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The Goats with Spider Genes and Silk in their Milk - Horizon Playing God - BBC Two02:53

The Goats with Spider Genes and Silk in their Milk - Horizon Playing God - BBC Two

Transgenic goats

This is a simple diagram of how the gene from a spider is placed into a goat. Link: http://heiferinyourtank.typepad.com/theres_a_heifer_in_your_t/2011/08/how-did-they-get-the-silk-in-the-milk.html

Spiders silk is a protein-based "biopolymer" that is secreted by the epithelial cells of a spider[2.] The silk can have a variety of  medical and safety applications useful to humans due to its incredible strength, elasticity, stretchability, and waterproofing. Some medical applications include artificial ligaments and tendons, eye structures, and jaw repair. Some safety applications include bullet proof vests and car airbags [3.] It would take thousands of spiders and a lot of time for just one bullet proof vest and since spiders are territorial they will kill each other when placed together. Since this is not practical for commercial use the genes that code for the silk protein were genetically engineered into goats so the silk protein could be excreted in their milk [3.] 

Structure of Spider silkEdit

The primary structure of spider silk is an amino acid sequence that is composed of repetitive glycine and alanine blocks. The secondary structure is a short side chain of alanine that is in the form of beta sheet of nanofibril. The glycine is in a amorphous matrix that consists of both alpha and beta sheets [5.] 

Genetic ModificationsEdit

Dragline silk genes of the spiders Araneus diadematus and Nephila clavipes produce a mixture of two proteins from the epithelial cells of the amputate glands of the spiders. These genes encode proteins that have both crystalline alanine-rich  (ASAAAA) strings and glycine-rich amorphous regions (GGYGPG) which provide mechanical function and elasticity respectively [4.] In one study the genes ADF-3/MaSpII and MaSpI were used to produce soluble recombinant dragline silk proteins [2.] The genes were placed into the germ line cells of goats and they were expressed in the bovine mammary epithelial alveolar cells (MAC-T). These were used because they are able to excrete high levels of the proteins [4. ]
Spider silk protein

This figure shows the structure of a beta-sheet protein, Z1-Z2 telethonin complex, in the giant muscle protein titin. The inset shows the orientation of the protein backbone of three beta strands (in purple) with hydrogen bonds (yellow) holding the assembly together. Buehler and Keten found that hydrogen bonds in beta-sheet structures break in clusters of three or four, even in the presence of many more bonds. (Credit: Sinan Keten and Markus Buehler)

Original goal of the GMO GoatEdit

In 2000 a company called Nexia Biotechnologies trademarked a fiber called BioSteel. The company was funded by the US Army to build body armor and other devices for the military. This was because the silk was strong, flexible, and lightweight [7]. The BioSteel was made from spider silk that was produced by transgenic goats. In 2009 the company went bankrupt and they sold their two transgenic goats [1.]GEORGE IS GAY'  

However, there has been a study by Altman GH et al., which showed that the silk fiber is able to be used in engineering ligaments like the ACL. Human progenitor bone marrow stromal cells were combined with the silk matrix and the expression of collagen I and III as well as tenascin-C markers were assessed for compatibility. They found that the silk matrix was not only compatible with human cells it also supported the attachment, expansion, and differentiation of the cells. Therefore the silk protein is not only able to act like a ligament it can also support the growth of those ligaments [9.]

ReferencesEdit

1. Wikipedia, BioSteel (2013) Link: http://en.wikipedia.org/wiki/BioSteel

2. Lazaris A. et al. Spider silk fibers spun from soluble recombinant silk produced in mammalian cells. Science. (2002); 295:472-6 Link: http://www.ncbi.nlm.nih.gov.ezproxy.uvm.edu/pubmed/?term=Spider+silk+fibers+spun+from+soluble+recombinant+silk+produced+in+mammalian+cells.

3. Zyga L. Scientists breed goats that produce spider silk. Phys.Org. (2012) Link: http://phys.org/news194539934.html

4. The San Diego Biotech Journal. [http:// http://frank.itlab.us/photo_essays/papers/spinneret.pdf Spider Silk Biotechnology ]( 2002) Link: http://frank.itlab.us/photo_essays/papers/spinneret.pdf

5. Wikipedia, Spider Silk (2013) Link: http://en.wikipedia.org/wiki/Spider_silk

6. Utah State University, Synthetic Silk (2010) Link: http://sbc.usu.edu/htm/silk

7. Argals A, et al. [http:// http://heiferinyourtank.typepad.com/theres_a_heifer_in_your_t/2011/08/how-did-they-get-the-silk-in-the-milk.html How did they get silk in the milk?] (2011) Link: http://heiferinyourtank.typepad.com/theres_a_heifer_in_your_t/2011/08/how-did-they-get-the-silk-in-the-milk.html

8. Toronto Sun. QMI Agency. (2010) Link: http://www.torontosun.com/news/world/2010/05/18/13996146.html

9. Altman GH. et al. Silk matrix for tissue engineered anterior cruciate ligaments. 2002; Oct: 23(20):4131-41. Available from: http://www.ncbi.nlm.nih.gov/pubmed/12182315

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