College of Life Science, Sichuan Agricultural University, Ya'an 625014, China.
Genes (Basel). 2022 Jul 29;13(8):1360. doi: 10.3390/genes13081360.
Metamorphosis is a critical stage in the adaptive development of amphibians from aquatic to terrestrial animals. Metamorphosis of the Chinese giant salamander is mainly manifested by the loss of external gills with consequent changes in the respiratory pattern. The loss of the external gill is regulated by the pathway of apoptosis in which caspase genes are the key factors. This study cloned and expressed the of the Chinese giant salamander. The main results were as follows: the complete open reading frames (ORFs) were 885 bp, 960 bp, 1461 bp and 1279 bp, respectively; all contained the CASc domain, and most of the motifs were located in CASc domain; and caspase 8 possessed two DED structural domains and caspase 9 possessed a CARD structural domain. Furthermore, results from the tissue distribution analysis indicated that were all significantly expressed in the external gill, and at 9 and 10 months of age (MOA), which is the peak time for the loss, the EXPRESSION level of was obviously high, which was consistent with the histological result. Moreover, the loss of external gills of the Chinese giant salamander may result from activation of both the apoptosis-related death receptor pathway and the mitochondrial pathway. Finally, it was discovered that thyroid hormone (TH) treatment could both advance the time point at which the external gills of the Chinese giant salamander began to degenerate and shorten this process. Interestingly, at the peak of its metamorphosis (9 MOA), the Chinese giant salamander further accelerated the metamorphosis rate of TH treatment, which suggested a promotive effect on the loss of external gills via the superimposition of the exogenous TH and genes. The study of genes in this experiment was conducive to understanding the mechanism of external gill loss in the Chinese giant salamander, as well as improving our understanding of the metamorphosis development of some Caudata species.
变态是两栖动物从水生到陆生动物适应性发育的关键阶段。中国大鲵的变态主要表现为外部鳃的丧失，进而导致呼吸模式的改变。外部鳃的丧失是由凋亡途径调节的，其中半胱氨酸蛋白酶基因是关键因素。本研究克隆并表达了中国大鲵的。主要结果如下：完整的开放阅读框（ORF）分别为 885bp、960bp、1461bp 和 1279bp；均含有 CASc 结构域，大部分基序位于 CASc 结构域内；caspase 8 具有两个 DED 结构域，caspase 9 具有 CARD 结构域。此外，组织分布分析结果表明，在外部鳃中均有明显表达，在 9 月龄（MOA）和 10 月龄（MOA），即外部鳃丧失的高峰期，的表达水平明显较高，与组织学结果一致。此外，中国大鲵外部鳃的丧失可能是由于凋亡相关死亡受体途径和线粒体途径的激活。最后发现，甲状腺激素（TH）处理既能提前中国大鲵外部鳃开始退化的时间点，又能缩短这一过程。有趣的是，在其变态高峰期（9MOA），中国大鲵进一步加速了 TH 处理的变态率，这表明通过外源性 TH 和基因的叠加对外部鳃的丧失有促进作用。本实验对半胱氨酸蛋白酶基因的研究有助于了解中国大鲵外部鳃丧失的机制，也有助于提高我们对某些有尾类物种变态发育的认识。
