Somatic Cell Nuclear Transfer (SCNT)
In the previous chapters, we learned about somatic cells (regular body cells) and stem cells (unspecialized master cells). Somatic Cell Nuclear Transfer (SCNT) is a highly advanced laboratory technique that brings these two concepts together.
In simple terms, SCNT is a method used by scientists to create a viable embryo from a regular body cell and an egg cell. This technique is the foundation of both reproductive cloning (like creating Dolly the sheep) and therapeutic cloning (creating embryonic stem cells for medical treatment).
Here is a step-by-step breakdown of how the SCNT process works.
1. Isolation of Somatic Cell
The process begins by selecting the organism that scientists want to clone or study. A regular somatic cell, such as a skin cell or an udder cell, is gently extracted from this donor organism. This somatic cell contains the complete, diploid genetic code (DNA) of the donor. Scientists isolate the nucleus from this cell, as the nucleus is the control centre holding the DNA.
2. Egg Cell Donation
Next, scientists need an unfertilized egg cell (also called an oocyte). This is collected from a female donor of the same species. Under a microscope, researchers use a microscopic needle to carefully suck out the original nucleus of this egg cell. An egg cell with its nucleus removed is called an enucleated egg. It now acts as an empty vessel.
3. Nuclear Transfer
In this crucial step, the nucleus isolated from the donor’s somatic cell is inserted into the empty egg cell. To make the newly inserted nucleus fuse properly with the egg fluid, scientists apply a very mild electrical current.
4. Cell Division and Blastocyst Formation
The mild electrical shock does more than just fuse the cell; it tricks the egg into behaving as if it has just been naturally fertilized by a sperm. The cell “wakes up” and begins to divide. It divides from one cell into two, then four, then eight, and so on. After a few days in the laboratory, it forms a hollow ball of about 100 unspecialized cells. This early-stage embryo is called a blastocyst.
5. Implantation or Stem Cell Harvesting
What happens to the blastocyst depends entirely on the purpose of the experiment:
- For Reproductive Cloning: If the goal is to create a living animal clone, the blastocyst is implanted into the womb of a surrogate mother. The surrogate carries the pregnancy to term, and the resulting offspring is a genetic twin of the original somatic cell donor. This is how India’s National Dairy Research Institute (NDRI) successfully cloned the buffalo named Garima.
- For Therapeutic Cloning: If the goal is medical research, the blastocyst is not implanted into a womb. Instead, scientists carefully open the blastocyst in the laboratory to harvest embryonic stem cells. These stem cells are a perfect genetic match to the patient who donated the somatic cell, meaning they can be used to grow replacement tissues that the patient’s body will not reject.
Significance of SCNT
SCNT is a major breakthrough in modern biology. It proves that the genetic material inside a mature, specialized adult cell can be entirely “reprogrammed” back to an embryonic state. While human reproductive cloning using SCNT is strictly banned worldwide due to ethical concerns, its use in animal conservation and therapeutic stem cell research holds tremendous promise for the future of medicine.
