈鱼中进行了IgT的完整分子表征，指出其可能参与了该物种的粘膜免疫反应。提示后肠是该物种中IgT +细胞募集的位点。在g丝和平行片状细胞中也发现了IgT转录本，我们首次在肝脏中发现了散布的IgT阳性细胞，在肝实质中有很强的信号。总之，我们在鲈鱼中进行了IgT的完整分子表征，指出其可能参与了该物种的粘膜免疫反应。提示后肠是该物种中IgT +细胞募集的位点。在g丝和平行片状细胞中也发现了IgT转录本，我们首次在肝脏中发现了散布的IgT阳性细胞，在肝实质中有很强的信号。总之，我们在鲈鱼中进行了IgT的完整分子表征，指出其可能参与了该物种的粘膜免疫反应。