Molecular cloning and functional analysis of zebrafish high-density lipoprotein-binding protein

High-density lipoprotein-binding protein (HBP) plays a pivotal role in the endocrine regulation of both lipids and cholesterol. This first study of the zebrafish (Danio rerio) HBP gene in a piscine provides information on the complex molecular events that regulates lipid and cholesterol functions in fish, and allows a comparison with starvation and hormonal regulation. One identical zebrafish HBP cDNA clone was obtained from a 24-h-old zebrafish cDNA library. Zebrafish HBP is composed of 1273 amino acids as residues. The 1273-aa of HBP has 87.8% and 87.0% similarities to human and chicken HBP, respectively. Real-time reverse transcription polymerase chain reaction (RT-PCR) analysis showed that HBP is highly expressed in the 36 h of the developmental stage after fertilization as compared to other stages. As to tissue-specific expression, the HBP is highly expressed in the fin, liver and ovary. In the starvation experiment, results show significant differences between the control group and the group after 3-week starvation. After injecting GH, IGF-I, IGF-II or insulin, no significant differences were shown between the control and the experimental groups. These results suggest that in vivo HBP expression is not regulated by the insulin family or by growth hormone, but other factors present during the starvation may down- or up-regulate the HBP. Although the exact function of the HBP is unknown, its high expression in the liver and ovary suggests a role for this molecule in the cumulative efficiency of fish intake of food or lipid transfer; these results can possibly be applied to aquaculture in the near future.