Investigação de mecanismos da determinação e da diferenciação sexual dependente de temperatura em zebrafish (Danio rerio) e em duas espécies de tartarugas marinhas (Caretta caretta e Eretmochelys imbricata)

Abstract

Mechanisms of sexual determination vary greatly among vertebrates. Sea turtles show temperature dependent sex determination with a thermosensitive period during egg incubation in which the gonad differentiation occurs. Like turtles, some fish also are temperature sensitive. Zebrafish (Danio rerio) is an animal model used in several areas of biomedical research that, despite its widespread use, whose sexual differentiation conditions and mechanisms are not fully elucidated. In addition to temperature, genetic and environmental factors may also play a role in the sexual differentiation of these species. This dissertation had two parts. In the first, the techniques for investigating the sex-dependent mechanism of sexual determination in zebrafish were standardized. Our results demonstrate that zebrafish first undergoes a stage of juvenile hermaphroditism prior to sexual differentiation. Exposure to controlled temperatures (24 ° C, 26 ° C, 28 ° C or 30 °C) during the initial developmental period starting at 4 hours post fertilization (hpf) significantly influenced hatching and survival rates over the first 7 days post- fertilization (dpf). Embryonic heart rate at 24 and 48 hours post-fertilization were also impacted. Histological analyzes of the gonads demonstrated that different temperatures evaluated may delay or accelerate the process of sexual development during the initial phase compared to animals kept at 28°C. Analysis of the sex ratio has shown that intermediate temperatures (26 and 28 ° C) may favor the development of more males. The second part of this study aimed to investigate aspects of the sexual development of two species of sea turtles (Caretta caretta and Eretmochelys imbricata) in order to contribute to the understanding of the mechanisms of sexual determination and differentiation and the establishment of methods that allow the sexing of the same in phases of development in a more practical and less invasive way than those currently used. Sea turtles born to cubs already have the defined sex, having a different degree of development between the species Caretta caretta and Eretmochelys imbricata, probably due to the shorter incubation time of C.caretta. With the standardization of ELISA techniques, it has been shown that kits for the evaluation of human sex hormones can be used to quantify hormones for both zebrafish and sea turtles. Analysis of the expression of genes involved in the process of sexual differentiation is under way.