Copy Number Related Transgene Expression and Mosaic Somatic Expression in Hemizygous and Homozygous Transgenic Tilapia (Oreochromis Niloticus)

Three lines of transgenic tilapia (Oreochromisniloticus) fish were generated with a constructcontaining 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 oftransgenes and the levels of lacZ expressionwere 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 observedthat expression of the reporter gene in homozygoustransgenic fish was approximately two-fold greater than in the hemizygous transgenics. Analysis of expressionof the reporter gene on a tissue-to-tissue basisdemonstrated that lacZ expression of thereporter gene in stably transformed fish occured withvariable intensity in different organs and tissues andwas also sometimes variable in different cells of thesame tissue in G1and G2 generations of the transgenic line