Mendelian transmission, transgene dosage and growth phenotype in transgenic tilapia (Oreochromis hornorum) showing ectopic expression of homologous growth hormone.
Transgenic tilapia (Oreochromis hornorum urolepis) were produced by the microinjection of a transgene containing the tilapia growth hormone (tiGH) cDNA under the regulatory sequences derived from the human cytomegalovirus (CMV) into early embryos. A male containing 1 copy/cell of the transgene was selected to establish a transgenic tilapia line. Genomic DNA was extracted from fin tissue and embryos and was analysed by PCR. The transgene was transmitted to F1-F4 generations in a Mendelian fashion. Biochemical analyses indicated lower levels of cholesterol, free alanine and aspartic acid in the muscle of transgenic fish compared with wild type tilapia. 6 transgenic homozygous (F2+/+), 8 transgenic heterozygous (F2-/+) tilapia and 14 non-transgenic siblings were maintained in the same pond for 3 months starting at 4 months of age and growth rate was recorded. Transgenic F2-/+ and F2+/+ progeny were 62 and 31% heavier than non-transgenic siblings at 7 months of age (P = 0.005 and P = 0.07, respectively), suggesting a transgene-dosage effect.