Genetic engineering of livestock is expected to have a major effect on the agricultural industry. However, accurate assessment of the consequences of transgene expression is impossible without multigenerational studies. A systematic study of the beneficial and adverse consequences of long-term elevations in the plasma levels of bovine growth hormone (bGH) was conducted on two lines of transgenic pigs. Two successive generations of pigs expressing the bGH gene showed significant improvements in both daily weight gain and feed efficiency and exhibited changes in carcass composition that included a marked reduction in subcutaneous fat. However, long-term elevation of bGH was generally detrimental to health: the pigs had a high incidence of gastric ulcers, arthritis, cardiomegaly, dermatitis, and renal disease. The ability to produce pigs exhibiting only the beneficial, growth-promoting effects of growth hormone by a transgenic approach may require better control of transgene expression, a different genetic background, or a modified husbandry regimen.

https://science.sciencemag.org/content/sci/244/4910/1281.full.pdf

Genetic engineering of livestock.

To generate stable lines of transgenic fish, early zebrafish embryos were injected with high concentrations of a linear bacterial plasmid. After injection, the foreign DNA was converted into a high molecular weight form and then amplified approximately tenfold during the initial rapid cleavages characteristic of the early embryo prior to gastrulation. While most of this DNA was subsequently degraded during gastrulation, some of the foreign sequences survived the gastrula stage and could be found in most of the injected fish at 3 weeks of age. Only about 5% of fish analysed 4 months after the injection retained foreign DNA in their fins, usually at less than one copy per cell. One of these fish was also found to contain about 100 copies per cell of foreign DNA in a fraction of its germ cells. Approximately 20% of the F1 offspring from this germ-line-positive parent inherited the foreign DNA, whereas 50% of F2 progeny obtained from an identified F1 individual inherited these sequences. The 50% transmission rate in F2 progeny was as expected for a single, heterozygous genomic insert. These observations indicate that injected DNA can be integrated into the fish genome, that the resulting transgenic fish are mosaic and that some of these mosaic individuals give rise to stable lines of transgenic fish.

Replication, integration and stable germ-line transmission of foreign sequences injected into early zebrafish embryos

Fish represent the largest and most diverse group of vertebrates. Their evolutionary position relative to other vertebrates and their ability to adapt to a wide variety of environments make them ideal for studying both organismic and molecular evolution. A number of other characteristics make them excellent experimental models for studies in embryology, neurobiology, endocrinology, environmental biology, and other areas. In fact, they have played a critical role in the development of several of these disciplines. Research techniques that enable scientists to make isogenic lines in a single generation, create and maintain mutants, culture cells, and transfer cloned genes into embryos signal an increasing role for fish as experimental models.

http://science.sciencemag.org/content/sci/246/4928/352.full.pdf

Fish as model systems

Growth and stress in fish production

Recently, the global state of marine fisheries and its effects on ecosystems have received much scientific (and public) scrutiny. There is little doubt that global limits to exploitation have been reached and that recovery of depleted stocks must become a cornerstone of fisheries management. Yet, current trends appear to be diverging between well-assessed regions showing stabilization of fish biomass and other regions continuing to decline. This divergence can be explained by improved controls on exploitation rates in several wealthy countries, but low management capacity elsewhere. Here, we identify an urgent need to direct priorities towards ‘fisheries-conservation hotspots' of increasing exploitation rates, high biodiversity, and poor management capacity, and conclude that the future of fish depends, at least in part, on redoubling science, co-management and conservation efforts in those regions.

http://people.uncw.edu/scharff/courses/458/Discussion%20articles/Worm%20and%20Branch%202012%20-%20future%20of%20fish.pdf

The future of fish

The metallothionein-human growth hormone fusion gene (MThGH), constructed by fusing the mouse metallothionein promoter with the human growth hormone gene, was microinjected into the cytoplasm of one-cell embryos of channel catfish Ictalurus punctatus. The 3-week-old fish that developed were analyzed for integrated copies of the MThGH gene. Two of 10 animals contained MThGH sequences that comigrated with genomic DNA of high molecular weight in southern blots. The MThGH sequences were organized in head-to-tail tandem arrays that are characteristic of foreign genes integrated into recipient cell genomes. These data strongly suggest that the MThGH genes are stably integrated into chromosomal DNA, and that transgenic channel catfish can be generated by cytoplasmic injection of early embryos.

Janine Askins

Papers

Transfer of the Metallothionein-Human Growth Hormone Fusion Gene into Channel Catfish