Genetically Modified Organism (GMO)- Bacteria, Plants, Animals

A Genetically Modified Organism (GMO) is defined as a genetically modified organism that could be a plant, microbe, or animal whose genome is altered using traditional methods such as selective breeding or advanced genetic methods such as reproductive cloning and recombinant DNA technology, in order to produce an offspring with a selective desired trait.

Genetically Modified Organism (GMO)- Bacteria, Plants, Animals
Genetically Modified Organism (GMO)- Bacteria, Plants, Animals

What is a Genetically Modified Organism (GMO)?

  • the DNA of any plant, animal, or microbe is altered using genetic engineering
  • conventional methods: selective breeding or cross-breeding,
  • disadvantages: often produces mixed results with many undesirable traits showing with the desired traits. 
  • Advanced method: genetic engineering
  • Advantage: produce only desired trait in an organism without any undesirable trait

History of Genetically Modified Organism (GMO)

  • 1973- StanleyCohen and HerbertBoyer
    • the technique of cloning DNA
    • that allowed gene manipulation and transferee into other species.
  • 1982- first transgenic mice are developed using microinjection into the fertilized mouse eggs and it has the promoter for rat growth hormone.
  • 1988- first tobacco plan is successfully created 

Basic Procedure of Transgenesis

The process includes a foreign gene that is added to the host organism and this gene can be derived from an unrelated species than a host organism. Steps involve:

  1. Elimination (e.g., knock out animals): specific portion in the host organism is knocked out to replace it with the desired gene.
  2. Introduction of foreign DNA: then, introducing the desired gene from even an unrelated species 
  3. Production of transgenic organism: it is the result of the successful introduction of foreign DNA into a host organism know known as a transgenic organism. And the introduction of genes is usually carried out in the early stages of the development of the host organism.

Genetically Modified Bacteria

E. coli for insulin production

  • Transformation: the process of introduction of foreign DNA into a cell, 
  • Requires a competent cell, which is introduced in E. coli using calcium chloride.
  • After the treatment, foreign DNA becomes capable of introduction into the competent cell and thus later integrate into the genome. 
  • Disadvantage: less efficient, require selection marker
  • Advantage: easy to perform, cheap
  • Herbert and Boyer in 1978 used the same competent cell of E. coli to produce insulin which is used to cure diabetic patients.
Transformation of E. coli cell
Transformation of E. coli cell

Genetically Modified Plants/Crops

  • By the students of the university in Washington, in the early 1980s.
  • Have beneficial traits like resistance to a pest, virus, and herbicides, enhanced nutritional value, and resistance to extreme environmental conditions such as salinity, high temperature, extreme pollution, drought, etc.
  • Some transgenic food items in current use such as corn, tomato,  potato, canola, papaya, soybeans, etc.

Process of development of transgenic plant

Agrobacterium tumefaciens

  • the bacterium that causes the formation of large tumors in dicotyledon plants. 
  • Using Ti plasmid and this plasmid is transmitted to the infected plant and causes a tumor.
  • This property of tumor-inducing is used by scientists to transfer the desired gene into the host cell by removing the infectious part of the plasmid and retaining only its capability of it to transfer into the infected cell. 
  • Disadvantage:  bacterium is species-specific.
  • Advantages: increased copy number, controlled site of integration, cheap.
Agrobacterium-Mediated Transformation
Agrobacterium-Mediated Transformation

Gene Gun

  • the advantage over the A. tumefaciens: is not species-specific, 
  • the coating of the desirable DNA fragment which is inserted with tiny gold or tungsten particles and shot into the cell’s cytoplasm. Thus, it integrates into the chromosome and permanent transfection can be achieved.

Other less common approaches for transgenesis in plants are infiltration, electroporation of cells and tissues, pollen-tube pathway, electrophoresis of embryos, microinjection, etc. E.g., in 1985, electroporation was used to transfer foreign genes to make transgenic tobacco and maize. 

Examples of Genetically Modified Plants/Crops

Bt-cotton

  • Bacillus thuringiensis is a soil bacterium 
  • that contains endotoxin protein 
  • used in the generation of Bt cotton
  • Agrobacterium tumefaciens approach of transfection is used. 
  • With the introduction of endotoxin protein, transgenic cotton becomes resistant to herbicides and insecticides. 
  • The gene is transferred is Cry 1 AC into the promoter  CaMV of A. tumefaciens

Golden rice

  • By Igno portrukus and peter Beyer 
  • using a multigene biochemical pathway from genome integration. 
  • has vitamin A which is produced from beta-carotene that is metabolized by humans and used in the further formation of retinoic acid. 
  • The golden color of golden rice is due to the presence of beta carotene incorporated in it. 

Bt-corn

  • In the US, it is the most widely used crop, that is produced by GMO
  • Bt-corn is herbicide resistance and pest resistance
  • Used for consumption as feed livestock for cows, chickens, poultry, etc
  • It is modified to produce a protein that is toxic to pests but is consumable to humans and animals, thus it reduces to need to add additional herbicides or pesticides.

GMO soybeans

  • In the US, most soy grown is GMO soy.
  • Soybean oil and feed livestock are major derivatives of GMO soy.
  • Used as an ingredient in the form of lecithin, emulsifiers, and proteins in processed foods.

GMO potatoes

  • Few potatoes are modified to resist pests and insects while some are to resist the browning of potato when cut with a knife. 
  • It helps in reducing the wastage of potatoes because people tend to confuse the browning of potatoes with its spoilage.

Genetically modified animals

Mice

  • incorporation of the additional gene into the genome of mice: transgenic or knockout mice. 
  • transgenic mice: contain inserts at any site in their genome, nonhomologous recombination
  • knockout mice: have a specific site of recombination, require homologous recombination
  • The desired gene insert using: microinjection or viral vector
  • A positive selection marker is required: to identify successful transformation
  • Later, the modified embryonic stem cells were transferred into a female animal for gestation through injection into a blastocyst.
Transgenic-Mice-Production-Microinjection
Figure: The process of production of transgenic mice.

Zebrafish

  • Developed in 2003
  • Used as an indicator of water pollution
  • When the water pollution exceeds the optimal level, GMO zebrafish produce fluorescent under UV light
  • In normal lighting, they are bright red and under UV, they produce fluorescent.

Pigs

  • Produce for consumption by people with meat allergies, for the production of drugs, and to provide organs and tissue for human transplants.
  • Approved by US  FDA for both medical and consumption purposes.
  • Produced by the company known as Revivicor.

Cows

  • Engineered to have a thin hair coat known as a slick coat and have better chances of survival in a warmer climate.
  • Engineered using CRISPR-Cas gene-editing tool by a firm called Acceligen.

Genetically modified viruses

Oncolytic viruses

  • Traditional ways to treat cancer such as radiation have major disadvantages as it directly targets the cancer cells, leaving other nearby normal cells vulnerable to radiation, but with the use of immunotherapy, a person’s immune system can be strengthened to target the cancer cell by itself.
  • For that very purpose, genetically engineered oncolytic viruses are created in order to increase the host immune response.
  • Herpes simplex virus, reovirus, and vaccinia virus are some examples that can be engineered as oncolytic viruses.
  • Cancer cells are induced in order to express the proinflammatory cytokines, promote immunogenic death of cancer cells, and increase antigenic presentation by cancer cells.
  • E g: melanoma cancer can be treated with DNA manipulation of lentivirus.

Adenoviruses

  • Used for producing vaccines, gene therapy, and cancer cell therapy.
  • Mostly used adenoviruses are AD5.
  • They are highly immunogenic and can initiate both innate and adaptive immunity.
  • Vaccines produced can be administered orally as well, which are highly effective for respiratory disorders.
  • AD5-based vectors can target kuffer cells in livers, macrophages, neutrophils, RBCs, and platelets.
  • There are two types of adenoviruses, replication-defective, and replication-competent.
  • RD type can be used best to produce vaccine while RC type is an oncolytic virus.
  • E g, the HIV vaccine known as HVTN is in clinical trials, using the AD5 RD adenovirus vector.

Regulations on Genetically Modified Organisms (GMO)

Labeling of food

  • It provides identity to the food, the amount in the package, cooking instructions, serving size, safety concerns (like allergens), and nutritional facts.
  • People can judge what’s in their food and decide whether they want to consume it or not, just by looking at the label
  • So, a label should not be misleading
  • It must be truthful
  • It should give complete information
  • Regulation by food and drug administration of US and US department of agriculture.

The regulation of GMO crops in the US is divided among three nodal US regulating agencies:

  1. EPA: stands for an environmental protection agency
  • It looks upon the regulation of biopesticides under the federal insecticide, fungicide and rodenticide act (FIFRA)
  1. FDA: stands for food and drug administration of the US
  • Regulated the safety of GM crops that are consumed by humans and animals
  1. US department of agriculture
  • Regulate the consultative process which is a voluntary consultative process with crop development before a genetically modified crop is marketed.

Risk related to production and consumption of GMO

Risk for the person: can be divided according to the type of food

Toxic food

  • Food poisoning

Non-toxic food

  • Non-immune mediated problems like auto-intoxication, anti-nutrients, food tolerance
  • Immune-mediated responses such as food allergy

Risk to the environment

  • Extinction of existing species of animals and plants
  • Interfere with environmental balance including gene transfer, uncontrolled spread of transgenic species, etc

Advantages of Genetically Modified Organisms (GMO)

  • Greater yield
  • Better nutrionial values
  • Food has a longer shelf life
  • Because of increased shelf life, it is easy to transport
  • Reduced use of herbicides and pesticides
  • Used in pharmaceutics, to produce vaccines, insulins, and disease treatment
  • Transgenic mice have wide application in research 
  • Higher yield of crops
  • The desired trait in crops can be monitored and controlled

Disadvantages of Genetically Modified Organisms (GMO)

  • Associated ethical issue
  • Can be complex to be understood for farmers
  • Can introduce antibiotic resistance
  • More legal liabilities for farmers growing GMO
  • No independent research can be done
  • Genes pass into other plants species
  • Lack of awareness among consumers

References

  1. Andrea Paparini, Vincenzo Romano-Spica, Public health issues related with the consumption of food obtained from genetically modified organisms, Biotechnology Annual Review, Elsevier, Volume 10, 2004, Pages 85-122, ISSN 1387-2656, ISBN 9780444517494, https://doi.org/10.1016/S1387-2656(04)10004-5.
  2. Liggett, S. Genetically modified mouse models for pharmacogenomic research. Nat Rev Genet 5, 657–663 (2004). https://doi.org/10.1038/nrg1429
  3. Gasson, M., Burke, D. Scientific perspectives on regulating the safety of genetically modified foods. Nat Rev Genet 2, 217–222 (2001). https://doi.org/10.1038/35056066
  4. Baranski, Marci, “Golden Rice”. Embryo Project Encyclopedia (2013-09-17). ISSN: 1940-5030 http://embryo.asu.edu/handle/10776/6275.
  5. J Food Sci Technol. 2013 Dec; 50(6): 1035–1046. 2012 Dec 19. doi: 10.1007/s13197-012-0899-1
  6. Rafferty SA, Quinn TA. A beginner’s guide to understanding and implementing the genetic modification of zebrafish. Prog Biophys Mol Biol. 2018 Oct;138:3-19. DOI: 10.1016/j.pbiomolbio.2018.07.005. Epub 2018 Jul 19. PMID: 30032905.
  7. Stephenson JR. Genetically modified viruses: vaccines by design. Curr Pharm Biotechnol. 2001 Mar;2(1):47-76. doi: 10.2174/1389201013378815. PMID: 11482348.
  8. https://www.nationalgeographic.org/encyclopedia/genetically-modified-organisms/
  9. https://bio.libretexts.org/Bookshelves/Biochemistry/Supplemental_Modules_(Biochemistry)/6.Lab_Notes_Part_2/6.1%3A_Genetic_Transformation(using_bacteria_and_the_pGLO_plasmid)
  10. https://www.fda.gov/food/agricultural-biotechnology/how-gmo-crops-impact-our-world
  11. https://vittana.org/12-advantages-and-disadvantages-of-genetically-modified-foods
  12. https://www.fooddive.com/news/fda-approves-gmo-cattle-for-food/620061/
  13. https://www.cicr.org.in/pdf/transgenic_bt_cotton.pdf
  14. https://gmo.uconn.edu/topics/gmo-regulation

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