Differential expression of dmrt1 and ovarian aromatase during sex differentiation period in pejerrey, Odontesthes bonariensis.

JUAN IGNACIO FERNANDINO; RICARDO HATTORI; PABLO STROBL MAZZULLA; CARLOS AUGUSTO STRÜSSMANN; GUSTAVO M SOMOZA

Saint Malo. Francia

Congreso; 8th International Symposium on Reproductive Physiology of Fish.; 2007

BACKGROUND: The process of sex determination in teleosts can be controlled by genetic and/or environmental factors. Our experimental model, the pejerrey, is a gonochoristic inland water fish with a very strong temperature sex determination (TSD) system. The proportion of females decreases gradually from 100% at 19°C to 50% around 23-25°C and 0% at 29°C. Dmrt1 is a transcription factor playing an important role in male sex differentiation in vertebrates. On the other hand, the ovarian form of cytochrome P450 aromatase (cyp19A1), the enzyme that catalyzes the conversion of androgens to estrogens, has been implicated in female sex differentiation in TSD reptiles, amphibians, and fish. However, the simultaneous expression of both genes during the period of sex determination/differentiation has been poorly studied in fish.   METHODS: Larvae were stocked in three 200-l tanks and kept at 17°C (feminizing), 25°C (mixed-sex producing) and 29°C ± 0.5°C (masculinizing temperature). Larvae (n=5 at 17 and 29°C, n=10 at 25°C) were sampled weekly from hatching to week 8. The expression profiles of dmrt1 and cyp19A1 were determined by Real Time PCR during the sex determination/differentiation period.   RESULTS: The abundance of dmrt1 mRNA showed significant differences among larvae maintained at 17°C and 29°C. Its expression significantly increased after week 4 at 29°C, remaining low throughout the study at 17°C. On the other hand, cyp19A1 expression increased from week 6 at 17°C but remained at low levels at 29°C. Both differences were observed before histological sex differentiation of the gonads (week 7 and 6 for females at 17°C and 25°C, respectively, and week 7 and 6 for males at 25°C and 29°C, respectively). The expression levels of both genes at the mixed-sex producing temperature were bimodal, showing similar values to those at either feminizing or masculinizing temperatures.   CONCLUSION: Dmrt1 and cyp19A1 genes showed differential expression during the sex differentiation period at feminizing, mixed-sex producing and masculinizing, temperatures. The expression patterns of the two genes support the idea that both are involved in the process of sex differentiation in this species.   Supported by C.A.S. (Ministry of Education, Culture, Sports, Science and Technology of Japan #15201003) and G.M.S. (PICT#01-12168 from Agencia Nacional de Promoción Científica y Tecnológica, ANPCYT, Argentina) grants.