Methylation, miRNA and gene expression have an integrated sex-specific role in the pineal gland of chickens subjected to unpredictable light schedules

The environment where production animals are reared is fundamental to determine their later health and wellbeing. Stress in production animals generated by common production practices is a frequent issue of concern. In animals undergoing distress, hormonal responses are produced. These include variations in testosterone, epinephrine, prolactin and cortisol. Animals constantly subjected to stress and systemic hormonal changes have their genome and epigenome affected in a variety of cell types. The pineal gland is a region of vertebrate brains that regulates the circadian rhythm of individuals through the secretion of melatonin according to the patterns of light exposure they experience. These mechanisms require gene activation dependent upon light exposures, which strongly suggests the involvement of epigenetic mechanisms. In order to determine whether sustained stressful rearing conditions of chickens can produce long-term epigenomic effects in the pineal gland, we have investigated epigenetic and transcriptomic response in this organ after exposure to unpredictable light patterns. Hy-Line female (n=18) and male (n=16) chickens were randomly divided into two groups after day one after hatching. The control group was kept at standard 12:12 light-dark cycle for their entire life while the chronic light stress group was exposed to an unpredictable light exposure on a randomized schedule with intervals down to 3 hours and up to 21 hours. The pineal gland transcriptomic and miRNA responses to the treatment was carried out by RNA-seq. We found that the pineal gland of male chickens exhibits long-term expression changes after exposure to unpredictable illumination patterns. This effect was not observed in females. Moreover, we identified sex differences in the expression of autosomal genes in the pineal gland. Interestingly, when analyzing the methylome through MeDIP we found that normal sex differences in the pineal gland DNA methylation disappear in the stress group. Light exposure stress produces long-term sex-specific disruption both in methylomic and transcriptomic level in chickens, which could also be of relevance for human health.