Comparative expression analysis in mature gonads, liver and brain of turbot ( Scophthalmus maximus) by cDNA-AFLPS

Turbot is one of the most important farmed fish in Europe. This species exhibits a considerable sexual dimorphism in growth and sexual maturity that makes the all-female production recommended for turbot farming. Our knowledge about the genetic basis of sex determination and the molecular regulation of gonad differentiation in this species is still limited. Our goal was to identify and compare gene expression and functions between testes and ovaries in adults in order to ascertain the relationship between the genes that could be involved in the gonad differentiation or related to the sex determination system. The identification of differentially expressed sex related genes is an initial step towards understanding the molecular mechanisms of gonad differentiation. For this, we carried out a transcriptome analysis based on cDNA-AFLP technique which allowed us to obtain an initial frame on sex-specific gene expression that will facilitate further analysis especially along the critical gonad differentiating period. With the aim of widening the study on sex-biased gene expression we reproduced the same experiments in two somatic tissues: liver and brain. We have selected the liver because it is the most analyzed one regarding sexual dimorphic gene expression and due to its importance in steroid hormones metabolism and the brain because the functional relationship between brain and gonad is documented. We found slight but important differences between sexes which deserve further investigation. ► Sex-biased gene expression was analyzed in three tissues of turbot by cDNA-AFLP. ► Some sex-specific sequences were detected in gonad analysis. ► RT-qPCR showed a higher expression in males than in females of MNS1 and NEK-10 genes. ► Few expression differences were detected between the brains and liver of both sexes. ► RT-qPCR revealed that C9 gene is up-regulated in the liver of males.