Genetics is common to all living things, from the simplest unicellular organism to the most advanced species-human (goats come pretty close too!). The basis for this common factor is that we all have DNA, and through its sequence in our genes, it determines our fate as to physical characteristics and development. The sequence of the DNA, a.k.a. the genetic code for each individual, is derived from the order of the four nucleotides; adenine (A), guanine (G), cytosine (C), and thymine (T). These four nucleotides make up the rungs of the DNA ladder, and each is attached to a sugar and a phosphate, which thus make up the backbone of the ladder. So, the double helix of the DNA, which makes up our chromosomes, is two strands of complementary DNA with a nucleotide paired to its complement, i.e. A-T, C-G, G-C, and T-A. Due to this complementary structure, the sequence, hence one's DNA code, is forever conserved. This structure of DNA was discovered in 1953 by Doctors Watson and Crick, which later earned them the Nobel Prize for their breakthrough. In the early 1960s, it was Dr. Nirenberg who broke the genetic code, the key to how the sequence of the nucleic acids A, T, C, and G determined how life is constructed. This code is constructed by nature in triplets, termed "codons," and each codon determines a specific amino acid, the building blocks of proteins. Proteins provide the structure, framework, and machinery; and direct or mediate the metabolic processes within every cell of every living thing on this planet.
The DNA triplet codon can be any combination of three of the letters A, T, C, and G. An example would be GCA which codes for the amino acid alanine. This would mean that at this codon's respective position in the gene sequence, alanine would be inserted into that same position in the amino acid sequence of the protein itself. It sounds so simple for such a complicated system as life itself, but please understand that nature itself is truly the most simple, efficient system available in the universe. Truly, the progression from the genetic code to proteins is no more complicated than those colored plastic blocks that our infants put together in a long chain and make us so proud! Using this analogy is great because this is exactly how the coding sequence in our genes works. A gene contains the "code" for roughly anywhere from 100 to 1,000 amino acids. These "building blocks" are then assembled into a simple protein; or are assembled into a protein sub-unit, to make a more complex protein. The hemoglobin protein which carries the oxygen in the blood in the body is a protein consisting of four protein sub-units that link together to form the active, functional, protein in our blood. Proteins in living systems provide all that is necessary for life to exist, from enzymes that catalyze the biochemical reactions, protein hormones such as insulin, to the structure of our cells, organs, and muscles. It is the proteins in goat milk or lack thereof compared to cow milk that makes it great for chèvre or for infants who are allergic to cow milk. Proteins indeed make the living world exist.
The genetic code makes us what we are to a point, but man's hemoglobin is not that much different from the goat's hemoglobin. They both perform the same function and are relatively identical in the gene sequence. But what does make man so different than, say a goat, is how all the related and unrelated genes are packaged and regulated. Mammals have about 80,000 functional genes, however, the DNA that makes up these coding sequences is less than 20% of the total DNA contained in each and every one of our cells. This leaves greater than 80% of the DNA as non-coding DNA. We understand that some of the non-coding DNA regulates and manages the coding sequences, but a majority is termed junk DNA and we really have no idea as to it's purpose, if any. All cells that make up an individual plant or animal contain the exact same copies of all the DNA unique to that individual. The DNA in each cell is packaged into what are called chromosomes, long strands of the coding and non-coding double helix DNA held and condensed together by proteins. Higher life has two copies of each chromosome termed autosomes, and in mammals, sex is determined by two chromosomes called the sex chromosomes. Mammals that have two X sex chromosomes are females, and those possessing X and Y sex chromosomes are males. Similarities to this sex determination scheme are found in other animals. Man has two copies each of 22 autosomes, and two sex chromosomes, giving a total of 46 chromosomes in each cell (except the sperm and egg). Goats have two copies each of 29 autosomes, and two sex chromosomes giving a total of 60 chromosomes in each cell (except the sperm and egg).
Reproduction in mammals is accomplished by fertilization of the female's egg cell by the male's sperm cell. The egg cell is produced in the female's ovaries and the sperm is produced in the male's testis, through a process called gametogenesis (eggs and sperm are called gametes). Remember that each cell in an animal contains a pair of each distinct chromosome, and gametogenesis reduces this down to a single copy of each chromosome, including the sex chromosomes. Therefore, when a sperm and egg unite during fertilization, the resultant fertilized egg, called the zygote, again possesses a pair of each chromosome. This zygote will then begin dividing by a process called embryogenesis, resulting in the kid being born. It is the male's sperm cell that determines the sex of the resultant offspring, since each sperm will either carry an X or a Y sex chromosome, fertilizing the female's egg cell which will always have one X chromosome. The above describes sexual reproduction in nature, and by such the offspring inherit a copy of each respective gene from their mother and father. It is the interaction between these maternal and paternal genes through simple dominant and recessive characteristics that give rise to basic traits as hair and eye color, and even human familial diseases such as sickle cell anemia and cystic fibrosis. However, most traits are the result of more than one gene, called polygenic inheritance, and most traits are subject to environmental influences and regulation.
Above is a very quick lesson on how DNA determines life itself; and, by all means, there are many processes that have not been explained, and many that man does not yet fully understand. It is merely some background so that we may understand the second part of this article, the use of transgenic goats in medicine, science, and industry.
Part II
Transgenics is the introduction of foreign genetic material (DNA) into a recipient's genome. The recipient can be anything from bacteria or yeast cells, to plants or mammals. For example, human insulin is now being produced by E. coli bacteria on an industrial scale. Prior to this, insulin for diabetics was obtained from cow or pig pancreas, a very laborious and low yield process. Also, the cow or pig insulin differed slightly from human insulin so it was not 100% effective. Researchers were able to isolate the human gene for insulin, transfer the gene (hence transgenics) into the bacteria so that the bacterial cells produce the insulin in large amounts even though the bacteria have absolutely no use for the protein hormone. This was truly the first milestone in human medicine benefiting from genetic engineering. Since then, human, plant, and animal genes for a variety of proteins have been transferred into recipient organisms for basic research and other applications including medical treatments, agriculture, and industrial processes. However, not all ventures have proved successful, lending truth to the adage, "It's not nice to fool with Mother Nature."
Bacteria seem to be the most logical choice for a transgenic recipient organism: there are no ethical considerations, they are easily grown and harvested, and purification of the transgene product is simple. The drawback is that bacteria are very primitive life forms, and products that are derived from more advanced life need to undergo processing or modification that only advanced life is capable of performing. In the 1980s, transgenic mice, rabbits, and pigs were developed, expressing a variety of transgenes. For research applications these transgenic animals are excellent, and still extensively used, but for production of a product on a commercial scale, they are inefficient. When scientists put their minds to commercial production of a gene product, they deduced the best method would be production by the mammalian milk gland. Milk already has a large amount of native proteins present, it is easily collected and processed, and of course the machinery and methods for collection and processing of milk on a large scale are well established. The mammal to be used needs to be easily managed, milked, and have a relatively short generation time (conception to milk production). Mice, the model system for most everything in the laboratory, have a generation time of three months and an annual milk yield of one ml (Can you imagine trying to milk a mouse?). At the other end, cows have a generation time of three years and an annual milk yield of over 2,000 gallons. Goats have a generation time of 18 months, and as a dairy breed, show an efficiency of milk production that is unrivaled. Therefore, goats are the mammal of choice for a transgenic dairy production herd.
The basic method for inserting a foreign gene sequence into a recipient goat's genome is the gene for the target protein must be constructed in a way to be expressed solely in the goat's mammary gland. There are half a dozen proteins that occur only in milk, and these fall into two classes: caseins and whey proteins. The sequence of these genes have been determined for a variety of mammals, and contained within these sequences are the mammary gland specific regulator and promoter regions that "turn on" the production of the milk proteins in milk. The target protein gene is combined with the mammary regulator and promoter sequences; and then replicated many times over through recombinant DNA techniques in the laboratory. Then, thousands of copies of the target protein's gene are microinjected into the sperm pronucleus of a fertilized egg (zygote). The sperm pronucleus is the sperm's genetic material prior to fusing with the egg nucleus after fertilization. By inserting thousands of copies of the target sequence there is a good chance one copy will incorporate itself into the genome because of the engineered complementary sequence of the transgene. Subsequently, the developing embryo will then be inserted into a surrogate doe, who then will carry it to full term. After birth, the kid will then be genetically tested to determine if the transgene was incorporated into the goat's genome. If it has, and it is a female, it will produce the transgene protein in its milk. The scientists are even able to induce lactation at an early age without breeding, even in the buck kids, to start pilot studies, perfect methods of purification, or begin testing of the transgene protein in preparation for clinical trials if it is to be used for medicine. However, if the transgene protein is at the stage of full scale production, the doe or buck will be raised to normal maturity and become the founder stock of the transgene herd. By simple Mendelian inheritance patterns, mating the founder transgene doe or buck back to a normal doe or buck yields progeny of which 50% will carry the transgene. These transgenic kids are heterozygous for the transgene. Mating two heterozygous transgenic kids will yield 25% homozygous transgenic progeny, 50% heterozygous transgenic progeny, and 25% non-transgenic progeny. This is how the transgenic herd is produced.
The whole process of transgenics has been named Molecular Pharming in the field of biotechnology. There are currently two very large corporations undertaking goat pharming, Genzyme Transgenics Corporation based in Massachusetts, and Nexia Biotechnologies based in Quebec, Canada. Both are publicly traded on the stock exchange, and both are doing quite well. It seems that (it's hard to speculate what's going on in their boardrooms) Genzyme is focusing on developing goat pharmed medicines and tools for medical research, while Nexia is pursuing the more industrial applications of goat pharming. Genzyme's main product so far is Human Anti-Thrombin III (ATIII), an anti-clotting factor used in heart patients. Pre-clinical trials proved successful and were approved by the FDA and clinical trials are now underway. The market for ATIII is $200 million annually, and this amount of the transgenic protein can be produced by a herd of less than 100 goats, each initially costing a half to $1 million per doe. We can see that the potential profits in goat pharming are enormous! Genzyme has received a patent on the ATIII protein, and is producing it at their 7,200 sq. ft. dairy facility in Massachusetts. They currently have a herd of 2,000 goats on the 300 acre facility. The goats were from a high milk yield line imported from New Zealand. Nexia Biotechnologies' top pharm product is Biosteelä, genetically engineered spider silk proteins being produced in goats milk. Forged over 400 million years of evolution, the spider silk is considered the perfection of fibers. It is three times stronger than Kevlarâ, which is used to make bullet proof vests, and the strongest material on earth that can be woven into a fiber. It can withstand up to 600,000 lbs. per sq. in. pressure.
For years industry had been trying to domesticate spiders like silkworms, but they proved to be too territorial and vicious. Now, Nexia is breeding the transgenic herd using more than 1,000 goats on a farm outside Montreal and a decommissioned military base in Plattsburgh, NY. They, too, have a patent on Biosteelä, and their stock is soaring. Nexia has also received a research and development contract from the U.S. Army for another transgenic goat pharm product, Protexiaä, a form of butyrylcholinesterase (BchE). BchE may be used to prevent the toxic effects of nerve agents and other organophosphate compounds, is present in small quantities in our blood naturally, but is not available in the large quantities needed to protect our military personnel or public in the case of a nerve agent chemical attack. Using its transgenic goat technology, Nexia plans to produce bioactive Protexiaä protein in goat milk in large quantities, thereby providing the drug to protect large numbers of people. These are the main, industrial transgenic goat pharm products being developed currently, but you can bet the think tanks are hard at work. There are also numerous projects underway by universities and the like to make proteins for use in research, both basic and medical, such as fusion proteins to target cancer cells and monoclonal antibodies.
In summary, the last 50 years of DNA research and discoveries have paved the way for perhaps an unforeseen trend in the use of domestic goats, and really it is mainly based upon the goat species being nature's foremost and most efficient dairy animal. Goats have been milked for thousands of years, and are used extensively for the production of antibodies for use in biological research. But now, with the advent of the field of transgenic goat pharming, investors are staking hundreds of millions of dollars on the age old practice of goat dairy production. Indeed, think of it, a product of goat milk is helping save lives of cardiac patients, will save the lives of law enforcement officers and military personnel who wear bullet proof vests, and could possibly thwart global terrorism by protecting against chemical nerve agents. In biblical times, a family's wealth was measured by the size of their goat herd; in today's day and age it is the goat that is responsible for the wealth of some upper level stock portfolios.
