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Prenatal light exposure affects diurnal rhythms and visual development of the layer embryonic retina
1Department of Agricultural Structure and Environmental Engineering, College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China.
Insights
Prenatal light exposure influences chicken embryo development. White light (WL) promoted retina development and circadian rhythm establishment compared to green light (GL) or no light (NL).
Area of Science:
- Developmental biology
- Neuroscience
- Chronobiology
Background:
- Prenatal light exposure is hypothesized to influence avian embryonic development and circadian rhythm establishment.
- Understanding the impact of light wavelengths on embryonic development is crucial for poultry science.
Purpose of the Study:
- To investigate the effects of prenatal white light (WL) and green light (GL) exposure on chicken embryonic retinal morphology, visual signaling pathways (TGF-β/Smad), clock gene expression, and melatonin levels.
- To determine how different light wavelengths during incubation affect the establishment of diurnal rhythms in the embryonic retina.
Main Methods:
- Chicken eggs were incubated under white light (WL), green light (GL), or no light (NL) with a 12L:12D photoperiod.
- Retinal morphology, TGF-β/Smad pathway gene/protein expression, clock gene (cClock, cBmal1, cBmal2, cAanat) expression, and melatonin concentration were analyzed at embryonic day 20 (E20).
- Diurnal rhythmicity of gene expression and melatonin was assessed.
Main Results:
- WL incubation resulted in thicker retinas and retinal laminae compared to GL at E20.
- WL significantly downregulated TGF-β1 mRNA and Smad2/3 protein expression compared to NL and GL.
- GL incubation promoted diurnal rhythms in clock genes (cBmal1/2, cClock) and cAanat, and enhanced melatonin secretion without diurnal rhythm.
- WL incubation established diurnal rhythms in cBmal1, cAanat, and melatonin, while NL only showed rhythmicity in cBmal1.
Conclusions:
- Prenatal light exposure, particularly white light, significantly influences embryonic retinal development and the establishment of circadian rhythms in chickens.
- White light appears advantageous for retina development and diurnal rhythm establishment by modulating visual signaling and clock gene expression.
- A well-developed retina under WL may facilitate melatonin rhythm establishment, potentially benefiting overall embryonic development.
Abstract:
It is believed that some wavelengths of light penetrate through eggshell and are perceived by avian embryo, and may consequently affect rhythm establishment and development. This research aimed to explore the influence of prenatal light exposure on the morphological alterations of retinal tissue, the expression of visual developmental signaling systems (TGF-β/Smad pathway), the expression of clock related genes (cClock, cBmal1, cBmal2, cAanat), and melatonin concentration in the chicken embryonic retina. Layer eggs (Jingfen No.6) were subjected to white light (5000K, WL) and green light (520 nm/515-525 nm, GL) with a 12L:12D photoperiod throughout the entire incubation period, in contrast to no light incubation (NL). The results showed that the thickness of retina and each retinal lamina of chicken embryo in WL at E20 was much thicker than that of chicken embryo in GL (P < 0.05). In contrary, the expression level of TGF-β1 mRNA and Smad2/3 protein in retina was dramatically downregulated in WL when compared to that in NL and GL (P < 0.01). Furthermore, the incubation light simultaneously significantly affected the diurnal rhythms of the chicken embryonic retina. The expression of three clock genes (cBmal1/2, cClock) and cAanat exhibited significant diurnal rhythms in GL (P < 0.05). Additionally, green light stimulation significantly enhanced melatonin secretion but did not show diurnal rhythm. However, cBmal1, cAanat, and melatonin expression exhibited diurnal rhythms (P < 0.01), while the others did not in WL. In NL, only cBmal1 exhibited diurnal rhythmicity (P < 0.01). In conclusion, providing light of different wavelengths during the incubation process of poultry can have varying effects on embryonic visual development and the establishment of diurnal rhythms. WL had an advantage to GL and NL on retina development and diurnal rhythm through significantly influencing the expression of genes related to visual developmental signaling pathways and clock genes. A well-developed retina in WL exposure chicken embryo may be beneficial for establishing a melatonin rhythm. Conversely, the established circadian rhythm could improve embryonic development.
