The proinflammatory cytokine, interleukin-6 (IL-6), plays a critical role in many chronic inflammatory diseases, particularly inflammatory bowel disease. To investigate the regulation of IL-6 gene expression at the molecular level, genomic DNA sequencing of Jinghai yellow chickens (Gallus gallus) was performed to detect single-nucleotide polymorphisms (SNPs) in the region −2200 base pairs (bp) upstream to 500 bp downstream of IL-6. Transcription factor binding sites and CpG islands in the IL-6 promoter region were predicted using bioinformatics software. Twenty-eight SNP sites were identified in IL-6. Four of these 28 SNPs, three [−357 (G > A), −447 (C > G), and −663 (A > G)] in the 5′ regulatory region and one in the 3′ non-coding region [3177 (C > T)] are not labelled in GenBank. Bioinformatics analysis revealed 11 SNPs within the promoter region that altered putative transcription factor binding sites. Furthermore, the C-939G mutation in the promoter region may change the number of CpG islands, and SNPs in the 5′ regulatory region may influence IL-6 gene expression by altering transcription factor binding or CpG methylation status. Genetic diversity analysis revealed that the newly discovered A-663G site significantly deviated from Hardy-Weinberg equilibrium. These results provide a basis for further exploration of the promoter function of the IL-6 gene and the relationships of these SNPs to intestinal inflammation resistance in chickens.
Interleukin 6 (IL-6) is an immunoregulatory cytokine involved in various inflammatory and immune responses. To investigate the effects of single nucleotide polymorphisms (SNPs) and haplotypes of IL-6 on resistance to Eimeria tenella (E. tenella), SNPs in the 5′ regulatory region of IL-6 were detected with direct sequencing, and the effects of SNPs and haplotypes on resistance to E. tenella were analyzed by the least square model in Jinghai yellow chickens. Nineteen SNPs were identified in the 5′ regulation region of IL-6, among which three SNPs were newly discovered. The SNP association analysis results showed that nine of the SNPs were significantly associated with E. tenella resistance indexes; the A-483G locus was significantly associated with the GSH-Px, IL-2, and IL-17 indexes (p < 0.05); the C-447G locus was significantly associated with the SOD, GSH-Px, IL-17, and IL-2 indexes (p < 0.05); and the G-357A locus had significant effects on the CAT and IL-16 indexes (p < 0.05). Haplotype analysis showed that H2H3 and H2H5 were favorable haplotype combinations with good coccidium resistance. Furthermore, we used qRT-PCR and observed that the expression of IL-6 in the infection group was higher than that in the control group in the liver, proventriculus, small intestine, thymus, kidney, and bursa of Fabricius and extremely significantly different than that in the cecum especially (p < 0.01). In summary, SNPs and haplotypes in the 5′ regulatory region of IL-6 have important effects on E. tenella resistance, and the results will provide a reference for molecular marker selection of E. tenella resistance in Jinghai yellow chickens.
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