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Published on: August 8, 2020
Transcriptome analysis revealed gene expression feminization of testis after exogenous tetrodotoxin administration in
Xue He1, Hexing Wu1, Yaping Ye1
1Key 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.
Abstract:
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.
Insights
This study reveals that pufferfish testes are more sensitive to tetrodotoxin (TTX) than ovaries, showing feminization and apoptosis after TTX exposure. This helps explain the different accumulation of this deadly neurotoxin in male and female gonads.
Area of Science:
- Toxicology
- Molecular Biology
- Genomics
- Reproductive Biology
Background:
- Tetrodotoxin (TTX) is a potent neurotoxin known for its differential accumulation in pufferfish gonads, with higher concentrations typically found in ovaries than testes.
- The molecular mechanisms driving this sexual dimorphism in TTX accumulation and its relationship with sex-related gene expression remain largely unexplored.
Purpose of the Study:
- To investigate the effects of exogenous tetrodotoxin (TTX) administration on TTX accumulation and gene expression profiles in the pufferfish Takifugu flavidus.
- To elucidate the molecular basis for sexual dimorphism in TTX accumulation and its impact on reproductive tissues.
Main Methods:
- Exogenous TTX administration to Takifugu flavidus, followed by quantification of TTX levels across various tissues.
- Transcriptome sequencing (mRNA and piRNA) of ovary and testis tissues from control and TTX-treated groups.
- Bioinformatic analysis including differential gene and piRNA expression, KEGG enrichment analysis, and apoptosis assays (TUNEL staining).
Main Results:
- Exogenous TTX administration significantly increased TTX concentrations in all examined tissues, including gonads, in the treatment group.
- Differential expression analysis revealed significant changes in mRNA and piRNA profiles in both ovary and testis post-TTX treatment, with distinct patterns between sexes.
- Testis exposure to TTX led to the upregulation of female-dominant genes (e.g., cyp19a1) and downregulation of a key piRNA, suggesting gene expression feminization. Significant apoptosis was also observed in the male TTX-treated group.
Conclusions:
- Pufferfish testes exhibit higher sensitivity to exogenous TTX compared to ovaries, indicated by significant apoptosis and gene expression feminization.
- Differential enrichment in metabolism pathways in the male gonad in response to TTX may contribute to the observed sexual dimorphism in TTX distribution.
- These findings provide crucial insights into the differential accumulation of TTX in pufferfish gonads and highlight the distinct responses of male and female reproductive systems to this potent neurotoxin.
