Abstract
BackgroundEffect of monochromatic green light illumination on embryo development has been reported in chickens. The avian pineal gland is an important photo-endocrine organ formed by a mediodorsal protrusion during embryonic development. However, the involvement of pineal gland in the light transduction process remains to be elucidated. In the present study, we investigated the influence of monochromatic green light on hatching time and explored the possible mechanism via pineal function.ResultsA total of 600 eggs of White Leghorn (Shaver strain) were incubated under photoperiods of either 12 h of light and 12 h of darkness using monochromatic green light (12L:12D group) or 24 h of darkness (0L:24D group) for 18 d. Compared to 0L:24D group, the green light stimulation shortened the hatching time without extending the hatch window or impairing hatchability. The liver of embryos incubated in the 12L:12D light condition was heavier than those of the 0L:24D group on d 21 post incubation which may be linked to the observed increase in the serum concentration of insulin-like growth factor 1 (IGF-1); primary secretion of the liver. Histological structure analysis of pineal gland demonstrated that the light stimulation increased follicle area, wall thickness and lumen area on d 10 and d 12 post incubation. Rhythmic function analysis demonstrated that three clock related genes (brain and muscle ARNT-like-1, BMAL1; circadian locomotor output cycles kaput, CLOCK; and cryptochrome-1, CRY1) and a melatonin rate-limiting enzyme related gene (arylalkylamine N-acetyltransferase, AANAT) were rhythmically expressed in the pineal gland of the 12L:12D group, but not in the 0L:24D group. Simultaneously, the light stimulation also increased the concentration of melatonin (MT), which was linked to hepatocyte proliferation and IGF-1 secretion in previous studies.ConclusionsThe 12L:12D monochromatic green light stimulation during incubation shortened hatching time without impairing hatching performance. Pineal gland’s early histological development and maturation of its rhythmic function were accelerated by the light stimulation. It may be the key organ in the photo-endocrine axis that regulates embryo development, and the potential mechanism could be through enhanced secretion of MT in the 12L:12D group which promotes the secretion of IGF-1.
Highlights
Effect of monochromatic green light illumination on embryo development has been reported in chickens
Pineal gland’s early histological development and maturation of its rhythmic function were accelerated by the light stimulation. It may be the key organ in the photo-endocrine axis that regulates embryo development, and the potential mechanism could be through enhanced secretion of MT in the 12L:12D group which promotes the secretion of insulin-like growth factor 1 (IGF-1)
The results indicate that the light treatment had no effect on the weight of embryo (Fig. 2a), heart (Fig. 2c) or pectoral muscle (Fig. 2d) from d 17 to 21 post incubartion (P > 0.05)
Summary
Effect of monochromatic green light illumination on embryo development has been reported in chickens. We investigated the influence of monochromatic green light on hatching time and explored the possible mechanism via pineal function. Avian species have a broader visible light spectrum [1, 2] and special extra-retinal photoreceptor in pineal gland [2, 3]. They are more sensitive to environmental lighting than mammals. Monochromatic green light was shown to promote the growth of spleen [6] and skeletal muscle [7] in broilers. The stimulating effect of monochromatic green light on skeletal muscle was linked to enhanced circulation levels of insulin-like growth factor 1 (IGF-1) in blood [7, 10, 11]. IGF-1 may play an important role in the lightmediated advanced development of chick embryo
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