Polymeric immunoglobulin receptor (pIgR) is an important member of the immunoglobulin superfamily. It can mediate polarity transportation of polymeric immunoglobulin in mucosal epithelial cells and play an important role in innate and acquired immunity. In this study, the full-length cDNA sequence of Carassius auratus indigentiaus pIgR gene was firstly cloned and characterized. The complete cDNA sequence of C. auratus indigentiaus pIgR gene is 1399 bp, including a 984 bp open reading frame that encodes 327 amino acids. The pIgR is composed of extracellular, transmembrane and intracellular regions, which are composed of 255, 23 and 49 amino acids, respectively. The extracellular region contains two Ig-like domains (ILDs), ILD1 consists of 104 amino acids (25–128) and ILD2 consists of 93 amino acids (137–229). The similarity between the pIgR sequences of C. auratus indigentiaus and other fish is 65.95%–97.55%. Analysis of phylogenetic trees shows that pIgR of C. auratus indigentiaus clusters into one branch with the pIgR of Cypriniformes. QRT-PCR analysis revealed that the pIgR gene expression was highest in liver, followed by intestine, gill, head kidney and skin. After challenge with Aeromonas hydrophila, the relative expressions of pIgR in different tissues first increased and then decreased within 96 h. Moreover, the expression of pIgR gene peaked earlier in mucosal immune tissues (intestines, gill and skin) than in system immune tissues. It suggested that pIgR might play an important role in mucosa-associated lymphoid tissue to protect the C. auratus indigentiaus against Aeromonas hydrophila infection.

中文翻译：

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东庭金鲫（Carassius auratus indigentiaus）中的聚合免疫球蛋白受体：响应嗜水气单胞菌攻击的分子特征和表达分析

聚合免疫球蛋白受体（pIgR）是免疫球蛋白超家族的重要成员。它可以介导聚合免疫球蛋白在黏膜上皮细胞中的极性转运，在先天性和获得性免疫中起重要作用。本研究首次克隆并鉴定了鲫鱼pIgR基因的全长cDNA序列。C. auratus indigentiaus的完整 cDNA 序列pIgR基因全长1399 bp，包括一个编码327个氨基酸的984 bp开放阅读框。pIgR由胞外区、跨膜区和胞内区组成，分别由255、23和49个氨基酸组成。细胞外区域包含两个 Ig 样结构域 (ILD)，ILD1 由 104 个氨基酸 (25-128) 组成，ILD2 由 93 个氨基酸 (137-229) 组成。C. auratus indigentiaus的pIgR序列与其他鱼类的相似度为65.95%~97.55%。系统发育树分析表明，C. auratus indigentiaus的pIgR与Cypriniformes的pIgR聚集成一个分支。QRT-PCR分析显示pIgR基因在肝脏中的表达量最高，其次是肠、鳃、头肾和皮肤。挑战后嗜水气单胞菌,96 h内pIgR在不同组织中的相对表达量先升高后降低。此外，pIgR基因在黏膜免疫组织（肠、鳃和皮肤）中的表达峰值比在系统免疫组织中更早。这表明 pIgR 可能在粘膜相关淋巴组织中发挥重要作用，以保护C. auratus indigentiaus免受嗜水气单胞菌感染。