尼罗罗非鱼Siglec-4b like基因的克隆与表达特性分析

从尼罗罗非鱼(Oreochromis niloticus)嗜中性粒细胞中克隆了唾液酸结合型免疫球蛋白凝集素 Siglec-4b like基因，对其进行生物信息学分析，并利用实时荧光定量PCR检测：1)早期胚胎发育过程的表达；2)成鱼组织中的分布；3)人工感染无乳链球菌（Streptococcus agalactiae, GBS）后组织表达的变化。结果表明，尼罗罗非鱼Siglec-4b like具有与哺乳类Siglec-4相似的特异性结构域及保守氨基酸残基；早期胚胎发育Siglec-4b like基因在卵子中有一定表达量，受精后7 h 即卵裂期表达上调，随后表达下降；Siglec-4b like基因在所检测的各组织中均有表达，鳃的表达量最高，其次是肌肉、皮肤、头肾和肠，其他组织的表达量较低；人工感染无乳链球菌后，Siglec-4b like在鳃、肾与肠等多个组织的表达均呈下调趋势。研究结果为进一步开展Siglec-4b like对罗非鱼免疫系统的调控作用及其与无乳链球菌免疫逃逸机制关系的研究奠定基础。

Cloning and expression pattern of Siglec-4b like in Oreochromis niloticus

We cloned the sialic acid-binding immunoglobulin superfamily lectin Siglec-4b like gene from neutrophilic granulocyte of Oreochromis niloticus, and then analyzed its sequence by bioinformatics approach and detected its mRNA expression levels during embryonic development and in tissues before and after artificial infection of Streptococcus agalactiae (GBS) by qPCR. The analysis shows that Siglec-4b like had specific domains and conservative amino acid residues similar to mammalian Siglec-4. During the embryonic development, a certain amount of Siglec-4b like expressed in eggs, and the expression increased after fertilization. As embryo developed, the expression continued to rise and reached the maximum amount at 7 hpf and then decreased gradually. Siglec-4b like mRNA was ubiquitously expressed in all the tested tissues of tilapia, and the expression levels were relatively high in gill, muscle, skin, head kidneys and intestines but very low in the other tested tissues. After being infected with GBS, the expression of Siglec-4b like in gill, head kidneys, intestines, muscle and skin decreased. The results provide references for further research on immune escape mechanism of GBS and regulation effect of Siglec-4b like on tilapia immune system.