Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources (Shanghai Ocean University), Ministry of Education; International Research Center for Marine Biosciences at Shanghai Ocean University, Ministry of Science and Technology; National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, Shanghai, 201306, China.
BMC Genomics. 2022 Aug 3;23(1):553. doi: 10.1186/s12864-022-08787-z.
Tetrodotoxin (TTX) is a deadly neurotoxin and usually accumulates in large amounts in the ovaries but is non-toxic or low toxic in the testis of pufferfish. The molecular mechanism underlying sexual dimorphism accumulation of TTX in ovary and testis, and the relationship between TTX accumulation with sex related genes expression remain largely unknown. The present study investigated the effects of exogenous TTX treatment on Takifugu flavidus. The results demonstrated that exogenous TTX administration significantly incresed level of TTX concentration in kidney, cholecyst, skin, liver, heart, muscle, ovary and testis of the treatment group (TG) than that of the control group (CG). Transcriptome sequencing and analysis were performed to study differential expression profiles of mRNA and piRNA after TTX administration of the ovary and testis. The results showed that compared with female control group (FCG) and male control group (MCG), TTX administration resulted in 80 and 23 piRNAs, 126 and 223 genes up and down regulated expression in female TTX-treated group (FTG), meanwhile, 286 and 223 piRNAs, 2 and 443 genes up and down regulated expression in male TTX-treated group (MTG). The female dominant genes cyp19a1, gdf9 and foxl2 were found to be up-regulated in MTG. The cyp19a1, whose corresponding target piRNA uniq_554482 was identified as down-regulated in the MTG, indicating the gene expression feminization in testis after exogenous TTX administration. The KEGG enrichment analysis revealed that differentially expressed genes (DEGs) and piRNAs (DEpiRNAs) in MTG vs MCG group were more enriched in metabolism pathways, indicating that the testis produced more metabolic pathways in response to exogenous TTX, which might be a reason for the sexual dimorphism of TTX distribution in gonads. In addition, TdT-mediated dUTP-biotin nick end labeling staining showed that significant apoptosis was detected in the MTG testis, and the role of the cell apoptotic pathways was further confirmed. Overall, our research revealed that the response of the ovary and testis to TTX administration was largely different, the ovary is more tolerant whereas the testis is more sensitive to TTX. These data will deepen our understanding on the accumulation of TTX sexual dimorphism in Takifugu.
河豚毒素（TTX）是一种致命的神经毒素，通常在河豚鱼的卵巢中大量积累，但在睾丸中则无毒或低毒。卵巢和睾丸中 TTX 积累的性别二态性的分子机制，以及 TTX 积累与性别相关基因表达之间的关系在很大程度上仍然未知。本研究调查了外源性 TTX 处理对黄鳍东方鲀的影响。结果表明，与对照组（CG）相比，TTX 处理组（TG）的肾脏、胆囊、皮肤、肝脏、心脏、肌肉、卵巢和睾丸中的 TTX 浓度明显升高。对卵巢和睾丸 TTX 处理后的 mRNA 和 piRNA 的差异表达谱进行了转录组测序和分析。结果表明，与雌鱼对照组（FCG）和雄鱼对照组（MCG）相比，TTX 处理导致雌鱼 TTX 处理组（FTG）中 80 个和 23 个 piRNA、126 个和 223 个基因上调和下调表达，同时，雄鱼 TTX 处理组（MTG）中 286 个和 223 个 piRNA、2 个和 443 个基因上调和下调表达。发现优势基因 cyp19a1、gdf9 和 foxl2 在 MTG 中上调。cyp19a1 的相应靶标 piRNA uniq_554482 在 MTG 中被鉴定为下调，表明外源性 TTX 处理后睾丸的基因表达出现女性化。KEGG 富集分析表明，MTG 与 MCG 组相比，差异表达基因（DEGs）和 piRNA（DEpiRNAs）在代谢途径中更为丰富，表明睾丸对外源性 TTX 产生了更多的代谢途径，这可能是 TTX 在性腺中分布存在性别二态性的原因。此外，TdT 介导的 dUTP-生物素 nick end labeling 染色显示，MTG 睾丸中检测到明显的细胞凋亡，进一步证实了细胞凋亡途径的作用。总的来说，我们的研究表明，卵巢和睾丸对 TTX 处理的反应存在很大差异，卵巢对 TTX 更耐受，而睾丸对 TTX 更敏感。这些数据将加深我们对河豚鱼 TTX 积累的性别二态性的理解。
