© 2001 ENDANG
TRI MARGAWATI
Posted 2
June 2001 [rudyct]
Science
Philosophy Student Paper (PPs 702)
Graduate School, Institut Pertanian Bogor
Indonesia.
Instructors:
Prof
Ir Rudy C Tarumingkeng, MF, PhD (Principal)
Prof
Ir Zahrial Coto, MSc. PhD
CONTRIBUTIONS OF
TRANSGENIC ANIMALS
TO HUMAN WELFARE
ENDANG
TRI MARGAWATI
P
04600013/PTK
E-mail:
endangtri@hotmail.com
PREFACE
Nowadays, research in molecular biology has developed
rapidly. It seems that molecular approaches with basic research in agriculture
and medicine are interested to get more benefits in our lives. On this
opportunity, Author presented a paper that relates to the molecular field with
a topic of Contributions of
Transgenic Animals to Human Welfare. The chosen topic may be too compromise for our regular
community but this spectacular progress in the world is necessary to be followed
for some reasons.
This paper was
composed merely on reference sources. As stated on the topic, this paper
elucidated the basic understanding in transgenic animal with the methods of
producing the transgenic animals and their applications in agriculture,
medicine and industry. This paper is an individual paper as a part of tasks in
attending a subject of Introduction to Philosophic Science (PPS 702).
I am deeply
grateful to Professors Rudy C. Tarumingkeng, PhD and Zahrial Coto, PhD. for
their knowledge given in our Science Phlilosophy. I also appreciate their
valuable time in organizing the lectures and providing extra knowledge at
different fields of Science through electronic mail. I hope this piece of work
will give benefits to readers who have related interest in molecular biology.
Bogor,
1st June 2001
ABSTRACT
Since the discovery of DNA molecule structure by Watson
and Crick in 1953 study in molecular biology
studies haves inceased greatly. Consequenly, molecular techniques have
developed rapidly which involve DNA recombinant, genetic cloning and the
analysis of gene expression. Combination of these techniques and transfer of
recombinant genes into living cells of fertilized eggs will produce transgenic
animals. Basically, there are three methods of producing transgenic animals,
i.e DNA microinjection,
retrovirus-mediated gene transfer and embryonic stem cell-mediated gene
transfer. Gene transfer by microinjection is a predominant method in producing
transgenic farm animals.
While on one hand argumentation on
transgenic animals or transgenic products continue among the general community,
on the other hand, their applications to human welfare should be considered as
a positive contribution. The contribution mainly involves three areas i.e,
agricultural, medical and industrial sectors. For examples: in animal farm
breeding, producing transgenic animal can be focused on specific economic
traits. Recently human proteins can be produced in the milk of transgenic sheep
or cattle. In medical and industrial sectors, drugs and enzymes can be produced
in a large scale from transgenic microorganisms or transgenic animals. More
profound report was regarding transplant organs, called Xenotransplantation
that can be supplied from transgenic animal models. Extraordinary finding was
gene therapy in very serious diseases, i.e., creating new blood vessels into heart muscle to
prevent from bypass surgery , or releasing clogged vessel to prevent from leg
amputations by injecting the genes muscularly. In the future, study in
producing transgenic animals will cover wider species and wider human diseases.
INTRODUCTION
Since structure of
DNA molecule was discovered by Watson and Crick in 1953, research in molecular
biology including DNA recombinant, manipulation of DNA and RNA has
improved from time to time. As the
impact of the progresses, many breakthroughs could be made through molecular
research to get more usefulness to human welfare.
As stated by BOYD and SAMID
(1993), technology in molecular biology combines techniques and expertise from
biochemistry, genetics, cell biology, developmental biology and microbiology to
construct an umbrella of disciplines that provides the tools and concepts
necessary to create transgenic animal.
In biotechnology area, transgenic
animals are just one in a series of developments. The creation of transgenic
animals is resulting in a shift from the
use of higher order species to lower order species, and is also affecting the
numbers of animal used. An example of the replacement of higher species by
lower species is the possibility to develop disease models in mice rather than
using dogs or non-human primates.
Transgenic animal
has been pioneered in mice, transgenic mice have been successfully delivered to
born in 1980 (GORDON et al., 1980;
BRINSTER et al., 1981). A few years
later, the results in other animals have been reported in rabbits, pigs, sheep
and cattle (HAMMER et al., 1985;
PURSEL et al., 1987; REXROAD et al., 1989 and ROSCHLAU et al., 1989).
There are many terminologies or definitions regarding Transgenic Animal. One of them has been drawn from FELASA
(September 1992, revised in February 1995). Term of a transgenic animal refers
to “an animal in which there has been a deliberate modification of the genome (the material responsible for
inherited characteristics)”. In World Book 2000, transgenic animal is also
termed as an animal that was engineered to carry genes from other species (http://www.worldbook.com/fun/bth/cloning/html/uses/html).
Why it should be transgenic animal for human welfare ? There
are at least two reasons for it. These are production efficiency of farm
animals (1), and Molecular farming using livestock to produce medicines, human
proteins and tissues for transplant to humans.
The purpose of this
paper is to provide an understanding of transgenic animals that recently is
profound issued in scientific and general community. On the other hand,
usefulness of transgenic animals to mankind has not been elucidated. All
information prepared in this paper was drawn from references. This paper was
prepared to fulfill requirements in attending a subject of Introduction to
Philosophic Science (PPS 702). Therefore, the paper was presented with basic
philosophy of Ontology, Epistemology, Axiology and Teleology which
elucidating why transgenic animal is exist and what it is, how to create the
transgenic animal, the benefits of transgenic animals and position of
transgenic animals in the future, respectively.
METHODS OF PRODUCING TRANSGENIC ANIMALS
The principle of
producing transgenic animal is introducing foreign DNA into the animal, using
recombinant DNA technology, it must be transmitted into germ line, so that
every cell, including germ cells of the animal contain the same modified
genetic material (http://www.ucalgary.ca/~browder/transgenic.html).
Before elucidating
the methods of producing transgenic animal, it is necessary to describe terms
of transgene and transgenic that relates to the producing transgenic animals. A
simple term of a transgene is described as transferred of constructed gene into
the animal genome. The coded protein that produced by transgene is the
transgenic product and animals that contain transgenes are transgenic. Genetic animals are therefore created when animals or
offspring, transgenic lines or populations bring the transgenes materials.
There are at least 3 methods in
creation of transgenic animals:
a.
DNA microinjection
b.
Retrovirus-mediated gene transfer
c.
Embryonic stem cell-mediated gene transfer
1.
DNA microinjection
The first
successful of gene transfer using DNA microinjection method was reported in
mouse (GORDON et al., 1980). This
method was reported as one of the first methods that proved to be effective in
mammals (GORDON and RUDDLE, 1981). A method of the DNA microinjection consists
of the direct microinjection of a desired gene construct (of a single gene or a
combination of genes) in plasmid or in cosmids, from another member of the same
species or from a different species into the pronucleus of a zygote (http://www.fao.org/ag/aga/agap/war/warall/ul200b/ul200b04.htm). The manipulated
fertilized egg is then transferred to the recipient female. Before transferring
to the recipient female, the manipulated egg needs to be cultured in vitro to meet an appropriate stage of
embryo. The insertion of DNA is a random process, it could be over- or
under-expression of certain genes or to the expression of genes entirely new to
the animal species (CCAC, 1997). Therefore, the offspring born from introduced
gene animal needs to be investigated whether they have integrated the gene
construct. Methods of ‘Southern blot’ or ‘Dot blot’ hybridization are performed
to ascertain the constructed gene. Since the success of producing transgenic
animals is very low (2-3%), it would be efficient if multiply of transgenic
animals can be made by cloning technique.
In farm animals, DNA microinjection is the predominant method
used to transfer gene into their genome. The method used in farm animals is the
same as in a mouse, a slightly different technique is merely in making the
pronuclei structure visible by using centrifugation than by hyaluronidase
treatment as stated in a mouse.
2. Retrovirus-mediated gene transfer
Retroviruses are commonly used as vectors to transfer genetic
material into the host cell. The genetic material is subsequently integrated
into the genome of the host cell. The host cell can fold in producing
transgenic products (e.g., insulin). Transmission of transgene is possible only
if the retroviruses integrate into some of the germ cells. In 1974, the first
time was shown that inserted DNA has been found in the cells of adult mice
after the blastocoel of mouse blastocyst had been injected by SV40 DNA
(JAENISCH, 1974; JAENISCH and MINTZ, 1974). It was also reported that the
transgene of the Mo-Mulv-provirus DNA has integrated into genome and passed on
to offspring and built up to stable lines (JAENISCH, 1976; STUHLMANN et al., 1981).
The success of this method in terms of live birth of animal
containing the transgene is low. The expression of the transgene needs to be
tested. When the transgene integrated into the germ cells, so called germ line
chimeras are then inbred for 10 to 20 generations until the homozygous
transgenic animals are established and the transgene is present in every cell
(revealed from CCAC, 1997).
3. Embryonic stem cell-mediated gene
transfer
This method involves prior insertion of the desired DNA sequence
by homologous recombination into an in
vitro culture of embryonic stem (ES) cells. Stem cells are undifferentiated
cells that have the potential to differentiate into any type of cells (somatic
or germ cells) and to give rise development. Cells containing the desired DNA
are incorporated (through aggregation or injection) into an embryo. The stem
cell is used as a vehicle to introduce new genes. An animal resulted by this
method is so called a chimeric animal. This method has been adapted from CCAC
(1997) and http://www.fao.org/ag/aga/agap/war/warall/ul200b/ul200b04.htm.
In 1989, generation of transgenic mice and pigs was reported by
using a technique of sperm-mediated gene transfer (LAVITRANO et al., 1989; GANDOLFI et al., 1989). This method was quite
simple and efficient.
APPLICATIONS OF TRANSGENIC
ANIMALS
Several benefits
can be picked up from the transgenic animals. It can be classified into three
fields: Farm animal (1); Pharmaceutics and medicines (2) and Industry (3).
1. Farm animal
Application
a.
In Breeding
Long before
technologies in molecular biology were discovered, selective breeding was
performed by selecting animals which have enhancement of chosen traits (e.g.,
increased milk production, high growth rate).
Once research in molecular biology has developed, a certain gene that
responsible to chosen trait even foreign gene can be constructed then
transferred to the generation or pedigree. These pedigrees that bring the
transgene can be multiplied by cloning. Therefore, by using transgenic animals,
the breeding program in farm animals can be performed efficiently both in number of animals and
shorten interval time.
b.
Quality of animal products
In the past, using
growth hormones for increasing the growth of animals was to be a problem, it
was presumed that residue of hormones remain there. At present, using
transgenic animals that bring transgene expression on tissue and developmental
stage specificity is very important for a successful in industrial application.
It can be understood because transgenic animals
will perform a misdirected expression of bovine growth factor (LEE et
al., 1997). Transgenic animal that responsible for increasing growth and body
composition has been conducted in pigs (HAMMER et al., 1985; VIZE et al., 1987) and in sheep (WARD et al., 1986).
A model of
reducing lactose contents of milk has been made in the milk of transgenic sheep
and cattle (MERCIER, 1987). This milk is consumed by people who suffering from lactose
intolerance.
Gene transfer in
wool growth was also undertaken to create transgenic sheep (WARD et al., 1986).
c. Disease
resistance
A very limited
number of genes responsible to resistance of diseases in domestic animals.
However, attempts have been made to produce influenza-resistant pigs through
the transfer of three Mx-gene constructs (http://www.fao.org/ag/aga/agap/war/warall/ul200b/ul200b04.htm)
2. Pharmaceutical
and Medical Applications
a. Xenotransplantation
The need of
transplantation of hearts and kidneys has become routinely in past 20 years
ago, about 5000 suitable organs were needed each year in United Kingdom and
many patients died (http://www.rl.bbsrc.ac.uk/cloning/benefits.html). It was also
reported that thousands of patients die every year before a replacement heart,
liver or kidney becomes available. At present, it is possible to produce transgenic
pigs that provide as sources of transplant organs, called xenotransplantation
or xenogenic transplantation (HOAGLAND et al., 1997). At present, production of
transgenic pigs have been directed to cope with the rejection of transplanted
organs by adding human proteins that prevent immediate rejection of the
transplanted heart or kidney (http://www.rl.bbsrc.ac.uk/cloning/benefits.html).
b. Cell Therapy
Intact cells are already used to treat patients suffering from a
number of diseases including Leukemia and Parkinson’s disease (http://www.rl.bbsrc.ac.uk/cloning/benefits.html).
c. Human proteins
It has been possible to produce valuable proteins on a large
scale in the milk of transgenic animals. a-lactalbumin: PPL Therapeutics (Blacksburg, VA and Edinburgh, UK) in
collaboration with Wyeth-Ayerst (Philadelphia) has announced the first
expression data for the production of human proteins in the milk of transgenic
cows (E.T.S., 1997; BLACKSBURG and
WYETH-AVERST. 1997). First transgenic cow, Rosie, has born, with production of
2.4 g of human protein a-lactalbumin per
milk, compared with 2.5-2.7 g found in human milk (E.T.S.,1997). This
transgenic milk is more nutritionally balanced than bovine milk, and could be
given to babies or the elderly with special nutrition or digestive needs
(E.T.S.,1997; http://www.rl.bbsrc.ac.uk/cloning/benefits.html and http://www.ucalgary.ca/UofC/eduweb/virtualembryo/cloning.html).
Phenylalanine-free
form of b-lactalbumin: PPL therapeutics
has also reported that the second transgenic cow will be created to produce
phenylalanine-free form of a-lactalbumin for
use as a nutritional supplement in people suffering from phenylketonuria (PKU),
a debilitating disease or down syndrome disease which phenylalaline cannot be
broken down into tyrocine due to lack of a certain gene for its synthesis
(E.T.S., 1997 and NOOR, 1996). Cattle
transgenic for phenylalanine are now being investigated by PPL therapeutics, Edinburgh.
There are some reports of progressing in recovery of serious
diseases by gene therapies (extracted from E.T.S., 1998). These are creating
new blood vessels into heart of 60 years old man at New York Hospital. Another
gene therapy has also been reported in a group of patients who have been
hopelessly blocked blood vessels in their legs and have to be amputated. By
intra muscular injecting of naked DNA strands coding for human vascular
endothelial growth factor (VEGF), it has saved their legs.
3. Industrial
Application
Enzyme products:
In mid-1998, most
genetically engineered proteins were being manufactured in bioreactors so that
billions of genetically modified microorganisms produce a wide variety of
proteins (http://www.worldbook.com/fun/bth/cloning/html/uses/html).
These proteins can produce enzymes for use to speed up industrial chemical
reactions.
CONCLUSIONS
In the future,
application of the transgenic animals techniques will be more important since
transgenic animals could provide a large scale of agriculture, medical and
industry products. These products will give more benefits to those respective
industrial sectors. agricultural
Nuclear transfer
provides a reliable way of producing transgenic animals by reducing the number
of animals needed to establish each transgenic line. It only needs to reserve
cloned embryos or cloned germ cells (sperm or eggs) that has been
genetically-modified instead of maintaining the animals.
The need of
transplant organs (xenotransplantation) can be supplied from transgenic models,
investigations to improve the acceptance of implanted organs are being refined.
In the long term, the number of animals used to study human diseases is reduced since a greater specificity of the transgenic models developed. On the other hand, a wider range of diseases could be investigated since methods in creating transgenic models have been improved from time to time. The use of some species may be wider.
All above brilliant progresses in Science and Technology need to
be followed with the deepest of wishes that all developments are for human
welfare to live in peace. It seems that responsibility, moral, ethic and
religion of scientists play an important role in the application of their
discoveries.
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