Genetic Modification of Animals
Like bacteria and plants, animals can be genetically modified by viral infection. However, the genetic modification occurs only in those cells that become infected, and in most cases these cells are eventually eliminated by the immune system. In some cases it is possible to use the gene-transferring ability of viruses for gene therapy, i.e. to correct diseases caused by a defective gene by supplying a normal copy of the gene. Permanent genetic modification of entire animals can be accomplished in mice. The process begins by first genetically modifying a mouse embryonic stem cell. This is normally done by physically introducing into the cell a plasmid that can integrate into the genome by a process known as transfection. During transfection the DNA integrates into the animal genome via non-homologous recombination. This altered cell is implanted into a blastocyst (an early embryo), which is then implanted into the uterus of a female mouse. A pup born from this blastocyst will be a chimera containing some cells derived from the unmodified cells of the blastocyst and some derived from the modified stem cell. By selecting mice whose germ cells (sperm- or egg-producing cells) developed from the modified cell and interbreeding them, pups that contain the genetic modification in all of their cells will be born. Baylor College of Medicine currently has one of the largest transgenic mice facilities in the country.
There has also been the genetically manipulated bull Herman with 55 offspring. A human gene was built into his genetic code while in an early embryonic stage in 1990. As a result, milk from his female descendants contained the human protein lactoferrine, which can be used as medicine, but it was present at such low levels that it was not profitable to extract them.
Insects can be genetically modified by injecting them with artificial transposons and a source of the enzyme transposase. The transposon, which can include new genes, is then integrated into the genome. Such insertions are unstable and can «jump-out» in the presence of transposase.
Transgenic fish are often created by microinjection. First generation is mosaic but several lines have been produced with the transgene incorporated into the germ line and transgenic fish can then be produced «naturally» by crossing male and female gametes. Although many types of transgenic fish exist (e.g. for increased cold tolerance, antibiotic production, ornamental Glofish etc), the main focus had been on so-called growth hormone transgenic fish, mainly salmonids, tilapias and carps. These fish have an over-production of growth hormone which results in increased growth rate from a few percent up to 30-40 times that of wild-types. In some species, final size is increased as well as growth rate providing an incentive for commercial breeders to farm such fish. However, ecological concerns over potential negative effects of transgenic fish in nature largely prevent the commencement of commercial production. A large and important portion of the research on transgenic fish today is therefore focused on environmental risk-assessment of GH-transgenic fish. Problems encountered and advances within this field are summarized in Devlin et al (2006).
Exercises
A.Comprehension
I. Answer these questions.
1. What is a genetically modified organism? Give some examples.
2. What does genetic modification involve?
3. How can you characterize the process of transformation?
4. Where does genetic modification of animals occur? How?
5. What is used to introduce new DNA Into the receiving host?
6. Why are «knocked out» organisms used?
II.Illustrate the process of genetic modification of animals in one example.
III.Characterize each of the processes by which the genetic composition of bacteria can be altered.
IV.Agree or disagree with the following statements.
1. A genetically modified organism (GMO) is in organism whose genetic material has been altered using recombinant DNA technology.
2. The term «genetically modified organism» does not include transgenic substitution of genes from another species, and research is actively being conducted in this field.
3. Modification of plasmids is possible because of the double-helix structure of DNA
4. Genetic modification is achieved by expressing DNA molecules with restriction enzymes in extraneous fragments using DNA ligase.
5. Transformation refers to the introduction of new DNA into a bacterial cell by a bacteriophage, a virus that infects bacteria.
6. Transduction is a process by which some bacteria are naturally capable of taking up DNA to acquire new genetic traits.
7. In conjugation, DNA is transferred from one bacterium to another via a temporary connecting tube of protein called a pilus.
8. Knocked out organisms have a specific gene that has been functionally destroyed.
V. Summarize the text, using vocabulary from Exercise 6.
B.Vocabulary
VI. Give Russian equivalents of the following expressions:
| test tube | substitution | makeup |
| jellyfish | Basepair | conjugation |
| extraneous | Pup | electric |
| current transduction | to increase | incentive |
| salmonids | Uterus | growth rate |
VII. Find synonyms of these expressions among the words and word combinations of the words/expressions:
1) structure; composition; framework;
2) irrelevant; inappropriate; off the point;
3) to enlarge; raise; enhance; multiply;
4) motivation; encouragement; reason; inducement;
5) flow; stream;
6) a long cylinder, closed at one end, used in chemical experiments;
7) replacement; changeover; switch.
VIII. Translate the given words and expressions into English:
1)пробирка; 2)строение, структура; 3)замена, замещение; 4)медуза;
5)инородный; 6)пара оснований (ДНК); 7)электрический ток; 8)соединение, слияние; 9)преобразование, трансдукция; 10)матка, детеныш; 11)лососёвые; 12)темп роста, побуждение, стимул; 13)спираль.
Find the sentences in the text, where these words and expressions are used. Translate them into Russian.
C.Reading, Writing and Discussion
IX. Read the text carefully, without a dictionary. While reading, pay special attention to the words that you don’t know: look carefully at the context and see if you can get the idea of what they mean. After reading speak on: 1) regulation of gene expression; 2) the paces of making a glow-in-the-dark houseplant.
Regulation of gene expression is as important as gene function. Contained within our DNA sequence are elements known as promoters and repressors that allow individual cells to control which genes are expressed. This is how the individual cells in our bodies know which genes to use. There are genes specific to each tissue (muscle, brain, liver, etc.) in our bodies as well as «housekeeping genes» which are present in all cells. 1 Expressing genes in the appropriate tissue at the appropriate time is very important. Cancer, defined as any uncontrolled growth, is ultimately a result of misregulation of gene expression.
Genes maybe expressed in specific locations (e.g., tissue-specific genes), at specific times (e.g., embryo-specific genes), or in response to environmental stimuli (e.g., light-responsive genes). Viruses are powerful genetic engineering tools because of their ability to target specific tissues and express specific genes in those tissues. One of the reason that herpes virus is potentially useful for treating brain diseases because it infects brain cells and expresses specific genes in brain cells. The challenge is to disable the herpes-causing genes while introducing functional beneficial genes.
Applying what you've just learned, lets go through the paces of making a glow-in-the-dark houseplant.
The first thing we are going in need is a gene that makes things glow. One commonly used gene is the gene for the green fluorescent protein from jellyfish. This protein wouldn’t be of use for us though, because it only glows under ultraviolet light. The luciferase gene from fireflies generates its own light, but it requires energy to do so. We will use the luciferase gene for our experiment.
The next step is to consider regulation. I he luciferase gene requires energy so we don’t want it expressed everywhere, because it might result in stunted plants. For our project, we will use a light sensitive repressor and a leaf-specific promoter so that the leaves will light up only when the plant is in the dark. This will conserve how much energy the plant needs to use to glow.
One nice thing about working with plants is that you can grow a complete plant from any cell, bypassing the complications of dealing with germline cells. If we introduce our luciferase gene under the control of a light-sensitive repressor and leaf-specific promoter into mat lire plants, there are methods to isolate the «transformed» cells and regenerate them into complete plants.
This outline simplifies many of the required procedures. Finding light- sensitive repressors and leaf specific promoters is a feat in itself. The process of introducing DNA into plants and recovering the «transformed» plants is also cumbersome. Additionally, plants don't like to make proteins that they don’t need to, and may find ways to stop production of luciferase. The same general problems apply to humans and other animals as well. Thus, genetic engineers must develop efficient DNA delivery techniques and find appropriate promoters and modify genes/promoters so t hat they won’t be rejected.
X. Translate the text without a dictionary.
The History of GMO
The first GMO was created in 1973 by Stanley N. Cohen and Herbert Boyer, demonstrating t lie creation of a functional organism that combined and replicated genetic informal ion from different species.. In mid-1974, very soon after the first GMO was created, scientists called for and observed a voluntary moratorium on certain recombinant DNA experiments. One goal of the moratorium was to provide time for a conference that would evaluate the state of the new technology and the li.sks. if any, associated with it. That conference concluded that recombinant DNA research should proceed but under strict guidelines. Such guidelines were subsequently promulgated by the National Institutes of Health in the United States and by comparable bodies in other countries. These guidelines form the basis upon which GMOs are regulated to this day.
The first transgenic animals were mice created by Rudolf Jaenisch in 1974. Jaenish successfully managed to insert foreign DNA into the early-stage mouse embryos; the resulting mice carried the modified gene in all their tissues. Subsequent experiments, injecting leukemia genes to early mouse embryos using a retrovirus vector, proved the genes integrated not only to the mice themselves, but also to their progeny.
XI. Read the text. Express your own attitude to the problem raised in the text, giving your own arguments. Write a summary of the text.
Controversy
Genetic modification (GM) is the subject of controversy in its own right. Some see the science itself as intolerable meddling with «natural» order, despite many known examples of natural genetic crossings occurring throughout history (see for example horizontal gene transfer). While some would like to see it banned, others push simply for required labeling of genetically modified food. Other controversies include the definition of patent and property pertaining to products of genetic engineering and the possibility of unforeseen global side effects as a result of modified organisms proliferating. The basic ethical issues involved in genetic research are discussed in the article on genetic engineering.
In 2004, Mendocino County, California became the first county in the United States to ban the product ion of GMOs. The measure passed with a 57% majority. In 2005, a standing committee of the government of Prince Edward Island in Canada began work to assess a proposal to ban the production of GMOs in the province. This is a largely symbolic and empty gesture as PEI has already banned GM potatoes, which account for most of its crop. In California, Trinity and Marin counties have also imposed bans on GM crops, while ordinances to do so were unsuccessful in Butte, San Luis Obispo, Humboldt, and Sonoma counties. Supervisors in the agriculturally-rich counties of Fresno, Kern, Kings, Solano, Sutter, and Tulare have passed resolutions supporting the practice.
Currently, there is little international consensus regarding the acceptability and effective role of modified «complete» organisms such as plants or animals. A great deal of the modem research that is illuminating complex biochemical processes and disease mechanisms makes vast use of genetic engineering.
An often cited controversy is a hypothetical Technology Protection technology (dubbed terminator by non-governmental organization). This yet-to-be-commercialised technology would allow the production of first generation crops that would not generate seeds in the second generation because the plants yield sterile seeds. The patent for this so-called «terminator» gene technology is owned by Della and Pine Land and the United States Department of Agriculture. Delta and Pine I and was bought by Monsanto in August 2006. In addition to the commercial protection of proprietary technology in selfpollinating crops such as soybean (a generally contentious issue) another purpose of the terminator gene is to prevent the escape of genetically modified traits from crosspollinating crops into wild-type species by sterilizing any resultant hybrids. The terminator gene technology created a backlash amongst those who felt the technology would prevent re-use of seed by farmers growing such terminator varieties in the developing world and was ostensibly a means to exercise patent claims. Use of the terminator technology would also prevent «volunteers», or crops that grow from unharvested seed, a major concern that arose during the Starlink debacle.
While scientific progress on molecular biology has a great potential to increase our understanding of nature and provide new medical tools, it should not be used as justification to turn the environment into a giant genetic experiment by commercial interests. The biodiversity and environmental integrity of the world’s food supply is too important to our survival to be put at risk.
What are GE plants?
These are plants, in which foreign genes were inserted to develop the traits of herbicide tolerance, pest resistance, and increased crop capacity.