Creating Transgenic Animals

Like plants, animals can be genetically manipulated to carry genes from unrelated organisms. Traditional methods to create transgenic animals

involve the introduction of engineered transgenes to early embryos.23 This is done in a variety of ways, including infection of embryos with transgene-carrying attenuated retroviruses, microinjection into the pronuclei24 of zygotes, or physically mixing recombinant DNA with embryonic stem cells or sperm (Thieman and Palladino 2012). If taken up by cells, transgenes usually integrate randomly into the genome. This may accidently disrupt another important protein coding or intergenic region within the DNA. Following genetic manipulation, modified embryos are implanted into surrogate mothers for development. Transgenic organisms are identified by the expression of reporters (e.g., green fluorescent protein [GFP]) or molecular screens (e.g., PCR). Collectively, these techniques are error- prone, expensive, and inefficient.

The emergence of CRISPR technology has revolutionized the field of transgenesis. In just a few years, “designer” animals such as miniature pigs (for pets and research) and goats with extra long hair and enhanced musculature (for cashmere and meat) have been created (Ledford 2015a). One Chinese group sparked an international debate when they published the first, rather unsuccessful, account of CRISPR/Cas9 manipulation of human embryos25 in May 2015 (Liang et al. 2015). As a result, an international panel of scientists, hosted by prominent scientific academies,26 declared a voluntary moratorium on the genetic manipulation of inheritable human genes—at least until the “bugs” in the technology can be worked out (Wade 2015).

In the meantime, scientists are developing all kinds of beneficial transgenic animals. On the horizon are hypoallergenic chicken eggs and disease-resistant goats, pigs, cattle, and perhaps even bees (Reardon 2016). GFP-expressing male chickens, hypermuscular cows, and dehorned cattle are all being developed to reduce animal culling and improve animal welfare (Yang et al. 2016b). Since CRISPR is especially good at creating multiple mutations simultaneously—a process called gene stacking— even loftier goals, such as reconstructing the wooly mammoth genome through the manipulation of Indian elephant DNA, are being discussed (Reardon 2016). Researchers are especially enthusiastic about the development of large animal models for the study of human diseases. For example, disease models for Parkinson’s disease are a high priority (Tu et al. 2015; Yang et al. 2016b).

Box 4.4. Meat without livestock

Global meat consumption is expected to double between 1999 and 2050 (Tuomisto and de Mattos 2011). Such a demand cannot be met due to the intense land/water/fuel resource costs and greenhouse gas emissions associated with livestock production. Synthetic meat, made from animal stem cells, is being developed as a potential answer to humane and sustainable meat production (Ghosh 2015). According to one report, synthetic meat requires 7 to 45 percent less energy, 99 percent less land, 82 to 96 percent less water, and emits 78 to 96 percent less greenhouse gases than conventional animal products (Tuomisto and de Mattos 2011). Synthetic meat would also decrease zoonotic diseases by limiting contact between animals and humans (Tuomisto and de Mattos 2011). The first lab-grown beef patty was taste-tested in London in 2013, with mixed reviews (Ghosh 2015). Ongoing design challenges include recreating the complex flavor profiles and texture of real meat. Although the current cost of a five-ounce synthetic beef patty is around $325,000, developers project that this figure will drop dramatically in the near future (Goudarzi 2016). Lab-grown meat is expected to hit the global market around 2020 (Ghosh 2015).

BRIEF SUMMARY

The current industrialized food production system is straining to feed an expanding global population with an increasing appetite for meat. Issues related to insufficient yields, food safety, and product quality arise. Biotechnology can help to address these problems. Specific tools to enhance food safety include biosensors to detect contaminants in tainted foods and livestock genetically modified (GM) or immunized to resist zoonotic disease. Transgenic crops and livestock are created to increase yields, usable farmland, and product quality. Although GM-livestock are not yet widely used, this may change with CRISPR/Cas9 genome editing. Even synthetic meat made from animal stem cells may be a way to mitigate the environmental impact of livestock production.

 
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