Green tea extract disrupts gonadal differentiation in a model avian system

In the poultry industry, green tea extract (GTE) is becoming an increasingly popular dietary supplement due to its observed beneficial effects on performance and egg quality. However, work in mammals indicates that the active ingredients in green tea extract, catechins, act as endocrine disruptors, interfering with the actions of estrogen. Given that GTE is often supplemented to hens during egg-laying, there is potential for the endocrine-disrupting properties of catechins to interfere with the sensitive process of sexual differentiation in embryos. We tested whether green tea extract (GTE) alters gonadal differentiation in Japanese quail (Coturnix japonica) embryos. We injected eggs with either GTE or a Control vehicle before the onset of differentiation on the 4th day of incubation. On day 15, we evaluated phenotypic sex (gonadal morphology) and genetic sex (via PCR). Embryos from eggs that were injected with GTE had increased genotype-phenotype mismatches, which occurred exclusively in genetic females (ZW) who developed bilateral gonads resembling testes. Among genetic females, GTE significantly increased the probability of a male phenotype. Treatment with GTE did not increase embryonic mortality compared to Controls. We conclude that GTE modifies the developmental trajectory of embryonic gonads, specifically for female embryos. We propose that GTE disrupts the critical estrogen-dependent window of female sex differentiation, leading to sex reversal.