The yellow-toothed-cavy (Galea spixii) is a species of rodent of the subfamily Caviinae and family Caviidae, that living in Caatinga vegetation of the Brazilian Northeast. The characteristics of the females of this species, such as Cavia porcellus is the presence of a vaginal closure membrane and a hypertrophied clitoris trespassed by the urethra, which opens at its top, giving a characteristic of a pseudo-penis, which can be related to an androgenization in utero at time of sexual differentiation of embryos,as seen in other studies with female moles, primates, carnivores and humans, which show that females where can be observed androgenization and virilization of the genitalia, are noted intrauterine hormonal changes related with enzymes that produce sex steroid hormones in the adrenal gland, gonads and placenta, which may expose the female embryo to high androgen levels during sexual differentiation. Therefore, the present research aims to describe morphologically the events of sexual differentiation in the embryo 10, 15, 20, 25, 30, 35, 40 and 45-48 days of gestation, as well as evaluate the immunolocalization, molecular characteristics and expression levels variation from STAR protein and enzymes: cytochrome P450c17, 17-²-HSD and 3-²-HSD in adrenal and gonads of male and female embryo/fetuses and placenta. It will also be measured the expression of anti-Müllerian hormone, 5-alpha reductase enzyme and androgen receptors in the testes and ovaries and expression of cytochrome P450 aromatase in the ovaries of Galea spixii at different gestational periods,attempt to understand its relationship with the virilization mechanisms of the external genitalia with the channeling of the clitoris by urethra in the females and the phenomenon of the vaginal closure membrane formation and the formation of other genital organs from male and female after sexual differentiation in this rodent species, which has great ecological and economic importance to national fauna.
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