Genes involved in sex determination and the influence of temperature during the sexual differentiation process in fish: A review

This review attempts to group the recent hypotheses involved in the complex system of determination and sex differentiation in fish. Based on recent literature, we relate the key genes involved in the genomic cascade as the Cyp19, Dmrt1, Sox9, Foxl2, Esr, Dax1, Sf1 and Amh1, and still little known action of temperature on them. As the sex reversal is a highly desired process in fish farming aiming at obtaining male mono-sexual populations (due to weight gain of males), several techniques based on direct and indirect manipulation of phenotypic sex are being tested. Recent surveys show the use of temperature as alternative to the process of sex reversal. However, high or low temperatures have limited effect, in addition to there being a window of sex reversal in which temperature acts, varying from species to species. Thus, we draw a parallel with the role of temperature in the process of sex reversal and its effect on genes of the genomic cascade, which has been the subject of several studies that attempt to explain how temperature would be acting in this process. Intracellular receptors, such as those used for steroid hormones, act as transcription factors to regulate target genes moving between the nucleus and cytoplasm and, in the hormone absence, are linked to the complex of heat shock protein 90 kDa (Hsp90). Through this mechanism, it is possible to predict that fluctuations in temperature can influence the action of hormones, the increased transcription of genes involved in steroidogenesis and hence in sexual differentiation, becoming an alternative to explain where the temperature is acting. However, this literature review discusses the correlations between the genomic cascade, the action of intracellular receptors and the influence of temperature within this large system of determination and sex differentiation in fish.