Feminizing Turtle Embryos as a Conservation Tool

Many data suggest an involvement of estrogens in gonadal differentiation in reptiles with temperature-dependent sex determination (TSD). However, the site of estrogen synthesis in two species of freshwater turtles is unclear. In Emys orbicularis, estrogens were shown to be produced by the gonads, whereas in Trachemys scripta, gonadal steroids were not detected. The marine turtle Dermochelys coriacea exhibits TSD but in gonadal development, ovarian differentiation is delayed. Gonadal aromatase activity and estrogen content in this species were measured in embryos incubated at 27 degrees and in embryos incubated at 30.5 degrees, respectively, masculinizing and feminizing temperatures within the range of temperatures found in natural nests. At all stages studied, aromatase activity was present and found to be higher at 30.5 degrees than at 27 degrees. Estrogens were only found at 30.5 degrees. The effects of temperature shifts on gonadal aromatase activity were then examined. Eggs were shifted from 27 to 35 degrees (feminizing temperature) at different embryonic stages and exposed to 35 degrees for 6 days. An increase in gonadal aromatase activity, although with significant individual variations, was seen only when eggs were shifted between stages 23 and 27. These stages are in the range of the thermosensitive stages for sexual differentiation of the gonads determined in other turtles. These results are similar to those previously obtained in E. orbicularis and agree with a key role for endogenous estrogens in gonadal differentiation of reptiles with TSD.(ABSTRACT TRUNCATED AT 250 WORDS)

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.