Effect of Exogenous Estrogen Treatment on the Gonadal Estrogen Receptor-ɑ Expression in Male Chickens (Gallus domesticus)

Abstract

Sexual differentiation in chickens is controlled by both direct genetic and hormonal mechanisms which can cause genetic sex reversal though manipulations. Estrogen is critical for normal ovarian development and in-ovo estrogen treatment, can feminize genetically male (ZZ) chicken gonads temporarily although a permanent sex reversal could be observed by blocking the Estrogen synthesis in genetic females. The reason for this temporary nature of male to female sex reversal is still unknown. Although in-ovo estrogen treatment triggered the Estrogen Receptor-α (ER-α ) expression in embryonic gonads, the post hatching gonadal expression of ER α with age which can possibly affect the temporary nature of this phenomenon has not been studied adequately. Therefore, the aim of the current study was to investigate the post-hatching ER-α expression in left gonads when the exogenous estradiol supply is continuous. Commercial Shaver brown chicken eggs were incubated under standard conditions by giving two in-ovo injections, 0.1mg/egg Estradiol Cypionate and same volume of sterile Phosphate Buffered Saline to the treatment and control eggs, respectively. The genetic sexing was done using W chromosome specific sex marker HUR0424. A half of treated male chicks were given with a weekly post-hatching injection of 0.1mg/chick Estradiol Cypionate intra-muscularly (T2) and the rest was raised with no post-hatching injection (T1). Three chicks from each group, including control (C) were sacrificed at 1, 4 and 8 weeks intervals. Total RNA was extracted from the left gonads using the TRIzol method followed by reverse transcription of ER-α gene using a pair of gene specific primers. Following the PCR amplification, the relative quantification of the ER-α expression was performed relative to the expression of reference gene Glyceraldehyde-3- Phosphate Dehydrogenase. Data were analyzed using (SAS) version 9.0. The expression of ER-α showed a significant increase with the age (P<0.0001) and difference among treatments (P<0.0001) where the highest expression was observed at T2 followed by T1. However there was no significant interaction effect observed (P=0.1203) among the groups. Accordingly it can be suggested that although the ER-α expression was induced by exogenous estradiol, there is a male specific mechanism to decrease the triggered ER-α expression, with age.