Abstract
BackgroundControlling sex ratios is essential for the aquaculture industry, especially in those species with sex dimorphism for relevant productive traits, hence the importance of knowing how the sexual phenotype is established in fish. Turbot, a very important fish for the aquaculture industry in Europe, shows one of the largest sexual growth dimorphisms amongst marine cultured species, being all-female stocks a desirable goal for the industry. Although important knowledge has been achieved on the genetic basis of sex determination (SD) in this species, the master SD gene remains unknown and precise information on gene expression at the critical stage of sex differentiation is lacking. In the present work, we examined the expression profiles of 29 relevant genes related to sex differentiation, from 60 up to 135 days post fertilization (dpf), when gonads are differentiating. We also considered the influence of three temperature regimes on sex differentiation.ResultsThe first sex-related differences in molecular markers could be observed at 90 days post fertilization (dpf) and so we have called that time the onset of sex differentiation. Three genes were the first to show differential expression between males and females and also allowed us to sex turbot accurately at the onset of sex differentiation (90 dpf): cyp19a1a, amh and vasa. The expression of genes related to primordial germ cells (vasa, gsdf, tdrd1) started to increase between 75–90 dpf and vasa and tdrd1 later presented higher expression in females (90-105 dpf). Two genes placed on the SD region of turbot (sox2, fxr1) did not show any expression pattern suggestive of a sex determining function. We also detected changes in the expression levels of several genes (ctnnb1, cyp11a, dmrt2 or sox6) depending on culture temperature.ConclusionOur results enabled us to identify the first sex-associated genetic cues (cyp19a1a, vasa and amh) at the initial stages of gonad development in turbot (90 dpf) and to accurately sex turbot at this age, establishing the correspondence between gene expression profiles and histological sex. Furthermore, we profiled several genes involved in sex differentiation and found specific temperature effects on their expression.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2142-8) contains supplementary material, which is available to authorized users.
Highlights
Controlling sex ratios is essential for the aquaculture industry, especially in those species with sex dimorphism for relevant productive traits, the importance of knowing how the sexual phenotype is established in fish
Eighty-nine females and eighty-five males could be genetically sexed because the SmaUSC30 marker was informative, the remaining six samples being removed from this analysis since they could not be sexed
Turbot sex differentiation is ongoing at 90 dpf and sex can be distinguished by the expression levels of three genes when fish are 5–6 cm length: cyp19a1a, amh and vasa; while later females are discriminated by the expression of cyp19a1a
Summary
Controlling sex ratios is essential for the aquaculture industry, especially in those species with sex dimorphism for relevant productive traits, the importance of knowing how the sexual phenotype is established in fish. Considering its consequences over the lifespan of an organism and its influence on population demography, it is thought that the sex determination (SD) mechanism should be under strong selection forces [2]. When dmY, belonging to the DM family of Robledo et al BMC Genomics (2015) 16:973 transcription factors like DMRT1 and DM-W, was found to be the sex determining gene (SDG) of the fish Oryzias latipes, a biased and recurrent recruitment of specific SDGs or families throughout evolution was suggested [9]. Later findings in fish do not seem to support this hypothesis
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