Mendelian transmission, transgene dosage and growth phenotype in transgenic tilapia (Oreochromis hornorum) showing ectopic expression of homologous growth hormone

Gene transfer has offered a new tool for the development of improved fish s trains for aquaculture. However, characterization is required before these strains can be introduced into national aquaculture programs. Transgenic ti lapia (O. hornorum urolepis) were produced by the microinjection into early embryos of a transgene containing the tilapia growth hormone (tiGH) cDNA u nder the regulatory sequences derived from the human cytomegolovirus (CMV). A male containing 1 copy/cell of the transgene was selected to establish a transgenic tilapia line. The transgene was transmitted to F-1-F-4 generati ons in a Mendelian fashion. Previous studies showed ectopic, low level expr ession of tiGH in brain, heart, gonad, liver and muscle cells of transgenic tilapia. Biochemical analyses indicated lower levels of cholesterol, free alanine and aspartic acid in the muscle of transgenic animals. Four month o ld transgenic homozygous (F-2(+/+)) and heterozygous (F-2(-/+)) tilapia and non-transgenic siblings (N-TRANSGENICS = 14; N-CONTROLS = 11; N-F2(-/+) = 8; N-F2(+/+) = 6) were studied for 3 months grown communally in the same po nd. Transgenic (F-2(-/+) + F-2(+/+)), F-2(-/+), and F-2(+/+) progeny were l arger than non-transgenic siblings at P = 0.009, P = 0.005 and P = 0.07 (St udent t-test), respectively, suggesting a transgene-dosage effect. These re sults indicate stable germ line transformation in this fast-growing transge nic tilapia line. (C) 1999 Elsevier Science B.V. All rights reserved.