Rag1 and rag2 gene expressions identify lymphopoietic tissues in juvenile and adult Chinese giant salamander (Andrias davidianus)

Rag1 and rag2 are two closely linked recombination activating genes required for V(D)J recombination of antigen receptors in immature lymphocytes, whose expression can serve as marker to identify the lymphopoietic tissues. To study the development of lymphopoietic tissues in Chinese giant salamander (Andrias davidianus), the Chinese giant salamander rag1 and rag2 coding sequences were cloned and determined. High transcript levels of rag1 and rag2 were co-detected in the thymus before 14 months of age, whereas levels were lower in spleen, liver and kidney at all stage of development. The spatial expression patterns of rag1 and rag2 were studied in combination with igY and tcr beta gene expression using in situ hybridization. Significant transcript signals for rag1, rag2, tcr beta and igY were detected not only in the thymus and spleen but also the liver and kidney of juvenile and adult Chinese giant salamanders, which suggests that cells of lymphocyte lineage are present in multiple tissues of the Chinese giant salamander. This implies that lymphopoiesis may take place in these tissues. The tissue morphology of thymus suggested that the branched thymic primordium developed into mature organ with the development of thymocyte from juvenile to adult. These results not only confirm that as expected the thymus and spleen are primordial lymphopoietic tissues but also suggest that the liver and kidney provide site of lymphocyte differentiation in Chinese giant salamander.

Rag1和Rag2是未成熟淋巴细胞中抗原受体V(D)J重组所必需的两个紧密连锁的重组激活基因，其表达可作为识别淋巴生成组织的标志物。为了研究中国大鲵（Andrias davidianus）淋巴生成组织的发育情况，对中国大鲵的Rag1和Rag2编码序列进行了克隆和测定。在14月龄前的胸腺中同时检测到较高水平的Rag1和Rag2转录本，而在发育的各个阶段，脾脏、肝脏和肾脏中的水平较低。利用原位杂交技术结合IgY和Tcrβ基因表达研究了Rag1和Rag2的空间表达模式。不仅在幼年和成年中国大鲵的胸腺和脾脏中，而且在肝脏和肾脏中都检测到了Rag1、Rag2、Tcrβ和IgY的显著转录信号，这表明淋巴细胞谱系的细胞存在于中国大鲵的多个组织中。这意味着淋巴生成可能发生在这些组织中。胸腺的组织形态表明，随着胸腺细胞从幼年到成年的发育，分支的胸腺原基发育成为成熟器官。这些结果不仅证实了胸腺和脾脏如预期的那样是原始淋巴生成组织，还表明肝脏和肾脏为中国大鲵的淋巴细胞分化提供了场所。