Quantification of Aromatase and 5α-Reductase During Gonadal Development in Trachemys scripta, a Reptile with Temperature-Dependent Sex Determination
McQuade, Ryan S.
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In many reptiles, the incubation temperature of the egg determines the sex of the offspring. The red-eared slider turtle, Trachemys scripta, shows such a pattern of sex determination, known as temperature-dependent sex determination (TSD). At temperatures below 28.6° C all male hatchlings are produced, while above 29.5° C all female hatchlings are produced; in the intermediate range a mixed sex ratio is observed. Previous research has supported the hypothesis that temperature effects sex determination by activating genes which code for enzymes in hormone metabolism, which through their action alter the hormone microenvironment of the embryo. The enzymes aromatase and 5α-reductase, which convert testosterone to estradiol and dihydrotestosterone, respectively, have been shown to be important in TSD. Administration of chemicals which inhibit these enzymes during the temperature-sensitive window of embryonic development leads to sex reversal in the offspring. Inhibition of aromatase creates a male phenotype at female-producing temperatures, while inhibition of 5α-reductase creates a female phenotype at male-producing temperatures. The relative amounts of these enzymes in embryonic gonadal tissue from different incubation temperatures before, during, and after sex determination are being assayed by incubating tissue homogenate with 3 H- testosterone and isolating the radioactive products using both TLC and HPLC.