Early developmental expression of two insulins in zebrafish (Danio rerio)

Abstract

We have cloned a second insulin gene in zebrafish and studied temporal and spatial expression of two zebrafish insulin genes. Zebrafish insulin-a (insa) and -b (insb) mRNAs are derived from two different DNA contigs on chromosomes 5 and 14, respectively, representing two different insulin genes. Real-time PCR studies suggest that insa is a maternal and also a postzygotic transcript. insa was observed at 1 h postfertilization (hpf) and was rapidly degraded by 6 and 12 hpf but induced at 24 hpf (i.e., after pancreas formation). Expression levels at 24 hpf were ϳ220-fold higher than at 6 hpf and were significantly different from earlier time points. At 72 hpf (at time of hatching), zebrafish insa mRNA levels tended to be higher than at 24 hpf and were ϳ727-fold higher compared with 6 hpf. This further increase in insa expression may be one of the many rapid physiological changes associated with hatching. insb expression was observed from 1 hpf and was significantly decreased from 12 hpf onward. Its expression levels at 12 and 24 hpf were approximately twofold and sixfold lower, respectively, compared with expression at 6 hpf. insb expression levels at 48 hpf were significantly lower than at 24 hpf but not different from 72 hpf. Expression levels at 72 hpf were ϳ61-fold lower than at 6 hpf. In situ hybridization studies showed insb expression in proliferating blastomeres at 3 and 4 hpf. At later time points, insb expression was restricted to the brain and pancreas (24 and 48 hpf). insa expression was observed in the pancreas at 24 and 48 hpf. Expression of insb in blastomeres and head suggests that insb could be acting as a pro-growth, survival, and neurotrophic factor during development. Pancreatic insa and insb may both be involved in regulation of glucose homeostasis as in mammals.insulin; gene duplication; polymerase chain reaction IT IS BECOMING CLEAR that single gene duplication and whole genome duplication have been typical rather than atypical events in the evolutionary history of many species. Two insulin genes have now been identified in rat, mouse, Xenopus laevis, and channel catfish (5,18,20,32). It was hypothesized that the gene duplication events in rodents were different from those occurring in X. laevis and channel catfish (2, 25, 33). The two X. laevis preproinsulins are more similar to each other than the other species and resulted from an insulin gene duplication that occurred during amphibian radiation (33). Recent evidence suggests that a genome duplication event occurred before teleost radiation in ray-finned fish lineage, after divergence from lobe-finned fishes (2, 25). Phylogenetic analysis using fish insulin genes suggests that insulin gene duplication occurred before the divergence of fugu and zebrafish, suggesting that insulin gene duplication occurred as part of a whole genome duplication event that occurred before teleost radiation (15).Insulin is generally believed to be exclusively expressed by pancreatic ␤-cells. It has multiple regulatory roles including mediation of glucose homeost...

A study of somatolactin actions by ectopic expression in transgenic zebrafish larvae

“…A study of somatolactin actions in transgenic zebrafish reproduction in teleosts. IGFs have also been found to be required for primordial germ cell migration and survival (Mommsen & Plisetskaya 1991, Papasani et al 2006. However, SLs did not appear to enhance IGF3 gene expression in this study.…”

Towards Fish Lipid Nutrigenomics: Current State and Prospects for Fin-Fish Aquaculture

“…Insulin has been identified in numerous fish (Conlon 2001), and often two insulin genes are present (Kavsan et al 1993;Mommsen et al 2001;Papasani et al 2006). As in mammals, insulin has an anabolic action in fish, enhancing lipid storage by activating lipogenesis, and increasing protein synthesis and body growth (Nelson and Sheridan, 2006).…”

Sexual dimorphism in hepatic gene expression and the response to dietary carbohydrate manipulation in the zebrafish (Danio rerio)

“…lasting from the larval stage to sexually mature adult) and the potential role of sexual dimorphism in the regulation of nutrient partitioning. These data are important in a variety of contexts, including improving our fundamental understanding of hepatic function and adaptability in fishes, design of alternative diets for aquaculture species (Trushenski et al, 2006) and the use of fish models in biomedical research (Papasani et al, 2006;Elo et al, 2007).…”