Somatic Cell Nuclear Transfer (SCNT) and Cloning


Due to the rapid advances in stem cell research – and given impetus due to political restrictions on federal funding using embryos (Loike and Fischbach 2009), several new sources have been developed to obtain human embryonic stem cells (ESC), or ESC-like cells. The fourth source for acquiring human embryonic stem cells is through a technology referred to as somatic cell nuclear transfer (SCNT), sometimes referred to as cloning (research or therapeutic cloning; reproductive cloning). Due to the rapid advances in stem cell research – and given impetus due to political restrictions on federal funding using embryos (Loike and Fischbach 2009) - this is one of several new sources THAT have been developed in the laboratory to obtain human embryonic stem cells (ESC), or ESC-like cells.

Like normal reproduction, somatic cell nuclear transfer (SCNT) starts with an egg or oocyte. But here the nucleus of the egg is removed. Then the nucleus from a somatic (skin) cell is transferred into the enucleated egg which would be analogous to the sperm entering the oocyte. As this develops into a blastocyst, cells from the inner cell mass can be isolated and purified to serve as a source for pluripotent stem cells. See **Module 4 - Somatic Cell Nuclear Transfer** for a more detailed discussion on SCNT.




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Hochedlinger and Jaenisch (2003) New England Journal of Medicine





Cloning Distinctions

It is essential to know the difference between reproductive cloning and therapeutic cloning. As you can see from the figure above, the process is the same with one important difference.

With reproductive cloning (the middle diagram) where the intent is to create a baby, the embryo would be taken from the Petri dish and placed into a uterus and would be allowed to gestate through a normal pregnancy. The born child would be viewed biologically as an identical twin of the donor of the somatic cell.

Thought Questions


What would be the psychological challenges faced by the parents who used SCNT and IVF to create an identical twin of an older sibling?

What might be the expectations of the younger twin in aspiring to achieve the same educational and athletic milestones of the older sibling?



The purpose of therapeutic cloning is to provide stem cells for medical purposes. It is preferable to avoid the term therapeutic and refer to this form of cloning as “research” cloning because to date, we are far from having reached any therapeutic use. Additionally, because it may be years until we do see some therapeutic results, it is best to refer to this process as somatic cell nuclear transfer (SCNT).

Reproductive cloning at the present time is considered unethical. Therefore, of absolute importance, in somatic cell nuclear transfer (SCNT) (research/therapeutic cloning), the embryo is allowed to develop only until the 14th day. The 14-day embryo would never be placed into a uterus.

Induced pluripotent stem cells (iPS) are a fifth process for obtaining stem cells. In this process, the insertion of specific transcription factors into differentiated cells converts them to pluripotent stem cells without the use of an ovum. We present iPS technologies in much more detail in **Module 5**.

Is this where the promise lies? If these stem cells can be coaxed to become whatever the need is for the donor, be it nerve, cardiac muscle, or pancreatic islet cells, the derived cells could be given to the donor without any risk of rejection as the DNA would be identical and there would be no immune response.

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