Brain aromatase expression, activity and immunohistological analysis during termolabile sex determination/differentiation period in pejerrey fish. Differences in brain cell proliferation.

PABLO STROBL MAZZULLA; JUAN IGNACIO FERNANDINO; LEONARDO GASTÓN GUILGUR; ANALÍA NUÑEZ; CARLOS; ELIZABETH PELLEGRINI; OLIVIER KAH; GUSTAVO MANUEL SOMOZA

Saint Malo, France

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

BACKGROUND: In pejerrey gonadal sex is strongly determined by temperature (all males and all females are produced at 29ºC and 17ºC, respectively). In this species, as in other non-mammalian vertebrates, estradiol plays an important role in ovarian differentiation. Also, estradiol is very important in brain development and sexual differentiation of the dimorphic brain areas in mammals, but little is known on the role of estrogens in the development of fish brain. In this context, the objective of this work was to investigate the expression and activity of brain aromatase during the period of temperature sex determination/differentiation and also the differences in brain cell proliferation in fish raised at masculinizing and feminizing temperatures   METHODS: Brain aromatase expression was measured weekly by quantitative RT-PCR on total RNA extracted from the head of larvae reared at feminizing and masculinizing temperatures during the temperature-sensitive window (0-5 weeks) and the gonadal differentiation period (5-13 weeks). Aromatase activity in the head was also measured using the tritiated water assay. Brain and pituitary gland aromatase ontogeny was analyzed by inmmunohistochemistry. Brain cell proliferation was analyzed by immunocytochemistry during early termolabile sex determination period on brain slices of fish exposed for a short time to bromodeoxyuridine (BrdU). These brains were also analyzed using immunofluorescense against PCNA.   RESULTS: Brain aromatase expression was significantly higher at the masculinizing temperature during the sex determination and gonadal differentiation periods. A similar trend was observed when aromatase activity was analyzed in fish heads. Larvae at the masculinizing temperature exhibited higher aromatase activity at 5-6 weeks, just previous to the gonadal sex differentiation period. Aromatase-positive cells were firstly evidenced in the pituitary gland (2-3 weeks) and then in cells lining the ventricles (4 week), as observed in adults, without clear differences between temperature treatments. There was a clear sex/temperature-related difference in cell proliferation during the fourth week, where larvae maintained at feminizing temperature exhibited a clearly higher brain cell proliferation than those at the masculinizing temperature. A large majority of the new-born cells were observed in periventricular areas.   CONCLUSION: These results suggest that temperature exerts a strong effect on brain aromatase expression and that estradiol may be required for the masculinization of larval brain. Our findings also indicated the likely existence of a sex-specific mechanism modulating neurogenesis during this period and the possibility that it participates in the construction of sexually dimorphic brain circuitry.