Engineering case studies -2: Golden Rice
Vitamin A deficiency - Many people a year become blind after a lack of vitamin A in their diet. Children under 5 and pregnant women are mostly at risk. The poorer populations of many countries where vitamin A is significant reply mainly on rice as their main source of food.
Vitamin A is formed from beta carotene in the human gut and comes from animal courses in the diet. If vegetarian, the intake of beta carotene; precursor, is converted to Vitamin A in the gut. For the adsorption of vitamin A the diet had to include lipids as vitamin is fat soluble.
Rise has been engineered to be rich in beta carotene. Plants naturally produce beta carotene, but the rice parts do not have the beta carotene gene switched on. When beta carotene accumulates in the endosperm results in golden coloured rice.
Engineering Golden Rice - The enzymes for the pathway needed to produce beta carotene is already present in the endosperm. The insertion of two genes into the rice genome would activate the endosperm cells. Phytoene synthetase; extracted from daffodil plants and Crt1 enzyme; gene extracted from siol bacterium. These genes were inserted into the rice genome near a promoter sequence that switches on endosperm development. They were expressed as the endosperm grew.
Engineering case studies -2: Golden Rice
Further developments -
- Cross breeds of natural rice varieties and Golden Rice proved that these hybrids could make 3-4 times as much beta carotene than the original variety. Golden Rice 2 can produce up to 20 times as much as the original plant.
Humanitarian triumph or public relations exercise?
- Farmers of golden rice do not have to pay a license fee so they can keep and replant the seeds. People have targetted the company to gain public acceptance of genetically modified crops.
- Using these crops will reduce the biodiversity and the GM rice could breed with wild types of rice contaminating populations.
- However, the rice still does provide many people with a source of vitamin A that no one else has an answer for.
Golden rice is biofortified - it contains higher than normal concentrations of a particular nutrient; beta carotene.
Gene therapy -
- Molecular genetic technology can be used to treat some genetic disorders. If we can get the working copy of the gene into cells where the dysfunctional copy of the gene are being transcribed, the working copy can be expressed and symptoms of that genetic disorder may disappear.
- The Human Genome Project has identified the possible use of interferance RNA that can silence genes by binding to mRNA; used to stop the replication of cytomegalovirus in AIDS patients.
Somatic cell gene therapy - use of specialised cells that have few active producing proteins that are not relevant to that cells function.
- Gene therapy by adding genes (augmentation): Inheritance of faulty alleles leading loss of a function gene product can be engineered by using a functioning copy of the gene in the relevant cells meaning the polypeptide is synthesised and cell function is normal.
- Gene therapy by killing specific cells: Cancers can be treated by removing certain populations of cells. Using techniques to make the cancers express proteins that are vulnerable to attack by the immune system could lead to targeted cancer treatments.
Germline cell gene therapy -
- Each cell of an early embryo is a stem cell. Engineering a gene into the sperm, egg or zygote cells mean that early embryos all contain a copy of the engineered gene. This gene can then function within any cell where the gene is required.
Transgenic animals have been engineered and functioning allele may be passed onto their offspring. This means that in germline cell gene therapy the new function gene is passed on to their offspring. In Somatic cell gene therapy the modifications are not.
Germline cell gene therapy has been stopped by the Clothier committee as they say that the:
- Interferance of a new DNA could make human evolution happen in an unexpected way
- The modifications are morally, ethically and socially wrong.
Somatic cell gene therapy - Germline cell gene therapy
- techniques to get the gene into the location needed are complex - delivery techniques are more straight forward
- treatment is short lived and has to be repeated regularly - all cells from the germline cells contain functioning copy of the alelle.
- difficulties getting the gene into the cell in a functioning state; virus result in immunity of host and liposomes are inefficient - considered unethical to engineer a human embryo incase of unintentional damages.
- genetic manipulations are restricted to the actual patient - genetic manipulations are passed onto the patients children.
Gene therapy for SCID - SCID is when a defective gene for the enzyme adenosine deaminase (ADA) is lacking, and toxic T lymphocytes build up so loss of these cells occur.
A retrovirus is used to get the normal ADA gene into the DNA of cells./ The bone marrow containing T cells is exposed to the retrovirus are viral infection causes the ADA gene to be taken up. The transgenic cells put back in the bone marrow are expressed with functional ADA.
Ethical Issues of Genetic Manipulation
Shortage of transplant organs - Recent advances in understanding the mechanisms of transplant organ rejection means we can consider transplants from other species; xenotransplantation. Engineering pigs as organ donors - Pig organs for xenotransplantation is being developed as they dont produce enough of the enzyme required to not reject the transplant.
- The pigs do have different organ sizes, organ's age more quickly and the natural body temperature for pigs is higher than that of humans.
- Animal welfare groups are against killing pigs to harvest organs. Some religions are against eating pork and disease transfer between humans nd animals exist.
Ethical concerns raised by genetic manipulation - MICROORGANISMS: more widespread antibiotic resistance, contamination of pathogenic microorganisms that have been not been GM'ed. PLANTS: loss of genetic variation, resistance to pesticides etc, change stability of biological communities and food chains, GM plants could be toxic. ANIMALS: welfare issues, religious issues. HUMANS:effects of gene transfer are unpredictable, eliminate disease that keep balance of life and death equal but also enhancing favourable characteristics.