Fresh insights into the light‐induced pineal gland circadian rhythm transmission mechanism derived from mRNA and miRNA profiling

Abstract

The circadian clock significantly impacts animal health and productivity, with light playing a crucial role in regulating circadian rhythms. However, the mechanisms behind light‐induced circadian transmission remain unclear, particularly in light‐sensitive avian species. The pineal gland is a key component acting as the photosensitive master oscillator in the avian clock system. Using transcriptome sequencing and small RNA sequencing technologies, we identified circadian genes and miRNAs in the chick pineal gland under light–dark and sudden constant‐light conditions. We observed rhythmic oscillations in up to 1299 genes during the light–dark cycle, with 400 genes maintaining rhythms under constant light. Our findings highlight the light‐sensitive temporal organization in birds as the phase distribution of circadian genes in the pineal gland correlates with light exposure changes. A novel regulatory mechanism involving light, cyclic adenosine monophosphate, cyclic guanosine monophosphate, light‐sensitive miRNAs, such as gga‐miR‐34b‐5p, and light‐sensitive circadian genes, such as CRY2, was discovered to participate in the light input system of the chick pineal clock, through which light regulates the oscillators and outputs of the circadian clock system. Additionally, transcriptomic analysis, liquid chromatography–mass spectrometry, and Oil Red O staining revealed cyclic changes in lipid synthesis and metabolism throughout the circadian day, which may be a key mechanism through which the circadian clock influences pineal physiology. Our results enhance the understanding of light‐induced circadian transmission mechanisms and identify potential targets for optimizing the circadian clock through light.