Transgenic Animals Flashcards
What are the genetic hybrids?
Mule
Liger
Tiglon/tigon
Zonkey
Zedonk
What is a zedonk?
A male donkey and female zebra
What is a zonkey?
A male Zebra and female donkey
What is a tiglon/tigon?
A hybrid cross between a male tiger (Panthers Tigris) and a lioness (Panthera Leo)
What is a Liger?
A hybrid cross between a male lion (Panthera Leo) and a females tiger (Panthera Tigris)
What is a mule?
A cross between a male donkey and a female horse
What are transgenic animals?
A transgenic animal is one that carries a foreign gene that has been deliberately inserted into its genome
The foreign gene is constructed using recombinant DNA methodology
The use of such animals in research, medical fields, and industry has many possibilities
-However, there remain many ethical and legal questions regarding their creation and usage
Give a Brief historical background of transgenic animals
In 1977 Gurdon and others showed that Xenopus oocytes provided an important expression system for molecular biology
- The genes they injected into Xenopus oocytes were transcribed and translated
- The term transgenic animals was coined by Gurdon and Ruddle in 1981
What are the general benefits of transgenic animals?
- agriculture
- medicine
- industry
What are the transgenic animal benefits to agriculture ?
To improve the productivity of livestock (muscle mass & wool quality)
- To improve disease resistance in animals
- Offers farmers an easy way to increase yields
What are the benefits of transgenic animals to the medical industry
A. Xenopus transplantation -transplant organs may soon come from transgenic animals
B. Nutritional supplements and Biopharmaceuticals
- Products such as insulin, growth hormone, and blood anti-clotting factors have already been obtained from the milk of transgenic cows, sheep or goats
- The first transgenic cow (Rosie) produced human protein-enriched milk at 2.4 grams per liter
C. Human gene therapy
-human gene therapy involves adding a normal copy of a gene (trans gene) to the genome of a person carrying defective copies of the gene
D. Medical information
-provide fundamental inform on living organisms and human diseases
What are the industrial applications in transgenic animals
Toxicity-sensitivity transgenic animals have been produced for chemical safety testing
Animals have been used as “Bioreactors” to produce proteins. Genes for desired are introduced via transgenics to the target cells
Bio steel is an extraordinary new product that may soon be used in bullet proof vests and in suture silk for stitching wounds
What are the transgenic models in drug development ?
- Search for Jew drug targets
- Models for Target Validation: Desire Models, Reporter mice used to monitor gene expression, Mice with human drug targets (e.g., knock-in mice)
- Safety testing
- Protein production
- Drug screening
- used for screening of many pharmaceutical drugs
What are the problems associated with transgenic animals?
- Inserted gene has multiple functions
- Breeding problems
- Sometimes leads to mutagenesis and functional disorders
- Low survival rate of transgenic animals
What are the environmental and ecological concerns of transgenic animals
- Competition with wild populations
- Gene introversion effects on wild gene pool
- Ecological disruption due to changes in prey size and other niche requirements
- Engineering approaches are unproven
- Bio-containment issues still not resolved
What are the methods of producing Transgenic animals?
- embryonic stem cell method
- the pro nucleus method
- retrovirus mediated gene transfer
Describe the Embryonic Stem Method
-Embryonic stem (ES) cells are collected from inner mass of blastocysts (about a wk old embryo)
They are then mixed with DNA containing gene of interest
- Some of the ES cells will absorb the DNA and become transformed
- Transformed ES cells are injected into inner cell mass of a host blastocyst
- Blastocyst is then injected into a foster mother
- Foster mother will give birth to baby mice
Describe the pro nucleus method of forming transgenic animal
- Based on the introduction of linear DNA sequences into the chromosomes of fertilized eggs
- First, DNA with the trans gene of interest is formed.
- then there is micro injection of desired DNA into the male pro nucleus
- Leading to formation of diploid zygote
- Mitotic division & formation of two-cell embryo
- Transferring to foster mother (Pseudopregnant mother)
- Formation of new individual (Baby mice are born)
What are the two methods of transgenic animals?
- Select for stem cells expressing desired genes
- inject transformed ES cells into inner cell mass
- inner mass of cells from blastocyst is implanted in the uterus - Desired gene with vector is extracted from pronuclei of fertilized egg
- implant in uterus
After both methods, offspring should be tested for presence of gene. Male heterozygous offspring to produce homozygous transgenic strain
What are retrovirus mediated gene transfer?
Retroviruses are used as v3ctors
To transfer genetic material into the host cell, resulting in a chimera
-an organism consisting of tissues or parts of diverse genetic constitution
What are the examples of transgenic animal?
Transgenic fish: Tilapia, Salmon/trout, catfish can grow up 6 times faster than wild type fish. Most have extra copies of growth hormone (GH) gene
Glowfish is a transgenic stamina of zebra fish containing red fluorescent protein gene from sea anemones
Transgenic Mice: Knick out mice
Transgenic goats(Silk-milk goats): they produce spider silk in their milk
What are the methods of producing transgenic fish?
DNA is delivered to fertilized fish eggs via:
- Micro injection
- DNA injected by fine glass needle
- Sperm mediated gene transfer
- sperm coated with recombinant DNA
- Electroporation
- eggs are subject to fluctuating electric fields
- Viral mediated gene transfer
- Virus particle delivers recombinant DNA
What are the current limitations of transgenic animals?
- low germline transmission
- variable number of copies inserted
- Insertion site different for each individual (pre-founder)
- uncontrolled transgene expression
- Difficulty in monitoring trans gene expression
- Insertion site affects other genes
Describe Gene targeting technologies
Adding genes is only one side of the transgenic story. Genes can also be taken out
- Gene targeting involves gene knockout and targeted gene replacement
- Targeted knockout involves the deletion or disruption of a specific gene
- Gene targeting is a powerful technique used by geneticists to understand the function of genes
What are knockout organisms/ knockouts?
Knockouts are used in learning about a gene which it has an unknown or incompletely known function
- Researchers draw inferences from the difference between the knockout organism and normal individuals
- This has been achieved in yeast, Drosophilia and mice
What is the knockout mice?
A true-breeding mouse strain lacking the function of a gene.
Because the gene has been replaced by either a null allele or a specific mutagenized allele
What are the uses of a knockout mouse?
- As models for some human genetic disorders e.g. CF & Duchenne muscular dystrophy
- To study genetic control of early development and behavior
What are the two things required for knockout mice?
- A culture of mouse embryonic stem (ES) cell
- A disrupted version of the gene of interest called target construct
The target construct contains the Neo and thymidine kinase (TK) selectable markers and 6-10 kB of genomic DNA from the targeted gene(to ensure an adequate targeting efficiency)
-The neo^r gene confer resistance to the antibiotic neomycin while the viral tk gene encides the enzyme, thymidine kinase
What is a compete knockout?
This is an offshoot of gene knockout technology where a specific target gene is eliminated from a single organ in the body of an experimental animal, rather than the whole body, as with conventional gene knockout technology
- It can be applied to eukaryotic and Prokaryotic systems and allows for more sophisticated experiments
- The most commonly used technique in doing this is the Cre-Lox recombination system
What is the Cre-Lox recombination?
Cre-Recombinase is a tyrosine recombinant enzyme derived from the P1 Bacteriophage
- It is known to catalase the site specific recombination event between two DNA recognition sites(loxP sites)
- DNA sequences found between two loxP sites are said to be “floxed”
- Cre recombinase is a widely used tool in the field of molecular biology
- The enzyme’s unique and specific recombination system is exploited to manipulate genes and chromosomes
What is the neo^r?
This sequence provides resistance to the drug neomycin and provides a selectable marker for ES cells which have incorporated the targeting construct into their genomes (either randomly or by homologous recombination)
What is the tk of the Gene targeting construct?
Encodes for the enzyme thymidine kinase that acts on the gancyclovir to produce a toxin. This provides a negative selectable marker for cells that have randomly incorporated the targeting construct into their genomes
What is the *** of a gene targeting construct?
This region may contain nothing in the case of a “knockout” or may contain a modified form of the host gene (e.g. mutated form) that is being targeted
What is the (purple block) of a gene targeting construct?
Sequences which are identical to sequences flanking the gene that is being targeted. These are the sites where homologous recombination into the host genome will occur (crossing over) during transfection
How does a successful gene targeting works?
Host genome showing gene to be targeted for deletion
Host genome showing the results of a successful gene targeting
These ES cells will be resistant to neomycin and will survive in the presence of ganyvclovir
Transfection of ES cells with a targeting construct can produce three different results….
….with respect to integration into the genome, each with possibilities for selection:
A) NO INTEGRATION (most probable )- negatively selected by neomycin
B) RANNDOM INTEGRATION(next probable)- negatively selected by gancyclovir
C) INTEGRATION BY HOMOLOGOUS RECOMBINATION(least probable)- positively selected by both neomycin and gancyclovir
Explain the significance of loxP
The loxP site can be inserted on either side of a piece of DNA
(A) If Cre recombinase is then expressed in the cell, the loxP site will be cut and joined together, removing the piece of DNA between the two sites
(B)Since the loxP site is directional, it can also used to invert pieces of DNA which are between it.
Here two loxP sites which are inserted on either side of a piece of DNA in opposite directions. Once Cre is expressed, the loxP sites are both cut and the piece of DNA inverted and reattached
