Somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) places the nucleus of a body cell into an egg whose own nucleus has been removed. The egg can then be stimulated to develop, producing an embryo or, in some protocols, stem cells.

Enucleation: The removal of a cell's nucleus, often by microsurgery. SCNT begins by removing the egg's nucleus while preserving its cytoplasm.
Dolly (sheep): A sheep born in 1996, the first mammal cloned from an adult somatic cell. Dolly demonstrated that an adult-cell nucleus could support development to birth.
Hans Spemann: A German embryologist whose experiments shaped early developmental biology. His 1938 proposal anticipated transferring a nucleus into an enucleated egg.
Embryo splitting: The division of an early embryo to produce genetically similar embryos. Unlike SCNT, it duplicates an embryo without replacing an egg's nucleus.
Oocyte: An immature female germ cell that can mature into an egg. An oocyte supplies the cytoplasm that reprograms the transferred nucleus.
Reproductive cloning: The production of an organism genetically matched to a donor through cloning. SCNT can produce an embryo transferred to a uterus to attempt a live birth.
Robert Briggs: An American embryologist who pioneered nuclear transplantation in amphibians. With Thomas King, he demonstrated nuclear transfer in frog embryos in 1952.
Artificial insemination: The introduction of sperm into the female reproductive tract by a medical or technical procedure. It uses fertilization by sperm rather than transfer of a somatic nucleus.
Nuclear reprogramming: The resetting of gene activity and cell identity in a nucleus. Egg cytoplasm must reverse many specialized features of the donor nucleus.
Therapeutic cloning: The creation of cloned embryos to derive stem cells, rather than to produce offspring. This use of SCNT aims to generate stem cells carrying a donor's nuclear genome.

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