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