Transgene activity following somatic transgenesis in Nile tilapia Oreochromis niloticus

A detailed study was made of the persistence and expression of a plasmid-enclosed reporter gene construct after intramuscular injection into the somatic muscle tissue of juvenile Nile tilapia Oreochromis niloticus and also the effect of injecting a potentially growth-promoting gene construct. The plasmid-enclosed DNA proved stable at the site of injection, lasting in some cases for up to 6 months, and was, at a very low frequency, detected in gonad tissue, indicating occasional substantial movement from the injected muscle site. It was observed that the reporter gene and regulatory sequences were also functional within the somatic cells. In a comparison of expression levels by direct somatic injection, the 1.6 kb tilapia beta-actin regulatory sequence (ti beta AP) resulted in c. three-fold higher beta-galactosidase activity than the 4.7 kb carp beta-actin regulatory sequence (c beta AP) when spliced to the lacZ gene. The enhancer element near the end of. rst intron in the tibAP, when co-injected with tibAP/lacZ plasmid at a 3: 1 ratio, drove significantly higher reporter activity in somatic cells than the ti beta AP/lacZ sequence alone. The introduction of a growth-promoting construct, the Nile tilapia growth hormone gene driven by a ti beta AP, yielded no detectable growth enhancement. (C) 2007 The Authors.