Somatic transgenesis in Nile tilapia (Oreochromis niloticus)

Abstract

There were two main objectives for this project. The first was to investigate the fate and persistence of transgene DNA after direct injection into the somatic cells of tilapia. This was achieved using the bacterial reporter gene lacZ. The difference in expression levels gained using tilapia β-actin/lacZ and carp β-actin/lacZ constructs were also investigated, as well as the effect of co-injection of these constructs with the linear tilapia β-actin enhancer element, isolated from intron 1 of the tilapia β-actin promoter. The second of the objectives was to investigate the effect on growth of juvenile tilapia after somatic gene transfer of an ‘all-tilapia’ growth hormone plasmid construct (tiβAP/tiGH) as well as the opAFP/csGH construct into the muscle tissue of tilapia fish.

The results suggest that the tilapia promoter sequence gives rise to higher gene expression probably owing to the greater homology of this promoter when compared to that from the other species. Co-injection of the tilapiine enhancer element from intron I significantly boosted levels of gene expression. It was found that the gene product was mobile around the body, unlike the DNA itself which remained, for the most part, in the myofibres around the site of injection. On injection of either of the growth hormone plasmids, there was a putative endocrine controlled down-regulation of endogenous GH, making GH-injected fish show reduced growth as compared with controls. A putative contributing limiting factor may be attributed to the quantity of plasmid DNA which can become nuclear, since the active nuclear uptake mechanism can become saturated.

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