Mechanisms of estrogen-induced effects in avian reproduction caused by transovarian application of a xenoestrogen, diethylstilbestrol

To clarify breeding failure in avian species caused by the estrogenicity of chemicals, alterations in the reproductive systems of Japanese quail exposed in ovo to a xenoestrogen were investigated. An injection of diethylstilbestrol (DES) into the yolk before incubation decreased, after sexual maturation, egg-laying performance of female quails, which accompanied inducing abnormal development of the oviducts. All females treated with 50 ng DES/g of egg did not lay eggs, while 0.5-5 ng DES/g reduced egg weight and eggshell strength and thickness. In the uterus (shell gland), the mRNAs for calcium regulating factors, osteopontin and calbindin D28 K, were reduced dose-dependently by DES. Scanning electron microscopy showed that shell thinning was pronounced in the mammillary and cuticular layers of the eggshell, regions where osteopontin proteins are reportedly located. These indicate that transovarian exposure to xenoestrogens causes malformation and dysfunction of the oviducts, where calcium regulating molecules could play key roles in eggshell thinning.