In Drosophila melanogaster, sex is determined at the preblastoderm stage via an Xchromosome counting mechanism. During this process embryos that carry two X chromosomes begin to develop as females while embryos with one X start the male developmental program. The Xlinked genes involved in sex determination, also called Xsignal elements (XSEs), are: sisterlessA (sisA), sisterlessB (sisB), unpaired (upd), and runt. These genes are responsible for the transcriptional activation of the master regulatory gene Sexlethal (Sxl). Expression of Sxl is initially accomplished only in females through activation of the establishment promoter SxlPe. Later in development, Sxl is transcribed in both sexes through a maintenance promoter, SxlPm, but functional Sxl protein is only produced in female flies. Since Sxl is at the top of the sex determination cascade, understanding its regulation is key to comprehend the process of sex determination. The experiments in this dissertation were designed to better understand two aspects of the sex determination mechanism: How the protein encoded by XSE element sisA interacts with SxlPe, and how the transition from regulation by SxlPe to regulation by SxlPm occurs. The sisA protein (SisA), as part of the bZIP protein family, is thought to bind to its target as a dimer, but a dimerization partner has not yet been found. This work uses knockouts and germline clones to examine interaction between sisA and three SisA partner candidates, atf4, CG16813, and CG16815. Although the evidence described here suggest that none of the three SisA partner candidates genetically interact with Sis, we cannot rule out the possibility of redundancy between the different candidate proteins. This research unravels the timing and regulation of SxlPm expression. I have shown, contrary to previous thought, that expression of SxlPe and SxlPm overlaps for a brief period. Several of the same proteins that are involved in the regulation of SxlPe, including the XSE sisB, also regulate SxlPm. This sex specific regulation leads to a sexually dimorphic pattern of activation and early expression of SxlPm. A common enhancer region was found to regulate SxlPe as well as SxlPm. These results highlight the importance of the transition between SxlPe and SxlPm for the proper establishment of sex determination and have implications for how the sex determination mechanism evolved.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Tropical forests play vital role in maintaining the stability and quality of the environment, protecting the soil and water resources, conserving the biodiversity, protecting cultural and recreational values, which contribute to improving the quality of life of the population. Being the germplasm of forest species a wealth to be used and preserved. Schinus terebinthifolius (Anacardiaceae) has medicinal, alimentary and ecological properties, besides being destined for the recomposition of degraded areas of permanent preservation. However, there are few studies on the cytogenetics characterization and promotion growth of this species. Thus, aiming for conservation and sustainable use, the objective is to characterize cytogenetically this species, assess the quality of the seeds S. terebinthifolius from individuals of different accessions of populations of Rio Grande do Sul, as well as, to evaluate the effect of the interaction of Trichoderma spp. on the contamination and in vitro germination and ex vitro vegetative growth of S. terebinthifolius. For the determination of chromosome number were used tissues of root tips. In the germination study, the parcels with seeds were kept in a climatic chamber with a photoperiod of 16 hours at the temperature of 20°C (+/- 2°C). To the study the interaction between S. terebinthifolius and Trichoderma spp. were evaluated the isolates TSM1 and TSM2 of Trichoderma viride, 2B2 and 2B22 of Trichoderma harzianum for the in vitro experiment, through the cellophane technique and the ex vitro experiment was conducted in a greenhouse, where were evaluated the effects of the isolates 2B2 and 2B22 and the commercial product Trichodermil®, all in the presence and absence of growth regulator Stimulate®. It is concluded that the chromosome number of the species S. terebinthifolius determined for 22 accessions collected in Rio Grande do Sul is 2n = 28, indicating that there isn't intraspecific variability. The quality of the seeds of S. terebinthifolius shows great heterogeneity among the different accessions collection. With the technique of in vitro cellophane, all four isolates of Trichoderma spp. tested are efficient in controlling fungal contamination of seeds. In ex vitro cultivation, the difference was significant growth in leaf area index for strain 2B2 / As florestas tropicais desempenham função vital na manutenção da estabilidade e qualidade do meio ambiente, protegem o solo e os recursos hídricos, conservam a diversidade biológica, protegem os valores culturais e recreativos, que contribuem com a melhoria da qualidade de vida da população. Sendo o germoplasma de espécies florestais uma riqueza a ser utilizada e preservada. Schinus terebinthifolius (Anacardiaceae) possui propriedades medicinais, alimentícias e ecológicas, além de serem destinados à recomposição de áreas degradadas de preservação permanente. No entanto, ainda são poucos os estudos sobre a caracterização citogenética e promoção de crescimento dessa espécie. Assim, visando à conservação e a utilização sustentável, objetiva-se caracterizar citogeneticamente esta espécie, avaliar a qualidade das sementes de S. terebinthifolius provenientes de indivíduos de diferentes acessos do Rio Grande do Sul, bem como, avaliar o efeito da interação de Trichoderma spp. na contaminação e germinação in vitro e no crescimento vegetativo ex vitro de S. terebinthifolius. Para a determinação do número de cromossomos, foram utilizados tecidos de pontas de raízes. No estudo de germinação, as parcelas com as sementes foram mantidas em câmara climática com fotoperíodo de 16 horas à temperatura de 20°C (+/- 2°C). Para o estudo da interação entre S. terebinthifolius e Trichoderma spp. foram avaliados os isolados TSM1 e TSM2 de Trichoderma viride, 2B2 e 2B22 de Trichoderma harzianum para o experimento in vitro, através da técnica do papel celofane e o experimento ex vitro foi realizado em casa de vegetação, onde se avaliou os efeitos dos isolados 2B2 e 2B22, e o produto comercial Trichodermil®, todos na presença e ausência do regulador de crescimento Stimulate®. Conclui-se que o número de cromossomos da espécie S. terebinthifolius determinado para 22 acessos coletados no Rio Grande do Sul é de 2n = 28, indicando que não ocorre variabilidade intraespecífica. A qualidade das sementes de S. terebinthifolius apresenta grande heterogeneidade entre os diferentes acessos de coleta. Com a técnica in vitro do papel celofane, os quatro isolados de Trichoderma spp. testados são eficientes no controle da contaminação fúngica das sementes. No cultivo ex vitro, observou-se diferença significativa de crescimento no índice de área foliar para o isolado 2B2;