Abstract
The spotted scat (Scatophagus argus) is an economically important cultured marine fish that exhibits a typical sexual size dimorphism (SSD). SSD has captivated considerable curiosity for farmed fish production; however, up till now the exact underlying mechanism remains largely unclear. As an important digestive and metabolic organ, the liver plays key roles in the regulation of fish growth. It is necessary to elucidate its significance as a downstream component of the hypothalamic-pituitary-liver axis in the formation of SSD. In this study, the liver physiological differences between the sexes were evaluated in S. argus, and the activity of several digestive and metabolic enzymes were affected by sex. Females had higher amylase, protease, and glucose-6-phosphate dehydrogenase activities, while males exhibited markedly higher hepatic lipase and antioxidant enzymes activities. A comparative transcriptomics was then performed to characterize the responsive genes. Illumina sequencing generated 272.6 million clean reads, which were assembled into 79,115 unigenes. A total of 259 differentially expressed genes were identified and a few growth-controlling genes such as igf1 and igfbp1 exhibited female-biased expression. Further analyses showed that several GO terms and pathways associated with metabolic process, particularly lipid and energy metabolisms, were significantly enriched. The male liver showed a more active mitochondrial energy metabolism, implicating an increased energy expenditure associated with reproduction. Collectively, the female-biased growth dimorphism of S. argus may be partially attributed to sexually dimorphic metabolism in the liver. These findings would facilitate further understanding of the nature of SSD in teleost fish.
Highlights
IntroductionThe differences of liver physiological indicators between male and female S. argus were examined and a comparative transcriptome analysis was further performed to characterize the responsive genes in the liver, aiming to provide a global view of the sexual differences in hepatic biological processes and to explore the potential pathways responsible for inducing sexual size dimorphism (SSD)
Licensee MDPI, Basel, Switzerland.Sexual size dimorphism (SSD), known as sexual growth dimorphism, is commonly defined as the significant differences in body size and growth rate between males and females [1]
We found that female S. argus had significantly higher hepatic amylase and protease activities than males; several differential expression genes (DEGs) involved in proteolysis process such as transmembrane protease serine 2, transmembrane protease serine 9, and carboxypeptidase E were identified as female-biased genes (Table S4), suggesting a better utilization of protein in females
Summary
The differences of liver physiological indicators between male and female S. argus were examined and a comparative transcriptome analysis was further performed to characterize the responsive genes in the liver, aiming to provide a global view of the sexual differences in hepatic biological processes and to explore the potential pathways responsible for inducing SSD. Such data would be of value to further illuminate the nature of the mechanisms that give rise to SSD in this species
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