Copy number related transgene expression and mosaic somatic expression in hemizygous and homozygous transgenic tilapia (Oreochromis niloticus).

Three lines of transgenic tilapia (Oreochromis niloticus) fish were generated with a construct containing a lacZ reporter gene spliced to a 4.7 kb 5' regulatory region of a carp beta actin gene. All these three lines contain different copy numbers of transgenes and the levels of lacZ expression were found to be related to transgene copy number. Mosaic patterns of somatic lacZ expression were observed in these three lines which differed between lines but were consistent within a line. We also observed that expression of the reporter gene in homozygous transgenic fish was approximately two-fold greater than in the hemizygous transgenics. Analysis of expression of the reporter gene on a tissue-to-tissue basis demonstrated that lacZ expression of the reporter gene in stably transformed fish occured with variable intensity in different organs and tissues and was also sometimes variable in different cells of the same tissue in Gland G2 generations of the transgenic lines.