Spider silk is truly an amazing material. It is stronger
than almost any other manmade fiber. It is stronger than steel and more elastic
than a rubber band. Its tensile strength is five times that of steel and it can
stretch up to 30% longer than its original length without breaking (Tom Harris,
animals.howstuffworks.com). Because of these amazing qualities, spider silk has
sparked dozens of ideas of new and innovative ways to use it. However, nobody
has had a sufficient amount of spider silk material to conduct full scale tests
of these would-be products. Some possible products include lighter, stronger
bulletproof clothing, artificial skin, better bandages, gentler airbags,
elastic ligaments and better surgical sutures. Figure 1 below shows a spider
weaving its web out of spider silk in the wild. The outermost part of the web
is made by the dragline silk which is the silk that people are most interested
in.
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| Figure 1: A spider weaving its web out of spider silk http://www.popularmechanics.com/cm/popularmechanics/images/mG/Spider-Silk-01-0112-lgn.jpg |
The major silk producing countries in the world include China, India, Uzbekistan, Brazil, Japan, South Korea, Thailand, Vietnam and Iran while the biggest silk consuming countries are USA, Italy, Japan, India, France, China, United Kingdom, Switzerland, Germany, Korea and Vietnam. Silk is actually only about 0.2% of the global textile market. The major producers of silk are in Asia – with 1 million workers employed to produce silk in China (inserco.org). The demand as well as the production of silk is quite global as you can see. The same applies for spider silk but while the demand is global, the supply is nonexistent.
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| Figure 2: The first textile made purely out of spider silk http://www.wired.com/images_blogs/wiredscience/2009/09/full-silk_hi-res_d66-06.jpg |
So, how can we get the amazing powers of spider silk without
having to harvest it from the wild? The answer to this questions is goats – and
not just any ordinary goats but spider-goats.
A spider-goat is
actually the name given to transgenic goats that have spider genes in them.
Scientists have added protein from the golden orb-weaver spider (Nephila) into the goats'
milk in order to make it easier to harvest spider silk. First, the scientists
found out which of the spider's genetic code in its genome is responsible for the
production of the single protein that makes up its dragline silk. Next, they
put that gene into the DNA of goat embryos next to the natural milk
production genes. Those embryos were then implanted into female goats.
The only way to find out whether or not a goat has the
spider gene is through genetic testing. Otherwise, they have exactly the same phenotypes.
Like normal goats, transgenic ones mature after around 18 months, which is also
when they start lactating. The spider silk proteins are in the goats' milk so
to get them out you just have to milk the goats. However, getting the silk out
of the milk is a bit harder. First, the fat is skimmed off and then the spider
silk proteins are processed out. Video 1 below from the National Science
Foundation explains the things above further.
Video 1: All about transgenic goats
https://www.youtube.com/watch?v=ktgACq4zcAU
From this video, you can see the example usage of spider
silk in the different industries as well as a basic overview on how transgenic goats
are produced on farms, explained by Randy Lewis, a molecular biologist at the
University of Wyoming and one of the leading figures for producing transgenic
goats to harvest spider silk. In addition to that, the milking process of
transgenic goats can be seen in Video 3.
Transgenic animals can be produced by scientists today
because of several breakthroughs in recombinant DNA or artificially-produced
DNA, genetic cloning, analysis of gene expression and genomic
mapping. The production of transgenic animals is basically the introduction of
a foreign gene from another species into an animal. In the case of the
spider-goats, it is the introduction of the spider dragline silk gene into a
goat. So far, there are three methods of producing transgenic animals, which
are DNA microinjection, retrovirus-mediated gene transfer and embryonic stem
cell-mediated transfer. The method used to make the transgenic spider-goats is
DNA microinjection.
The technique of DNA microinjection successfully produces
transgenic goats because introduced DNA from the spider integrates itself into
the germ line and is passed along to every single cell in the goat’s body. The
principles used for the first successful DNA microinjection in 1981 are still
used today with no major changes. The procedure for DNA
microinjection consists of five basic protocols, which are
the preparation of spider transgene DNA for microinjection, embryo
collection from donor goats, DNA microinjection into the goat embryos, embryo
transfer into female goats and identification of transgenic
goats. Figure 3 below is an illustration of the DNA microinjection itself, the
third basic protocol.
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| Figure 3: An illustration of DNA microinjection. The 'host cell' in the middle is the goat embryo and the 'microinjection needle with foreign DNA' contains the spider transgene http://images.tutorvista.com/content/biotechnology/micro-injection-process.jpeg |
In the preparation of the spider transgene DNA for microinjection,
the part of the genes of the spider that codes for the production of its
dragline silk is removed from one of its cells and then prepared for
microinjection. In the embryo collection from the donor goats, there are two
options - either to let the female egg fertilize naturally or use in vitro
fertilization (IVF). For the natural process, the scientists have to find
a healthy female goat and a healthy male goat. The male goat would then be
allowed to fertilize the egg of the female goat naturally. Then
the scientists extract what now is an embryo. For the IVF process,
one healthy egg is chosen from the female goat and sperms from the male
goat are placed in a petri dish. The fertilization will occur here thus forming
an embryo. In the DNA microinjection, the transgene from the spider is
injected into the extracted goat embryo using a needle. The process under a
microscope can be seen in video 2 below.
Video 2: DNA microinjection under a microscope
https://www.youtube.com/watch?v=h-Bfc1GPWpE
In the embryo transfer to female goats, the embryo
containing the spider transgene is placed back inside a womb of a female goat
and is then allowed to develop normally. The female goat will eventually give
birth to offspring with a normal phenotype. Therefore, to find out whether or
not the DNA microinjection was successful, scientists will have to do the
genetic testing. In the identification of the transgenic goats, scientists can
extract any cell from the offspring and then completely analyze the DNA to
see if the spider transgene is actually there. If it is there, it means that
the DNA microinjection process was successful and that they have created a
spider-goat.
Using transgenic goats to produce spider silk has several
benefits. The first one is that just by using the transgenic goats, stronger
and more elastic materials than ever before can be produced. These
materials include those in the industries of medicine, military, sports and
automotive. The most outstanding example of this would be the potential use of
spider silk in the military. According to Al Jazeera, “a layered piece of
rubbery silicone with 10 layers of spider silk painted on was enough to stop a
bullet. Without those incredibly thin layers of spider silk, the bullet went
right through.” (Phil Torres, america.aljazeera.com).
The second benefit is that goats are farm friendly animals.
They can be kept in large numbers together because they are not
cannibalistic like the spiders. In addition to that, they are also easy
to breed and handle and have been the farm animal of choice for a long time.
The last and most important benefit of using transgenic
goats is that they, pound-for-pound, produce as much milk as cows. While a
cow weighs about half of a car, a goat does not weigh anymore than an average
person. These beneficial reasons are why the scientists chose the goats to
become the transgenic species in or host organism the first place.
However, using transgenic goats to produce spider silk also
has its limitations. One of the limitations to using transgenic goats to
produce spider silk is the difficulty in finding the right gene codes in genome of the
spider and also the right host organism. A spider produces a variety of silk
types, not just the dragline silk that most people are interested in.
Therefore, it is hard to find the gene codes in the spider's genome that codes for the
dragline silk since it is the rarest silk that the spider produces. In addition
to that, it is also hard to find a host goat that would not reject the spider
transgene. This depends on the goat breed and whether or not there were any
other previous mutations in the breed, natural or manmade.
The next limitation is problems that can arise in the
offspring. One of these problems is that the goat born with the spider transgene
might not be the right sex for milk production. This is crucial because
scientists rely on the milk production as a natural outlet for the silk
production. If the goat were male, it would be harder to milk and harvest the
silk from than if it were female.
The last and most unfavorable limitation of all is the
overall small success rate of producing transgenic goats. From the results of a
transgenic goat program conducted in Israel from July 1995 to February 1996,
the small success rate of producing transgenic goats were proven because of the
86 kids born, only 4 were transgenic. (E. Gootwine, ncbi.nlm.nih.gov). This
gives us about a 5% chance of an offspring goat having the spider transgene in
them. These limitations are the reasons as to why there are not more companies
using transgenic goats to produce spider silk, despite the fact that it is a
very good business opportunity. This is worsened by the example of the company
Nexia Biotechnologies that infamously went bankrupt after successfully using
transgenic goats to produce spider silk.
Apart from these benefits and limitations of using
transgenic goats to produce spider silk, there are also ethical concerns that
could affect the successfulness of using the transgenic goats. Most of these
ethical concerns have to do with animal welfare. These are sparked mainly because
of the invasive nature of the procedures. In the procedures for the production
of the transgenic goat, scientists literally inject DNA from the spider into
the goats’ embryos. The main question raised because of this is “Are animals
that combine that combine species an unethical alteration of the natural order
of the universe?” Scientists and people who breed these transgenic goats obviously
say no to this. For example, Randy Lewis, a molecular biologist at the
University of Wyoming and a transgenic goat breeder says, “I would not say it’s
bizarre. I think that its certainly different but they’re absolutely normal. I
don’t think there’s anything different about them.” This quote was taken from
Video 3, which is below. From this quote, we can infer that people like Randy
see nothing ethically wrong with genetically engineering transgenic goats. We
now know what the scientists are saying, but what are others saying? In Figure
4, I took a screenshot of the comment section of one of the articles that I
sourced. This is the opinion of the public.
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| Figure 4: Comments of readers on an article about transgenic goats http://www.takepart.com/article/2014/04/10/gmo-goats |
As you can see, most people disagree with the idea of using
transgenic goats to produce spider silk saying that it is horrible and totally
inappropriate. The public has the most influence on the successfulness of this solution
from the ethical perspective because they are the majority. I myself do not
agree with the scientists or the transgenic goat breeders and agree with the majority
because I think that they are right, that genetically engineering these
transgenic goats is ethically wrong. I say this because I think that we humans
do not have the right to combine species like the transgenic goats do. Each of
the species on this Earth was created for a reason. We might not know what
those reasons are but this does not mean that we can exploit them to our
benefit. Even though transgenic goats are the most feasible solution to mass
produce spider silk, it is not ethically appropriate. These concerns from an
ethical perspective are equivalent to our unit question for the term: Should we
play God? In Video 3 below, the same is asked when reporter Adam Rutherford
visited Randy Lewis’ transgenic goat farm – should these animals really exist?
Video 3: Should transgenic goats really exist?
https://www.youtube.com/watch?v=B0zT9CN3-50
From this video, you can see the attitudes of Randy Lewis, a
molecular biologist at the University of Wyoming and one of the leading
transgenic goat breeders, as well as Adam Rutherford, a reporter. Adam was in a
state of disbelief throughout the video, constantly asking questions in a tone
that suggests so. On the other hand, Randy gives off a convincing attitude
while answering the questions asked by Adam, which suggests that he does not
think that there is anything weird with the transgenic goats – he thinks that it
is a miracle that they exist.
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