Applications of Gene Technology

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11 Δεκ 2012 (πριν από 4 χρόνια και 8 μήνες)

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Applications of gene technology


Useful applications that are currently used or likely to be used in the near future:




human hormones (e.g. insulin and growth hormone) derived from transgenic
bacteria and used for treating e.g. diabetes and pituitary dwarf
ism.



the genetic engineering of crop plants to increase productivity, disease resistance
or herbicide resistance.



human proteins secreted in milk by transgenic sheep, and used to treat
emphysema.



farm animals engineered to be more fertile, productive and d
isease resistant.



human cell culture for the production of cell products such as vaccines and blood
clotting factors.



human tissue culture for the supply of cells to repair damage (e.g. for skin
grafts), and in attempts to treat Parkinson’s disease by impl
anting embryonic
neural cells in the damaged area of the patient’s brain.



detection of genetic disease early in foetal life, leaving open the possibility of
abortion.



in vitro fertilisation and pre
-
implantation diagnosis of genetic defects.



correction of g
enetic disorders by gene therapy, involving the introduction of
autosomal genes in the treatment of life threatening diseases such as CF.


Production of transformed microorganisms


One of the earliest applications of the techniques of genetic engineering w
as in the
production of bacteria containing human genes, or genes taken from other
eukaryotes. These transformed bacteria are cultured in fermenters, producing large
quantities of protein which is then extracted and purified.


Insulin for the treatment of

diabetics used to be produced from animals, but this
could lead to allergic reactions in patients. Genetically engineered bacteria have had
the gene for insulin inserted into them and therefore produce human insulin which
does not have this problem.


Hum
an growth hormone is used to treat dwarfism


regular injections can allow
children to reach a near
-
normal height. This used to be collected from donated
pituitary glands, which only yielded a very small supply and lead to some problems with
infection. H
uman growth hormone is now produced by genetically engineered
bacteria.


A strain of
Escherichia coli

is commonly used. This is a mutant form which can only
survive in laboratory conditions, to prevent possible escape of the bacteria which
could cause har
m to humans.


Yeast is also often used for genetic engineering, as like bacteria it has plasmids. It
has been genetically engineered to produce human interferon (a protein of the
immune system that protects against viral infection).


Genetically modified
animals


It is much more difficult to manipulate genes in eukaryotes, for several reasons:




Eukaryotes do not have plasmids (exception = yeast).



Eukaryotes are diploid


so two alleles for each gene must be engineered into the
nucleus.



Transcription of euk
aryotic DNA to mRNA is much more complicated.



It is difficult for vectors to penetrate plant cell walls.


“Transgenic” or genetically modified animals have genetic material that has been
artificially introduced from another organism. Ways to do this are:




Transferred genes may be directly injected into cells.



Genes are incorporated into tiny particles and bombarded into cells at high speed.



Electrical pulses are applied to the cell membrane to make temporary holes
through which genes can be introduced (ele
ctroporation).


Transgenic sheep


Transgenic sheep have been successfully engineered to yield rare and expensive
human proteins in their milk. These may be useful as medicines. One example is the
production of a human blood protein called alpha
-
1
-
antitry
psin (AAT). This protein
preserves the vital elasticity of our lungs, and is used to treat patients with
emphysema and cystic fibrosis.


The human gene for AAT production has been identified, isolated and cloned into
sheep, together with a promoter gene f
or milk production. Consequently the sheep’s
mammary glands produce the human protein and secrete it in their milk. AAT is made
available for use with patients.


Transgenic plants


Many commercially valuable plant species have been genetically engineered
, including
cotton, tobacco, oilseed rape, maize, potatoes, soya and tomatoes. The improvements
achieved include:




tolerance to herbicides: if a crop plant can inactivate a weedkiller, then weeds can
be killed without harming the crop plants.



resistance t
o insect pests: the crop plant tissue contains a toxin lethal to insects
but harmless to other animal species.



resistance to viral disease in the crop plant.


Gene therapy


Genetic diseases are conditions that can be inherited, and which are caused by a
sp
ecific defect in a gene. Such diseases affect about 1
-
2% of the human population.
Common genetic diseases include cystic fibrosis, sickle cell anaemia and haemophilia,
which arise from a mutation involving a single gene.


The idea behind gene therapy i
s that it may be possible to clone a healthy copy of the
affected genes and use them to replace the defective copy in affected individuals.


Theoretically, genes could be added into germ cells (eggs or sperms) or into body
cells (somatic cells).



Gene t
herapy has concentrated on disorders caused by a single gene. The healthy
gene has to be located, isolated and cloned. Target cells in the body need to be
robust enough to survive while a sample is withdrawn, cultured, modified genetically,
and then ret
urned to the body. They must then survive for a substantial period
whilst the healthy gene is expressed.


Gene therapy for cystic fibrosis


The mutant allele that causes cystic fibrosis is recessive, and found on chromosome
7. It codes for a transmembran
e regulator protein called CFTR which is found in
epithelial cells. CFTR functions as a pump, transporting chloride ions across
membranes. Water follows the ions, keeping the epithelia smooth and moist.


In CF patients, the protein has one missing amin
o acid, so does not function properly,
leading to the symptoms of CF. The epithelia remain dry, and a thick, sticky mucus
builds up. The effects are felt in the pancreas (secretion of digestive juices) and the
sweat glands (salty sweat is formed). But th
e life
-
threatening consequences are in
the lungs, which may become blocked by mucus and are prone to infection.


Techniques that could be used to introduce healthy CFTR genes into lung epithelial
cells include:




Use of a harmless virus into which the CFTR
gene has been inserted.




Wrapping the gene in lipid molecules that can pass through the membranes of lung
cells. These tiny droplets are called liposomes, and are delivered by aerosol spray.
In trials the treatment seems effective, but it lasts only unti
l the epithelial cells
are routinely replaced. The treatment has to be regularly repeated. The cure can
only be more permanent when it is targeted on the cells that make epithelial cells.


Issues raised by genetic engineering




A new gene, on insertion, m
ay disrupt normal gene function. For example, it could
switch on cancer.




A potentially dangerous microorganism with a new gene may become a dangerous
pathogen if it “escaped” from the laboratory.




Some techniques involve inserting genes for antibiotic re
sistance into bacteria.




The recombinant DNA might get into other organisms; for instance, herbicide
resistance might be transferred to a “weed” species.




Some people may feel that genetic engineering is “tampering with nature”.




Possible suffering of tran
sgenic animals, and those that are experimented on in
trialling new technology.




Genetic engineering is a costly technology that is mostly beneficial to the health
and life expectancy of people of developed nations. If the funds made available
for genetic

engineering were diverted to solve more basic problems of housing,
health, employment and nutrition of the poor worldwide, would the money not
benefit more people?