Abstract
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.
Highlights
Interleukin-6 (IL-6), known as interferon β-2, stem cell-stimulating factor, or B cell differentiation factor, is a multifunctional cytokine that plays an important role in regulating the immune response, acute-phase response, and haematopoiesis in chickens [1]
A total of 28 single-nucleotide polymorphisms (SNPs) sites were detected (Table 2), among which 19 SNPs are located in the 50 regulatory region, and three were newly discovered; the chromosomal positions of these three SNPs are 30948722, 30948938, and 30949028
To determine the effect of these SNPs on changes of the predicted CpG island in the promoter region of IL-6, MethPrimer software was used to predict the presence of CpG islands in the 2200-bp sequence upstream of the transcription start site of the IL-6 promoter region before and after SNP site mutations
Summary
Interleukin-6 (IL-6), known as interferon β-2, stem cell-stimulating factor, or B cell differentiation factor, is a multifunctional cytokine that plays an important role in regulating the immune response, acute-phase response, and haematopoiesis in chickens [1]. Amrani et al [2]. First discovered that chicken IL-6 influences hepatocyte-stimulating factor (HSF) in the acute-phase response. Schneider et al [3] successfully cloned the complete reading frame cDNA for chicken IL-6. Horiuchi et al [4] reported that the chicken leukaemia inhibitory factor belongs to the IL-6 family. By injecting DNA plasmids carrying the very virulent infectious bursal disease virus (vvIBDV) SH95 poly-protein (VP2-4-3) gene and DNA plasmids carrying chicken IL-6 (ChIL-6), Sun et al [5] determined that injection with ChIL-6 plasmids resulted in a significantly increased protective effect in chickens after infection with highly virulent strains. IL-6 plays a vital role in the chronic inflammation and
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