AROMATASE-ACTIVITY IN GONADS OF TURTLE EMBRYOS AS A FUNCTION OF THE INCUBATION-TEMPERATURE OF EGGS

In embryos of the European pond turtle, sexual differentiation of gonads is temperature-dependent. Production of oestrogens appears to play a key role in this phenomenon. Gonadal aromatase activity was measured in embryos incubated at 25-degrees-C (masculinizing temperature) and at 30-degrees-C (feminizing temperature). At the beginning of the thermosensitive period, the aromatase activity was low at both temperatures but was somewhat higher at 30 than at 25-degrees-C. Afterwards, it remained low in differentiating testes at 25-degrees-C, whereas it increased in differentiating ovaries at 30-degrees-C to form a marked peak when germ cells underwent meiotic prophase. Eggs were shifted either from 25 to 30-degrees-C (highly feminizing) or from 30 to 35-degrees-C for 6 days at different stages of embryonic development. The 25-35-degrees-C shifts performed during the thermosensitive period strongly increased the aromatase activity but were ineffective after this period. The 30-35-degrees-C shifts increased the aromatase activity at all stages. Altogether, results indicate that, in differentiating gonads of turtle embryos, temperature acts on the regulation of synthesis (and therefore activity) of cytochrome P-450 aromatase (P-450-aro). The expression of the P-450-aro gene itself could be temperature-dependent. However, temperature could also act upon the expression of another gene involved in P-450-aro regulation.