Immediate and delayed hypothalamic response to monochromatic green illumination during the avian embryonic period are mediated thorough epigenetic modulations
In this study, we investigated the effects of light-induced fetal responses in avian species, specifically focusing on green monochromatic illumination (GMI). Broiler eggs were exposed to GMI either throughout the entire incubation period (Green) or specifically during the final three days before hatching (G3D), with control groups incubated in dark or white light conditions. Unbiased genome-wide analyses at day of hatch (DOH) revealed significant transcriptional changes in the hypothalamus of the G3D group, highlighting over 500 differentially expressed genes. In parallel with these transcriptional changes, our epigenetic analysis revealed that GMI exposure in the G3D group resulted in increased binding of phosphorylated CREB1 (pCREB1) and elevated levels of Histone H3 Lysine 27 acetylation (H3K27ac) at gene promoters linked to growth, appetite, and metabolism. Mechanistically, we found that pre-exposure to blue light, which disrupts green photoreceptor activity, reduced retinal green opsin levels and nullified the epigenetic modifications typically induced by GMI in the G3D group. Phenotypically, the G3D group exhibited increased post-hatch body weight at several stages, suggesting enhanced growth plasticity and metabolic efficiency, though these effects diminished with age. This study underscores the significant role of specific wavelengths and timing of light exposure in shaping developmental trajectories, and highlight the crucial role of epigenetics in shaping organismal responses to their environment. Overall design: broiler hypothalami from day of hatch incubated in 4 diffrenet illumination regimes: dark incubation (control), white illumination (white), green illumination throught the entire incubation (green) and green illumination only at the last three days of incubation (g3d)