DNA methylation, the most widely studied and most well-understood epigenetic modification, has been reported to play crucial roles in diverse processes. Although it has been found that DNA methylation can modulate the expression of immune-related genes in teleosts, a systemic analysis of epigenetic regulation on teleost immunity has rarely been performed. In this research, we employed whole-genome bisulfite sequencing to investigate the genome-wide DNA methylation profiles in select disease-resistant Cynoglossus semilaevis (DR-CS, family 14L006) and disease-susceptible C. semilaevis (DS-CS, family 14L104) against Vibrio harveyi infection. The results showed that following selective breeding, DR-CS had higher DNA methylation levels and different DNA methylation patterns, with 3,311 differentially methylated regions and 6,456 differentially methylated genes. Combining these data with the corresponding transcriptome data, we identified several immune-related genes that exhibited differential expression levels that were modulated by DNA methylation. Specifically, DNA methylation of tumor necrosis factor–like and lipopolysaccharide-binding protein-like was significantly correlated with their expression and significantly contributed to the disease resistance of the selected C. semilaevis family. In conclusion, we suggest that artificial selection for disease resistance in Chinese tongue sole causes changes in DNA methylation levels in important immune-related genes and that these epigenetic changes are potentially involved in multiple immune responses in Chinese tongue sole.

Background:SDC2 methylation is a feasible biomarker for colorectal cancer detection. Its specificity for colorectal cancer is higher than 90%, but the sensitivity is normally lower than 90%. This study aims to improve the sensitivity of SDC2 detection through finding a high positive target from the false-negative samples of SDC2 detection based on analysis of the bowel subsite difference in methylation.Methods: Hypermethylated TFPI2 was identified in SDC2 hypomethylated colorectal cancer samples retrieved from TCGA database with the methylation level lower than 0.2. The methylation-specific PCR assay was developed and then evaluated using tissue samples (184 cancer and 54 healthy control samples) and stool samples (289 cancer, 190 adenoma, and 217 healthy control samples).Results:TFPI2 was hypermethylated in most SDC2 hypomethylated colorectal cancer samples. When the SDC2/TFPI2-combined PCR assay was performed in stool specimens, the AUC value of cancer vs. control was 0.98, with the specificity of 96.40% and sensitivity of 96.60%, and the AUC value of adenoma vs. control was 0.87, with the specificity of 95.70% and the sensitivity of 80.00%. The improvement in sensitivity was the most momentous in the left colon. As the detection index, the Ct value was better in improving the sensitivity of detection than the methylation level based on the 2−ΔΔCt value.Conclusion:TFPI2 can improve the sensitivity of SDC2 methylation–specific detection of colorectal tumorous lesions while maintaining high specificity, in particular reducing the missed detection of left colon cancer and adenoma.