Effects of light on development of mammalian zygotes

Abstract

It is generally assumed that light has no effect on the physiology of oocytes, zygotes, or early embryos. Therefore, little or no attention has been paid to lighting conditions during the handling of these cells in vitro. Here we show that cool white fluorescent light, rich in short-wavelength visible light and commonly used in research and clinical laboratories, produces more reactive oxygen species in mouse and hamster zygotes than does warm white fluorescent light. Mouse blastocysts that developed from zygotes shielded from light best developed to term fetuses followed by those exposed to warm white fluorescent light and then by those exposed to cool white fluorescent light. We hypothesized that light is one of the physical factors affecting embryonic environment and that its effects on cultured mammalian zygotes and embryos should not be overlooked.

Fig. 1.

Production of ROS in hamster and mouse zygotes after 15-min exposure to fluorescent light (1,200 lx). The level of hydrogen peroxide is expressed as the relative fluorescein intensity of 6-carboxy-2′,7′-dichlorodihydrofluorescein diacetate di(acetoxymethyl ester). Each column shows the mean ± SEM. *, P < 0.05; **, P < 0.001; one-way ANOVA and Bonferroni's multiple comparison test (10 zygotes for each group in hamster and 6 zygotes for each group in mouse were analyzed).

Fig. 2.

Incidence of apoptotic cells in mouse blastocysts after exposure of zygotes to sunlight (>20,000 lx) and cool white and warm white fluorescent light (1,200 lx). Control zygotes were shielded from light by wrapping the dishes with aluminum foil. Zygotes were cultured in KSOMaa with 1 mg/ml albumin until they became blastocysts. The incidence of apoptosis in blastocyst developed in vivo throughout is indicated by a thick arrow. Each point represents the mean of 30 determinations from three replications. All error bars represent the S.E.M. *, P < 0.001 versus the development of all in vitro groups; **, P < 0.01 versus cool white fluorescent light exposure for 15 min; one-way ANOVA and Dunnett's test.

Fig. 3.

Apoptotic cells in mouse blastocysts. (A) Blastocyst developed from a zygote exposed to cool white fluorescent light (1,200 lx) for 15 min. Note the many fragmented, apoptotic cell nuclei shown by TUNEL assay (yellow). (B) Blastocyst developed from a zygote not exposed to light. (Scale bars: 30 μm.)

Fig. 4.

Spectral distribution of cool white and warm white fluorescent lamps (quoted Panasonic technical data).

Fig. 5.

A simple incubator used during light exposure of zygotes. Dishes with zygotes were put on a heated plate (37°C) covered with a transparent plastic hood (clear polystyrene, 1 mm in thickness at the hood top) through which a mixed gas (5% CO₂/5% O₂/90% N₂) was constantly passed. The left dish was a control covered with aluminum foil. (A) Top view. (B) Side view. (Scale bars: 1 cm.)