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Published byCaroline Stone Modified over 8 years ago
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Chapter 7/8: Animal Genetic Engineering Methodology and Applications
Transgenic animals created by 2 methods 1) Microinjection of fertilized eggs 2) Transfection and implantation of embryonic stem cells … .(gene knock-outs & Cre-loxP recombination system) Transgenic animals: some examples Transgenic fish: some examples Mammalian Cloning by nuclear transfer
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Establishing transgenic mice by DNA microinjection
Most commonly used method Only 5% or less of the treated eggs become transgenic progeny Need to check mouse pups for DNA (by PCR or Southerns), RNA (by northerns or RT-PCR), and protein (by western or by some specific assay method) Expression will vary in transgenic offspring: due to position effect and copy number
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Creating a transgenic mouse using the DNA microinjection method
See See also And for reporter constructs, see
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Establishing transgenic animals using engineered embryonic stem (ES) cells But what are ES cells?
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Transgenic animals-Engineered embyronic stem cell method (used for gene knockouts) Step 1: Get the ES cells
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Step 2: Genetically engineer the ES cells
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Step 3: Place engineered ES cells into an early embryo (Fig. 19
Step 3: Place engineered ES cells into an early embryo (Fig. 19.4) see
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Transgenic animals-Using Cre-loxP for tissue or time-specific gene knockouts
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Transgenic mice: applications
Transgenic models for Alzheimer disease, amyotrophic lateral sclerosis, Huntington disease, arthritis, muscular dystrophy, tumorigenesis, hypertension, neurodegenerative disorders, endocrinological dysfunction, coronary disease, etc. Using transgenic mice as test systems (e.g., protein [CFTR] secretion into milk, protection against mastitis caused by Staphylococcus aureus using a modified lysostaphin gene) Conditional regulation of gene expression (tetracycline-inducible system) Conditional control of cell death (used to model and study organ failure; involves the organ-specific engineering of a toxin receptor into the mice and then addition of the toxin to kill that organ)
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Another Transgenic mouse application: Marathon Mice
Instead of improving times by fractions of a second, the genetically enhanced “marathon” mice (above, on the treadmill in San Diego) ran twice as far and nearly twice as long as ordinary rodents. The peroxisome proliferator-activated receptor (PPAR-delta) gene was overexpressed in these transgenic mice. For details, see Dr. Ron Evans and one of his genetically engineered “marathon” mice. The enhanced PPAR-delta activity not only increased fat burning, but transformed skeletal muscle fibers, boosting so-called "slow-twitch" muscle fibers, which are fatigue resistant, and reducing 'fast-twitch' fibers, which generate rapid, powerful contractions but fatigue easily.
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Transgenic cattle, sheep, goats, and pigs
Using the mammary gland as a bioreactor (see adjacent figure) Increase casein content in milk Express lactase in milk (to remove lactose) Resistance to bacterial, viral, and parasitic diseases Reduce phosphorous excretion
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Some exogenous proteins that have been expressed in the mammary glands of transgenic animals
Erythropoietin Factor IX Factor VIII Fibrinogen Growth hormone Hemoglobin Insulin Monoclonal antibodies Tissue plasminogen activator (TPA) a1-antitrypsin
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“Enviropigs” Transgenic pigs expressing the phytase gene in their salivary glands The phytase gene was introduced via DNA microinjection and used the parotid secretory protein promoter to specifically drive expression in the salivary glands Phytate is the predominant storage form of phosphorus in plant-based animal feeds (e.g., soybean meal) Pigs and poultry cannot digest phytate and consequently excrete large amounts of phosphorus “Enviro-pigs” excrete 75% less phosphorus EnviropigTM an environmentally friendly breed of pigs that utilizes plant phosphorus efficiently.
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And then there is “transgenic art” with GFP…
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Transgenic fish Genes are introduced into fertilized eggs by DNA microinjection or electroporation No need to implant the embryo; development is external Genetically engineered for more rapid growth using the growth hormone gene (salmon, trout, catfish, tuna, etc.) Genetically engineered for greater disease resistance Genetically engineered to serve as a biosensor for water pollution
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GloFish: http://www.glofish.com/
Where do GloFish® fluorescent zebra fish come from? GloFish® fluorescent zebra fish were originally bred to help detect environmental pollutants. By adding a natural fluorescence gene to the fish, scientists hope to one day quickly and easily determine when our waterways are contaminated. The first step in developing these pollution detecting fish was to create fish that would be fluorescent all the time. It was only recently that scientists realized the public's interest in sharing the benefits of this research. We call this the GloFish® fluorescent fish.
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Transgenic salmon over-expressing GH
Above is a picture showing the respective growths of a GM salmon and a non-GM one at the same age (Credit: Aqua Bounty). But why is this GM fish growing so fast? These GM salmon grow so fast because of a change made to one of the roughly 40,000 genes in their DNA. In normal salmon, the gene that controls the production of growth hormone is activated by light, so the fish generally grow only during the sunny summer months. But by attaching a constitutive "promoter sequence", Aqua Bounty ended up with salmon that make growth hormone all year round.
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Cloning livestock by nuclear transfer (e.g., sheep) “Hello Dolly”
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And now there is pet cloning for a “small” fee…
Nine-week-old "Little Nicky" peers out from her carrying case in Texas. Little Nicky, a cloned cat, was sold to its new owner by Genetic Savings and Clone for $50,000 in December 2004. August 07, 2008 | Bernann McKinney with one of the 5 puppies cloned from Booger, her late pet pit bull. It cost her $50,000. When Booger was diagnosed with cancer, a grief-stricken McKinney sought to have him cloned -- first by the now-defunct Genetic Savings and Clone, and then by South Korean company RNL Bio.
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THE DANGER OF MAMMALIAN CLONING!
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