Leptin-mediated modulation of steroidogenic gene expression in hypoxic zebrafish embryos: implications for the disruption of sex steroids.

Hypoxia can impair reproduction of fishes through the disruption of sex steroids. Here, using zebrafish (Danio rerio) embryos, we investigated (i) whether hypoxia can directly affect steroidogenesis independent of pituitary regulation via modulation of steroidogenic gene expression, and (ii) the role of leptin in hypoxia-induced disruption of steroidogenesis. Exposure of fertilized zebrafish embryos to hypoxia (1.

Major human Hepatitis A virus genotype in Hong Kong marine waters and detection by real-time PCR.

Marine waters from seven sites around Hong Kong with varying levels of sewage pollution were analyzed for Hepatitis A virus (HAV) by PCR cloning and DNA sequencing of the highly variable VP1/2A junction of the HAV genome. Phylogenetic analysis of 10 PCR clones from each of the HAV-positive marine sites indicated that human HAV genotype IB is the most widely distributed type in Hong Kong waters. A sensitive and quantitative TaqMan-based PCR method targeting the 5'-noncoding region (5'-NCR) of HAV was used to quantify HAV particles in marine water samples along with the total Escherichia coli counts being enumerated on TBX medium for comparison.

Leptin: clue to poor appetite in oxygen-starved fish.

Hypoxia is the most widespread deleterious consequence of eutrophication and has become a major cause of fishery decline. One feature of chronic exposure to hypoxia in fish is inhibition of feeding. In this study, we investigated if the gene that encodes the appetite-suppressing hormone leptin is regulated by hypoxia in zebrafish (Danio rerio).

Enhancement of hypoxia-induced gene expression in fish liver by the aryl hydrocarbon receptor (AhR) ligand, benzo[a]pyrene (BaP).

Fish in polluted coastal habitats commonly suffer simultaneous exposure to both hypoxia and xenobiotics. Although the adaptive molecular responses to each stress have been described, little is known about the interaction between the signaling pathways mediating these responses. Previous studies in mammalian hepatoma cell lines have shown that hypoxia-inducible factor (HIF)- and/or aryl hydrocarbon receptor (AhR)-activated gene expression is suppressed following co-exposure to hypoxia and the hallmark AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).