Abstract
The rock bream (Oplegnathus fasciatus) is a typical fish with a unique multiple sex chromosome system. In this study, we investigated the gene expression profiling in the gonads and brains of both males and females using RNA-Seq to identify sex-related genes and pathways. In accordance with the dimorphic expression profiles, combined with Gene ontology and KEGG enrichment analyses, a number of potential genes and pathways associated with sex determination were obtained from transcriptional analysis, especially some sex-biased genes and pathways. Next, we selected 18 candidate genes and analyzed their expression in different tissues and developmental stages. We found that the expression levels of Amh, Dmrt1, Sox9, Dmrtb1, and Nanos2 were significantly higher in the testis than those in the ovary or other tissues, whereas the expression levels of ZP4, Bouncer, RNF208, FoxH1, and TOB were significantly higher in the ovary than those in the testis. Furthermore, the expression levels of these genes in different developmental stages of gonads also showed sexually dimorphic patterns, suggesting that they might play important roles during gonadal development. These genes are useful markers for investigating sex determination and differentiation in rock bream. The findings of this study can provide insights into the molecular mechanisms of sex determination and differentiation in fish with multiple sex chromosome systems.
Highlights
Teleost fish display an amazing diversity of sex-determination systems, such as XX/XY, ZZ/ZW, XX/ XO, and ZZ/ZO
For a better understanding of sex determination and differentiation in the rock bream, we investigated the gene expression profiles in the gonads and brains of males and females by conducting a comparative transcriptome analysis and screened potential sex-related genes and pathways
We detected a low number of differentially expressed gene (DEG) in the brains of males and females, which indicated fewer differences in the brain between sexes at the transcriptomic level
Summary
Teleost fish display an amazing diversity of sex-determination systems, such as XX/XY, ZZ/ZW, XX/ XO, and ZZ/ZO. The rock bream (Oplegnathus fasciatus), a member of the Oplegnathidae family of the Centrarchiformes, is a Dimorphic Expression of Sex-Related Genes commercially important rocky reef fish native to East Asia and has been reported as a typical fish with multiple X1X1X2X2/X1X2Y sex chromosome system (Xu et al, 2012; Xue et al, 2016; Xu et al, 2019). The whole genomes of both male and female rock breams were sequenced, assembled, and analyzed, and their results suggested that the neo-Y chromosome probably originated from the centric fusion of acrocentric chromosomes (X1 and X2 chromosomes) (Shin et al, 2018; Xiao et al, 2019; Xiao et al, 2020) These studies have contributed to the understanding of sex determination in species with a unique multiple sex chromosome system. To date, little is known about the molecular pathways and regulatory mechanisms of sex determination in fish with multiple sex chromosome system
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