transgenic animals new
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Transgenic Animals
S.KARTHIKUMAR,M.Sc.,M.Phil.,M.Tech.,(PhD)ASSISTANT PROFESSOR
DEPARTMENT OF BIOTECHNOLOGYKAMARAJ COLLEGE OF ENGINEERING AND TECHNOLOGY
VIRUDHUNAGAR-626001TAMILNADU, INDIA
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Definition of Transgenic
Transgenic -> stable introduction of a gene into another organism
-> For Unicellular organisms (such as bacteria or yeast) all transformed cells are -> transgenic
-> For multicellular organisms (such as animals, plants,..) difference between: - manipulation of single cells -> cell line (expression in insect cells or mammalian cells) - manipulation of a whole plant or animal -> transgenic (can have a transgenic offspring!!!)
-> more difficult and expensive to create whole modified organism (transgenic) than just cell line!!!
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Transgenic versus Cloning
Transgenic -> creation of transgenic animal or plant (introduction of foreign gene into organism)
-> transgenic organisms produced by introduction of foreign gene into germ line (-> transgenic offspring!!!) -> introduction of gene into somatic cells -> gene therapy
Cloning -> obtaining an organism that is genetically identical to the original organism
-> such as Dolly the sheep -> asexual propagation of plants (taking cuttings)
Disease Models
• Animals genetically manipulated to exhibit disease symptoms so that effective treatment can be studied.
• Alzheimer’s Disease
• Cancer Treatments
Medical Applications
• Xenotransplantation• Nutritional Supplements• Pharmaceuticals
• Human Gene Therapy
Industrial Applications
• Chemical Safety Testing• Production of Material
– Military Uniforms
– Tennis Racket Strings
But How is it Done?
• DNA Microinjection
• Retrovirus-Mediated Gene Transfer
• Embryonic Stem Cell-Mediated Gene Transfer
• Sperm-Mediated Gene Transfer
• Somatic-Cell Nuclear Transfer
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The first days of an embryo
Embryonic stem cells (ES)
Used for retroviral infection
Fertilized egg
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Microinjection into the germ line -> transgenic animal
Gene injected into the male pronuclei
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Retroviral vectors into the germ line (8-cell embryo infected)
-> transgenic animal
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Engineered Embryonic Stem Cells (ES)
into the germ line (blastocyst) -> transgenic animal
Inner cell mass (ICM) of blastocysts can form all cells of the embryo -> Pluripotent-> Embryonic stem cells
Engineered ES -> can form any kind of cell in an embryo
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Gene Therapy – Viral gene transfer into somatic cells
Gene transfer into somatic stem cells -> gene therapy
Gene transfer via Virus
Target tissues: Bone marrow, liver, brain,[email protected]
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Gene Therapy – Viral gene transfer into somatic cells
Gene transfer into somatic stem cells -> gene therapy
Used for treating -> genetic diseases, such as diabetes, cancer, color blindness…
Different delivery methods
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Gene Transfer - what happens on DNA level
Integration into chromosome -> Recombinantion
Recombinantion can be -> homologous – non-homologous
- non-homologous event -> more frequently
- homologous event -> less frequent but desired
Knock-out mutants -> disrupt functional gene by integration of another gene into target geneUsed for:
-> study human diseases by creating model organisms
-> make minus mutant
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Cre-LoxP system:
- Inactivation of a gene (knock-out) in a specific cell type
- Activation of a transgene in specific cell type
Used for:
- Study biological consequences of tissue- specific gene inactivation
-> establishing models for human diseases
-> selective removal of kinesin II gene (expressed in retinal receptor cells)
-> leads to accumulation of opsin and arrestin -> cell death
-> result mimics aspects of a disease (inherited retinis pigmentosa)
-> large deletions in chromosome -> deletion in chr. 22 -> DiGeorge syndrome
(cardiovascular dysfunction)[email protected]
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Cloning of Dolly – Cloning Animals by Nuclear Transfer Technology
Critical for success:
Cell cycle of the somatic cells (udder cells) on plates was critical – they were kept in specific growth stage (diploid stage)
Of the 434 fused oocytes created during the experiment -> only Dolly survived to adulthood
Dolly was real clone (genotype identical) and could reproduce
Dolly was euthanized 2003 -> suffering from progressive lung disease
Since 1997 -> cloning of sheep, cows, mice, cats, other animals done
-> many of the clones developed severe diseases as they matured.
Until 1997, arrival of Dolly – not possible to produce an adult animal from a nucleus from an adult animal´s differentiated cell
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Cloning of Mammals – Reproductive Cloning
- Genotype identical
- Phenotype is not necessarily identical -> variation due to random events and due to environment
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Why do clones have health problems?
Telomeres are found at the end of each chromosome.
Shrinking of the telomeric ends of our chromosomes are a sign of aging of the cell.
Each cycle of cell division the telomeres are slightly shortened until they are too short for further replication -> cell death
Dolly´s telomeres (at the age of 3) have been as short as ones of the age of 6 -> clones age “faster”.
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Why do clones have health problems?
Differentiated cells have certain methylation pattern.
Cloned animals have abnormal methylation pattern originating from nucleus from differentiated cells
Some can be “re-set” (epigenetic reprogramming) to their undifferentiated state, some cannot -> faulty gene activation in cloned animal
-> so few cloned embryos survive
-> surviving clones have severe health [email protected]
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Production of pharmaceutical proteins -> drugs
Problems: Highly inefficient
Only 20% of the eggs survive and only 5% of them produce product
Transgenic Cattle, Sheep, Goat, Pigs
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Transgenic Cattle, Sheep, Goat, Pigs
- Protein production: in milk, blood, urin
- Animals (pigs) with modification of sugars on surface of organs
-> donor for organ transplants
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Transgenic birds and fish
-> improvement of agricultural value
Transgenic chicken:- Resistant to viral, bacterial diseases
- better feeding efficiency (fast growth, better meat quality, more meat
- less fat meat, less cholesterol in eggs
- maybe use of eggs as bioreactors for protein production
Transgenic fish: -> to support aquaculture- Increase growth rate (growth hormone)
- resistance to diseases
- Generation of model systems to monitor health hazard
(screening chemicals if they cause mutations)