DNA methylation of pituitary growth hormone is involved in male growth superiority of Nile tilapia (Oreochromis niloticus).

Growth hormone (GH) and its receptors are critical regulators of somatic growth and metabolism. It has been shown in mammals that the methylation of cytosines within the GH promoter plays a key role in regulating transcripts expression. In the present study, the GH, GHR1 and GHR2 proximal promoters were identified and the methylation levels of these genes in corresponding tissues were assayed. The results suggested that significant arising of GH putative promoter methylation levels in pituitary was observed in females compared with males. However, no such sex-specific changes were found in GHR1 and GHR2 promoters. The GH mRNA expression also was influenced by GH promoter methylation levels in pituitary, which resulted in the higher growth rate of Nile tilapia males. Meanwhile, the methylation levels of GH putative promoter were negatively correlated with growth rate as well as mRNA expression of GH. Furthermore, the methylation of specific E-Box CpG site is also negatively related to the mRNA expression of GH in pituitary. Taken together, our data provide an epigenetic mechanism of explicating the sex duality in phenotypic plasticity of growth rate in male and female of Nile tilapia.