Chromosome manipulations


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Chromosome manipulations

  1. 1. Chromosome Manipulations ANIMAL BIOTECHNOLOGY
  2. 2. Benefits of Genetically Engineered Animals  Used to develop new medical treatments  Improve our food supply  Enhance our understanding of biology of all animals, including humans
  3. 3. Animal Models  Animal systems are a model for the human system  Polio vaccine was developed using animals as test systems  Cataract surgical procedures were developed with animals  Dialysis was tested first in animals before being applied to human conditions
  4. 4. Regulation of animal research  Animal Welfare Act  Sets specific regulations regarding, housing, feeding, cleanliness and medical care of animals  Researchers must first develop a plan describing Appropriateness of species to be used  Minimum number of animals needed for test    Oversight committee reviews and approves plan Government agencies monitor welfare of the test animals
  5. 5. Phase Testing  Testing a new product for safety in humans involves vigorously following scientific methodology developed for animal systems  Involves collecting data from a statistically significant number of trials (experiments) in lab cell tissue cultures, in live animals and in human subjects.  3-stages of testing Human trials Animal model Tissue culture if successful if successful
  6. 6. Testing  If test results using cell cultures indicates toxicity of product, then product will never be tested on live animals.  Testing on live animals requires evaluation of more than one species, since different species may respond differently.
  7. 7. Phase Testing  Animal models can provide the following information on a new product Absorption of chemical by body  Body metabolism of chemical  Time require for chemical or product to be excreted   If significant problems are encountered with product in live animals, then product is never tested in humans.
  8. 8. Side-effects of new drugs discovered in animal models  Example  Propecia Used to encourage hair growth Animal studies indicated that serious birth defects occurred in male offspring when pregnant animals were given large doses of drug As a result of animal tests, warnings were put on containers of Propecia to avoid birth defects in humans using drug.
  9. 9. How do you select appropriate animal as a model for the human system?  Look for genetic homology between animal and human systems.  In addition, identify animal that    Has short time between generations Can produce lots of offspring in each generation Can be easily maintained and manipulated in the laboratory
  10. 10. Matching animal systems as models for the human system System  Lung and cardiovascular Best animal model for human  Dog  Immune system  HIV and AIDS research  Mice  Monkey and chimpanzee
  11. 11. A model organism is a non-human species that is extensively studied to understand particular biological phenomena
  12. 12. Enviro Pig TM 12     Transgenic pigs express phytase in their salivary glands Phytic acid in the pig meal is degraded releasing phosphorus The phosphorus is absorbed by the pig. Normally the phytic acid/phosphorus complex passes through the pig and is excreted as waste  Pig waste is a major pollutant & can cause eutrophication of lakes & streams. YANAMALA VIJAY RAJ 1/20/2014
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  14. 14. transgenic fish 14 YANAMALA VIJAY RAJ 1/20/2014
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  16. 16. Laboratory rat A laboratory rat is a rat of the species Rattus norvegicus (brown rat) which is bred and kept for scientific research. Laboratory rats have served as an important animal model for research in psychology,medicine, and other fields. 16 YANAMALA VIJAY RAJ 1/20/2014
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  20. 20. Zebrafish
  21. 21. Zebrafish  Lots of genetic similarity to humans  Egg lends itself to genetic transfer  no need to implant an egg inside a donor mother for gestation.  Embryos are transparent, making it possible to study cell division under microscope from first hour of creation.  transplant gene into embryo  Because the genetics of zebrafish and humans are similar, they are ideal animal systems for determining whether a new drug induces genetic mutations
  22. 22. Easy to follow drug effect on embryo development under microscope, sinc e egg can mature outside female.
  23. 23. Homology Testing Oxford Grid human Dots represent similar genes Boxes with more than one dot represent conserved sequences
  24. 24. Exchanging genes between individuals Select for recombinant before somatic cells stop dividing Somatic cell of human Cloned in tissue culture Chromosome 5 Homologous Recombination (rare event) Targeted gene disruption or insertion Reconstructed embryo Look for effect of gene disruption or insertion on organ development
  25. 25. Homologous Recombination flawed gene Person 1 chromosome good gene Person 2 chromosome Mix chromosomes and promote DNA replication by mitosis. gccatt ccgtc cggtaa ggcag gccatt ccgtc cggtaa ggcag Exchange section of DNA on one chromosome with a section of DNA containing good gene on another chromosome. Offspring now has a copy of good gene from Person 2 in allele donated from Person 1
  26. 26. Reconstructed embryo Step 2: insert nucleus from transformed cell Egg divides to produce differentiated cells Genetically modified somatic cells Nucleus from somatic cell An new clone, a genetic copy of the donor, forms when the egg starts to divide Functional tissue or organ
  27. 27. Embryo Reconstruction EMBRYO RECONSTRUCTION BY TRANSPLANTATION OF THE DONOR INNER CELL MASS TO THE RECIPIENT BOVINE BLASTOCYST Embryo reconstruction for chimera production has been used in experiments oriented towards animal science such as the production of interspecies pregnancies in domestic animals . So far, chimeras have been obtained by the aggregation of the blastomeric or by inner cell mass transplantation . The aggregation of cell from embryos results in embryos with a more randomly distribution contribution of cells from each donor to the trophoblast and ICM. in their production of interspecific sheep-goat chimeras produced one kid by the injection of a goat ICM into a sheep blastocyst and one lamb from the reciprocal injection
  28. 28. Nuclear Transfer Step 1: Remove the nucleus from an egg egg Suction to hold egg Perforate egg with needle and withdraw intact nucleus
  30. 30.  Embryo twinning (conventional approach)  splitting embryos in half to produce artificially created twins commonly practiced in cattle industry today  limitation is that organisms being copied is unknown   you may or may not end up with an animal that has the desired characteristics and you have to wait until the animals is full-grown to find out.  Dolly was created from an adult cell-not an embryo  Dolly was an exact copy of an adult with known characteristics.  How is this done?
  31. 31. Cells collected from donor animal and put in a culture medium that keeps them alive but prevents their replication and stops gene expression. Egg of an animal has it’s nucleus (DNA) removed (enucleation) Nucleus of cultured somatic cells from donor animal are then inserted into a recipient animal’s egg next to its cytoplasm. Apply low-level electric charge and fuses with egg cytoplasm to produce a 1-cell cloned embryo. New cell containing egg behaves as if it were an embryonic cell rather than an adult cell. Cell division occurs just as it would in an ordinary fertilized egg. Transfer embryo to surrogate mother for gestation. Newborn will be genetically identical to donor
  32. 32. Successfully cloned species  Sheep  goat  pig  cow  endangered cow (gaur)  house cat
  33. 33. gaur
  34. 34. Limits of cloning  Viable cell is required  Success rate is still low  Dolly was successful only after 277 failed attempts   only 29 implanted embryos lived longer than 6 days Many clones are born with defects kidney problems  diabetes  crippling disabilities  old before their time-telomere length  Dolly was diagnosed with arthritis -premature aging? 
  35. 35. Cloning as a means of producing replacement body parts?  Idea is to reduce chance of cloned tissue from being rejected by original “parent”.  It would take years for clone to produce the organs to be used for transplant
  36. 36. Benefits of Cloning  Reduce variability of responses of a population being used to test new drugs, etc.  avoids confounding factor of different genetic predispositions  Preservation of endangered species  cloning pandas using common black bear as surrogate host.  Reduce time to produce new breeds of farm animals from 6-9 years 3 years
  37. 37. Early experiments on transgenic animals  A new gene was added to a cell grown in a tissue culture and the effects on that one cell were observed.  With the introduction of cloning, a gene could be added to many cells, and all the cells could be screened to see which one(s) contained the gene.  Each cell that contained the gene could then be used to grow a complete animal using cloning technology
  38. 38. Transgenic techniques  Retrovirus-mediated transgenesis  infect mouse embryo with retroviruses before the embryos are implanted into an animal for gestation. Retrovirus acts as a vector for the new DNA  size of new DNA is limited  viruses genetic material can interfere with embryo development  not very efficient  cell nucleus embryo retrovirus
  39. 39. Pronuclear injection  Introduction of foreign DNA at earliest possible stage of development of the zygote (fertilized egg)  Just before the egg and sperm cells join, DNA is injected into the nucleus of either cell.  Since the DNA is injected with a syringe, no vector is required and no vector genetic material is introduced that could complicate outcome
  40. 40. Embryonic stem cell method blastocyte  Embryonic stem cells are collected from inner cell mass of blastocytes  Cells are mixed with foreign DNA  some cells take up the foreign DNA and incorporate it into cell’s own DNA in the nucleus and are “transformed” Foreign DNA  Transformed cells are injected into the inner cell mass of the host blastocyte for differentiation and development Transformed cell blastocyte
  41. 41. Transgenics to make milk healthier for humans  Lactoferrin-protein that binds iron needed by human babies for development  introduce gene for this protein into cells of cow that are responsible for milk production  Human immune genes introduced into cows as a factory for human antibody production.
  42. 42. Transgenics as a means of deleting genes and their functions  Deleting a gene is a way of determining what its function is in the cell  Active gene is replaced with a gene that has no functional information  When the gene is “knocked out” by the useless DNA, the trait controlled by the active gene is eliminated from the animal .
  43. 43. Knockout Mice Knockout mice begin as embryonic stem cells with specifically modified DNA that has been prepared by recombinant techniques. The modification results in a nonsense mutation in the normal gene of the animal.
  44. 44. Homologous recombination within target gene Chromosome with normal gene Plasmid with useless DNA normal gene Useless DNA gccatt ccgtc cggtaa ggcag Recombination between vector gccatt ccgtc cggtaa ggcag and chromosome insert section of DNA of gene on vector into a section of DNA containing good gene on chromosome of stem cells. Chromosome is modified with a useless form of the gene. Look for a trait that has changed
  45. 45. Random insertion of useless gene at a location other than the target gene Chromosome with normal gene Vector with useless DNA normal gene Useless DNA Recombination between vector and chromosome gccatt ccgtc cggtaa ggcag gccatt ccgtc cggtaa ggcag Insert section of DNA of useless gene on vector into a section of chromosome that does not disrupt target gene. Chromosome is modified with a useless form of the gene at some other site than target gene
  46. 46. Transformed stem cell Knockout mouse with nonfunctional gene in all its differentiated somatic cells Blastocyte chimera Not all cells had the trait changed Need to crossbreed for 2 generations to get all cells to lose trait.
  47. 47. Producing human antibodies in animals  Antibodies are proteins whose structure gives it the ability to bind very specifically to other proteins Region of antigen protein that is specifically recognized and bound by antibody Antigen (Ag) Antibody (Ab)
  48. 48.  Antibodies could be designed that target and inactivate cancer cells in our bodies.  Myelomas: antibody-secreting tumors  Monoclonal Abs (mAb) are produced from myeloma cells that produce an Ab that reacts with only one region of an antigenic protein
  49. 49. Making cells that produce monoclonal antibodies The specific antibody is released into the culture medium and recovered Once a cell line is identified that produces an antibody against a specific antigen, it can be replicated and the cells frozen until needed to make the specific antibody
  50. 50. Review  Approaches to change genomes of animals  Nuclear transfer of genetically modified somatic cell into an egg. Rapid growth of organs for transplant into donor animal.  Nuclear transfer of somatic cell into egg implant into surrogate to produce viable organism (Dolly)  Retrovirus mediated genetic modification in animal genome.  Nuclear transfer of embryonic stem cell into egg. Implant into surrogate to produce viable organism