What is Transgenesis? Edit
Transgenesis is the process of introducing an exogenous gene – called a transgene – into a living organism so that the organism will exhibit a new property and transmit that property to its offspring. Transgenesis can be facilitated by liposomes, plasmid vectors, viral vectors, pronuclear injection, protplast fusion, and ballistic DNA injection. Transgenic organisms are able to express foreign genes because the genetic code is similar for all organisms. This means that a specific DNA sequence will code for the same protein in all organisms.
TRANSGENESIS WHEN USING PLASMIDS FROM BACTERIA: The plasma DNA is cut using restriciton enzymes, while the DNA to be copied is also cut with the same restriction enzyme, producing stick-ends. This allows the foreign DNA to hybridise with the plasmid DNA and be sealed by DNA ligase enzyme.
An example of an organism on which transgenesis is currently commonly performed on are mice.
Paratransgenesis: Constructing the enemy withinEdit
Paratransgenesis is a technique that attempts to eliminate a pathogen from vector populations through transgenesis of a symbiont of the vector. The goal of this technique is to control vector-borne diseases. The first step is to identify proteins that prevent the vector species from transmitting the pathogen. The genes coding for these proteins are then introduced into the symbiont, so that they can be expressed in the vector. The final step in the strategy is to introduce these transgenic symbionts into vector populations in the wild.
The first example of this technique used Rhodnious prolixus which is associated with the symbiont Rhodococcus rhodnii. Rhodnious prolixus is an important insect vector of Chagas's disease that is caused by Trypanosoma cruzi. The strategy was to engineer R. rhodnii to express proteins such as Cecropin A that are toxic to Trypanosoma cruzi or that block the transmission of Trypanosoma cruzi.
In order to perform paratransgenesis, there are several requirements:
- The Symbiotic bacteria can be grown in vitro easily.
- They can be genetically modified such as through transformation with a plasmid containing the desired gene.
- The engineered symbiont is stable and safe.
- The association between vector and symbiont cannot be attenuated.
- Field delivery is easily handled.
In the diagram shown in the above right, the technique of paratransgenesis is being performed:
1. There is in vitro cultivation of a microorganism (symbiont), which means it is being grown outside of its original organism home.
2. The symbiont is being recombinated so that it is ready to be altered in genetic composition.
3. The trypanosoidal factor is secreted into the symbiont to counter the disease in the original organism.
4. The symbiont is inserted back into the targerted original organism.
5. The symbiont will not interupt the life cycle of the trypanosome, which is causing the disease.
In this section there is a link to a Paratransgenesis Jeopardy game so that you can test your knowledge of this technique by yourself or with your classmates/friends. Have Fun!
Answers to Paratransgenesis Jeopardy:
Terms You May Not KnowEdit
Exogenous Gene- A gene from another organism
Liposomes- artificially prepared vesicles made of lipid bilayer
Plasmid Vectors- Plasmids used in genetic engineering are called Plasmid vectors
Viral Vectors- A tool commonly used by molecular biologists to deliver genetic materials into cells. This process can be performed inside a living organism (in vivo) or in cell culture(in vitro). Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect.
Pronuclear Injection- The use of a fine needle to inject DNA into the nucleus of an unfertilized egg.
Protoplast Fusion- It is also known as Somatic Fusion and is a type of genetic modification in plants by which two distinct species of plants are fused together to form a new hybrid plant with the characteristics of both, a somatic hybrid.Ballistic DNA Injection- Ballistic DNA Injection also known as either particle bomobardment, microprojectile gene transfer, or the gene-gun, was first developed for gene transfer into plants. Since its initial introduction, it has been modified to transfer genes into mammalian cells both in vitro and in vivo.
Symbiont- An organism in a symbiotic relationship. In cases in which a distinction is made between two interacting organisms, the symbiont is the smaller of the two and is always a beneficiary in the relationship, while the larger organism is the host and may or may not derive a benefit.