Epigenetics: Nuclear transplantation & Reprogramming of the genome
Dec 27, 2015
Epigenetics:Nuclear transplantation &
Reprogramming of the genome
Historical perspectives
• Big question: ‘nuclear cloning’ is possible? (genome of differentiated cells is identical to
that of undifferentiated cells?)• New concept: ‘Reprogramming’ (somatic to
embryonic epigenetic state)• Earlier studies with amphibian (frog eggs) Later studies with mammals (mouse eggs)
Nuclear transfer procedure (frog)
Nuclear transfer procedure (mouse)
Earlier attempts: zygotes + nuclei fromcleavage stage donor embryos
Some success in farm animals not inmouse : lambsTransition time difference: maternal tozygotic transcription
‘Dolly’ cloning: mammary gland donor1st somatic cell nuclear transfer (SCNT)
More than 15 mammalian species cloned
Phenotype of cloned animals
More differentiated-stage cellsderive much less success!
Frog nuclear transfers were successful up to tadpole stage!
Phenotype of cloned animalsThe majority fails after implantation
G0 or G1 –phase donor cells are moresuccessful upto blastocyst than S-phaseES or EC cells.
But more success rates in ES or EC beyond the blastocyst stage.
Cloned animals (survivors) likely havesome defects that are responsible foradult-stage health problems.
Large offspring syndrome(large fraction of placenta-specific genesare changed in terms of their expression levels)
Gametogenesis reprogramming isimportant for placenta genes
Reprogramming of terminally differentiated cells (monoclonal mice)
A little loss of genomic complement is not a problem for cloning!
Reprogramming of terminally differentiated cells (olfactory neuron)
Medical implications of nuclear transplantation
Reproductive cloning
vs
Therapeutic cloning
Medical implications of nuclear transplantation (demonstration)
iPS (Induced Pluripotent Stem) cells
• three factors (Oct4, Sox2, Klf4) can transform adult cells into stem cells.
• does not require early-stage embryos or cells from patients
iPS (Induced Pluripotent Stem) cells