Insight to new genes with sex-biased to bony-tongued fishes: Differentially expressed genes in adult individuals of Arapaima gigas revealed by RNA-Seq

The Arapaima gigas is an endemic fish to the Amazon basin and with great potential for aquaculture, although its reproduction in captivity is limited by the absence of sexual dimorphism. The demand increase for pirarucu in the Northern region of Brazil, has led to new studies on the reproduction of the species. Thus, we aimed to investigate patterns of sex-biased genes in brain and gonad tissues of A. gigas. A total of of 451,490,808 short sequencing reads were produced using the SOLiD v4 plus sequencing platform. An average of similar to 30% of sequencing reads were mapped to Asian arowana reference cDNAs, species that belong to the same group of bony-tongue fishes. Gene expression analysis identified 305 sex-biased genes for the brain, with 297 genes up-regulated in females and only eight genes up-regulated in males. The analysis of the gonads identified 120 sex-biased genes, with 110 genes up-regulated in females and only ten genes up-regulated in males. Gene ontology analysis found more than 50 terms enriched for the sex-biased genes in a wide range of pathways suggesting that multiple functions and processes differ between the sexes. Thus, the following areas of interest were approached: sex steroids/hormones, organism development process and macromolecule biosynthetic process, which exhibited sex-biased gene expression; these areas are known to influence sexual development in other species. Lastly, the information obtained in this study concerning the sex-biased genes in the A. gigas species is a contribution to further studies approaching the processes of gonadal development, and downstream molecular mechanisms in species.