DNA methylation and expression of proopiomelanocortin (POMC) gene in the hypothalamus of three-week-old chickens show sex-specific differences

Abstract

Increased availability and improved sequence annotation of the chicken (Gallus gallus f. domestica) genome have sparked interest in the bird as a model system to investigate translational embryonic development and health/disease outcomes. However, the epigenetics of this bird genome remain unclear. The aim of this study was to determine the levels of gene expression and DNA methylation at the proopiomelanocortin (POMC) gene in the hypothalamus of 3-week-old chickens. POMC is a key player in the control of the stress response, food intake, and metabolism. DNA methylation of the promoter, CpG island, and gene body regions of POMC were measured. Our data illustrate the pattern, variability, and functionality of DNA methylation for POMC expression in the chicken. Our findings show correlation of methylation pattern and gene expression along with sex-specific differences in POMC. Overall, these novel data highlight the promising potential of the chicken as a model and also the need for breeders and researchers to consider sex ratios in their studies.

Keywords: DNA methylation; chicken; epigenetics; hypothalamus; proopiomelanocortin; sex specific.

Figure 1

Chicken POMC locus and DNA methylation analyses. (A) Schematic representation of the sequencing map for the POMC gene region including CpG islands, promoter, and gene body chromosomal locations of pyrosequencing assays. (B) Corresponding DNA methylation levels at individual CpG sites across the target regions in 3‐week‐old juvenile chickens (Gallus gallus f. domestica). n = 21.

Figure 2

Hypothalamic POMC DNA methylation and gene expression according to sex and correlation analysis in 3‐week‐old chickens. (A) Schematic representation of the POMC promoter region pyrosequencing assays. (B) Sex‐specific differences for DNA methylation levels at POMC promoter region CpG sites Pos.3 PromS1 and Pos.5 PromS2. F, females; M, males. (C) Hypothalamic POMC mRNA expression according to sex. (D) Statistically significant relation between DNA methylation level at promoter CpG site, Pos.5 PromS2, and mRNA expression of POMC. n = 21.