Epigenetics: Nuclear transplantation & Reprogramming of the genome.

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Epigenetics: Nuclear transplantation & Reprogramming of the genome

Transcript of Epigenetics: Nuclear transplantation & Reprogramming of the genome.

Page 1: Epigenetics: Nuclear transplantation & Reprogramming of the genome.

Epigenetics:Nuclear transplantation &

Reprogramming of the genome

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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)

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Nuclear transfer procedure (frog)

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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

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Phenotype of cloned animals

More differentiated-stage cellsderive much less success!

Frog nuclear transfers were successful up to tadpole stage!

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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

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Reprogramming of terminally differentiated cells (monoclonal mice)

A little loss of genomic complement is not a problem for cloning!

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Reprogramming of terminally differentiated cells (olfactory neuron)

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Medical implications of nuclear transplantation

Reproductive cloning

vs

Therapeutic cloning

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Medical implications of nuclear transplantation (demonstration)

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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

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iPS (Induced Pluripotent Stem) cells