Comparative transcriptome analysis reveals sex bias in expression patterns of genes related to sex steroids and immunity in the skin of spinyhead croaker Collichthys lucidus.

Fish skin is the first barrier against external invasion, and also an important interface for communication between males and females during reproduction. Nonetheless, sexual dimorphism in the physiology of fish skins is still poorly understood. Herein, transcriptomes of skin were comparatively analysed between males and females in spinyhead croaker, Collichthys lucidus. Totally, 170 differentially expressed genes (DEG) were detected, including 79 female-biased genes and 91 male-biased genes. Gene ontology (GO) annotation items of the DEGs were mainly enriched in biological process items (86.2%), including regulation of biological processes, responses to chemical and biological stimuli, transport and secretion, movement, immune response, tissue development, etc. In KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis, the male-biased genes were enriched in pathways including those related to immunity such as the TNF signalling pathway and IL-17 signalling pathway, whereas the female-biased genes were enriched in pathways including those related to female steroids such as ovarian steroidogenesis and oestrogen signalling pathway. In addition, odf3 was found to be a male-specific expression gene, being a candidate marker for phenotypic sex. Thus, the sexual difference in gene expression in fish skin in spawning season was uncovered by transcriptome analysis for the first time, providing new insights into sexual dimorphism in the physiology and functions of fish skin.

Chronic exposure to paclobutrazol causes hepatic steatosis in male rockfish Sebastiscus marmoratus and the mechanism involved.

Paclobutrazol (PBZ) is a triazole-containing fungicide which is widely used in agriculture. Acute toxicity can follow its extensive use but it is generally weaker than traditional pesticides such as organochlorine and organophosphorus. However, its adverse effects on aquatic organisms need to be investigated. This study was conducted to investigate the effect of PBZ exposure on the hepatic lipid metabolism of Sebastiscus marmoratus. After PBZ exposure for 50 days, hepatic lipid droplets were enlarged and the hepatic total lipid, triglyceride, total cholesterol and free fatty acid content had increased in a dose dependent manner compared to the control. The mRNA expression of lipid metabolism associated genes such as peroxisome proliferator-activated receptors (PPARs), androgen receptor, acetyl-CoA carboxylase 1, fatty acid synthesis, fatty acid bing protein 4, liver X receptor α (LXRα) and stearoyl-CoA desaturase were up-regulated by PBZ exposure. These results indicated that triazole-containing fungicides might affect the metabolism and health of fish via the multi-signal pathways of nuclear receptors such as PPARs and LXR.

Effects of paclobutrazol exposure on antioxidant defense system in Sebastiscus marmoratus.

This study was conducted to detect the effects of paclobutrazol (PBZ) at environmental concentration on the antioxidant defense system in Sebastiscus marmoratus. Fish were exposed to concentrations of PBZ (10, 100, 1,000 ng/L) for 50 days. The results showed: (1) The glutathione contents in the liver and brain were significantly decreased in a dose-dependent manner. (2) The activities of glutathione S-transferases (GST) and catalase in liver and brain were inhibited as the increase of PBZ concentration. A highest 2.16-fold (p = 0.05) and 11.54-fold (p < 0.001) reduction of GST activity in the liver and brain respectively was observed in 1,000 µg/L group. (3) The activities of glutathione peroxidase in liver were inhibited. These results suggest that the exposure of PBZ would influence the antioxidant ability of S. marmoratus.

Exposure to paclobutrazol disrupts spermatogenesis in male Sebastiscus marmoratus.

Paclobutrazol (PBZ) is triazole-containing fungicides and widely used in agriculture as an efficient plant growth retardant. However, far fewer studies addressing the reproductive toxicity of PBZ on fishes are available. The present study was conducted to investigate the effects of PBZ at environmentally relevant concentrations on testicular development in male rockfish Sebastiscus marmoratus and to gain insight into its mechanism of action. After exposure to 10, 100 and 1000 ng/L PBZ for 50 d, although the gonadosomatic index did not show a significant alteration, there was a reduced number of mature sperm and an abundance of the late stages of spermatocysts in the testes. The activity of γ-glutamyl transpeptidase (which is used as a Sertoli cell marker) was decreased in a dose-dependent manner after PBZ exposure, which might be a result of the reduction in FSHß expression in the brain. The toxicity induced by accumulation of PBZ in the brain might be primary cause impacting the spermatogenesis via brain-pituitary-gonad pathway.