Differentiation of chicken gonad as an endocrine organ: expression of LH receptor, FSH receptor, cytochrome P450c17 and aromatase genes

The gonad is an endocrine organ secreting sex hormones and also a target of pituitary gonadotrophins. The expression of mRNAs encoding LH receptor (LHR), FSH receptor (FSHR), P450c17 and P450aromatase in the developing gonads of embryos between day 4 and day 6 of incubation was determined using a RT-PCR to elucidate the chicken gonad as a target organ of gonadotrophins. Although expression of mRNAs encoding LHR, FSHR and P450c17 was detected at day 4 of incubation in both sexes, mRNA encoding P450aromatase appeared at day 6 in female embryos only, indicating that mRNAs encoding gonadotrophin receptors can be identified before sexual differentiation. Quantitative PCR analysis revealed that expression of mRNA encoding LHR and FSHR remained low in male gonads from day 4 to day 6 of incubation, whereas they increased on day 6 in female gonads. The sexual dimorphism in the expression of mRNAs encoding LHR and FSHR was confirmed in the sexually differentiated gonads of embryos at day 12 of incubation (LHR in ovary ratio LHR in testis = 7 ratio 1; FSHR in ovary ratio FSHR in testis = 9 ratio 1).