Aspectos moleculares da diferenciação sexual em tambaqui (Colossoma macropomum): identificação de vias não convencionais em uma espécie neotropical

Abstract

Fish exhibit a wide variety of mechanisms of sex determination and sexual differentiation, which are topics of great scientific interest and also relevant to the fish industry, specifically when the exploitation of one sex is more advantageous in species of economic importance. The tambaqui Colossoma macropomum is a prominent neotropical species in Brazilian aquaculture. Still, the mechanism of sex determination of tambaqui has not yet been properly identified and characterized, despite efforts using omic technologies such as sequencing the genome of males and females, and also juvenile transcriptomes during the sexually undifferentiated phase. Seeking to expand the scientific knowledge about the mechanisms involved in the tambaqui sexual differentiation process, this thesis had as main objective to identify and evaluate, by in silico and in vivo analyses, the molecular mechanisms involved in this process, mainly those related to steroid hormones and their precursors as well as fatty acids. In the Chapter 1, we show that fish diversity is not restricted to the top of the sex-determining cascade, but also to the different genetic, hormonal and molecular pathways necessary for the development of reproductive organs and the behavior of males and females of the species. Unexpected results about the expression of genes involved in the production of estradiol, such as cyp19a1a and cyp19a1b, and estradiol receptors, which have been recently reported in fish of the order Characiformes, indicate that estradiol possibly has a different role in this lineage, compared to classically established in the literature. Our results from chapter 2 suggest that the substantial variations in the function of gonadal and brain aromatase in tambaqui may be a consequence of the drastic changes in the cis and trans-regulatory region resulted from the rearrangements evidenced in the genomic sequence where these genes are located, when compared to species phylogenetically more distant species such as zebrafish, tilapia, medaka and arowana. Furthermore, the gene expression analysis of aromatase cyp19a1a and cyp19a1b during sexual differentiation and in adulthood, together with the unexpected lack of effect of endocrine disruptors on tambaqui sex ratio, reinforce that estradiol may have a less critical role in the ovarian development or it might be fundamental for the development and maintenance of the gonads in both sexes of this species. In chapter 3, the remarkable differential expression of genes belonging to the elovl family, more expressed in males in the pre-differentiation phase, suggests that fatty acid metabolism plays an important role in sex differentiation in tambaqui.