Genome-wide DNA methylation and transcriptome analyses reveal important epigenetic genes associated with valgus-varus deformity in broilers

1. Valgus-varus deformity (VVD) is a common leg bone problem in broilers that causes serious economic losses to the breeding industry. The genetic aetiology of VVD is not clear, which restricts the genetic control of VVD. 2. In this study, knee cartilage of 35-day-old VVD and normal broilers was sequenced by whole-genome bisulphite sequencing (WGBS). The unique whole-genome DNA methylation profile of VVD broilers was described, and the methylation data and transcription data were used for joint analysis. 3. The mean methylation level of the VVD group was greater than that in the normal group. A total of 4315 differentially methylated regions (DMRs) were detected from methylation data, with the highest DMR density on chromosomes 25, 27, 31 and 33. DMRs were mainly located in introns, which accounted for more than 60%, followed by promoter and exon regions. 4. A total of 2326 differentially methylated genes (DMGs) were identified from DMRs, including 1159 genes with upregulated DMRs, 936 genes with downregulated DMRs, and 231 genes with two types of DMRs. 5. The <i>ESPL1</i> gene may be an important epigenetic gene of VVD. The methylation of particular CpG17, CpG18 and CpG19 sites in the promoter region of the <i>ESPL1</i> gene may hinder the binding of transcription factors and promoters and increase the expression of <i>ESPL1</i>.