Expression pattern of estrogen receptors and vitellogenin in genistein fed male and female common carp brooders
Estradiol signalling is stimulated or inhibited depending upon the interaction mechanism of estrogen receptors, ERα and ERβ. Soy-phytoestrogens, especially genistein, is known to bind these receptors and affect vitellogenin (vtg) synthesis. Fifty-six days of feeding trial was conducted to evaluate the effect of genistein on ERα, ERβ and vtg gene expression in male and female brooders of Cyprinus carpio. Five groups of fishes were fed with 0 (C), 1 (G-1), 3 (G-3), 6 (G-6) and 9 (G-9) mg% genistein contained feed during the trial. mRNA concentrations in liver tissue were determined by relative analysis using realtime PCR. The study observed a significant vtg mRNA level reduction from G-6 in female and a significant induction in male fishes after G-6. Expression of ERα gene was showed an increasing trend up to G-6 in while ERβ gene expression was reduced with increasing dose of genistein in female fishes. Higher ERα mRNA level was observed in G-3 and G-6 in male fishes, while ERβ mRNA level was comparatively lower in male and showed no significant difference between the treatment groups. The study revealed that both ERα and ERβ are sensitive to dietary genistein in female brood fishes than male. Genistein at 6mg%, so as soybean meal at 27% inclusion (considering genistein content of defatted soybean meal is 22.50±1.09 mg/100g) disrupts the estradiol cascade pathway by reducing the expression of ERβ gene and vitellogenin synthesis in a female brooder of C. carpio. Genistein induces vitellogenin synthesis at 6mg% by inducing ERα gene expression in the liver of male brooder. Hence the investigation concludes that though the practice of soybean meal in aquafeed is inevitable; however, its inclusion in a brood-stock diet needs serious attention.