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Somatic cell nuclear transfer
In genetics and developmental biology, somatic cell nuclear transfer (SCNT) is a laboratory strategy for creating a viable embryo from a body cell and an egg cell. The technique consists of taking a denucleated oocyte (egg cell) and implanting a donor nucleus from a somatic (body) cell. It is used in both therapeutic and reproductive cloning. In 1996, Dolly the sheep became famous for being the first successful case of the reproductive cloning of a mammal. In January 2018, a team of scientists in Shanghai announced the successful cloning of two female crab-eating macaques (named Zhong Zhong and Hua Hua) from foetal nuclei.
"Therapeutic cloning" refers to the potential use of SCNT in regenerative medicine; this approach has been championed as an answer to the many issues concerning embryonic stem cells (ESCs) and the destruction of viable embryos for medical use, though questions remain on how homologous the two cell types truly are.
Somatic cell nuclear transfer is a technique for cloning in which the nucleus of a somatic cell is transferred to the cytoplasm of an enucleated egg. After the somatic cell transfers, the cytoplasmic factors affect the nucleus to become a zygote. The blastocyst stage is developed by the egg to help create embryonic stem cells from the inner cell mass of the blastocyst. The first mammal to be developed by this technique was Dolly the sheep, in 1996.
Although Dolly is generally recognized as the first animal to be cloned using this technique, earlier instances of SCNT exist as early as the 1950s. In particular, the research of Sir John Gurdon in 1958 entailed the cloning of Xenopus laevis utilizing the principles of SCNT. In short, the experiment consisted of inducing a female specimen to ovulate, at which point her eggs were harvested. From here, the egg was enucleated using ultra-violet irradiation to disable the egg's pronucleus. At this point, the prepared egg cell and nucleus from the donor cell were combined, and then incubation and eventual development into a tadpole proceeded. Gurdon's application of SCNT differs from more modern applications and even applications used on other model systems of the time (i.e., Rana pipiens) due to his usage of UV irradiation to enucleate the egg instead of using a pipette to remove the nucleus from the egg.
The process of somatic cell nuclear transfer involves two different cells. The first being a female gamete, known as the ovum (egg/oocyte). In human SCNT experiments, these eggs are obtained through consenting donors, utilizing ovarian stimulation. The second being a somatic cell, referring to the cells of the human body. Skin cells, fat cells, and liver cells are only a few examples. The genetic material of the donor egg cell is removed and discarded, leaving it 'deprogrammed.' What is left is a somatic cell and an enucleated egg cell. These are then fused by inserting the somatic cell into the 'empty' ovum. After being inserted into the egg, the somatic cell nucleus is reprogrammed by its host egg cell. The ovum, now containing the somatic cell's nucleus, is stimulated with a shock and will begin to divide. The egg is now viable and capable of producing an adult organism containing all necessary genetic information from just one parent. Development will ensue normally and after many mitotic divisions, the single cell forms a blastocyst (an early stage embryo with about 100 cells) with an identical genome to the original organism (i.e. a clone). Stem cells can then be obtained by the destruction of this clone embryo for use in therapeutic cloning or in the case of reproductive cloning the clone embryo is implanted into a host mother for further development and brought to term.
Conventional SCNT requires the use of micromanipulators, which are expensive machines used to accurately manipulate cells. Using the micromanipulator, a scientist makes an opening in the zona pellucida and sucks out the egg cell's original nucleus using a pipette. They then make another opening to a different pipette to inject the donor nucleus. Alternatively, electric energy can be applied to fuse the empty egg cell with a donor cell containing a nucleus.
An alternative technique called "handmade cloning" was described by Indian scientists in 2001. This technique requires no use of a micromanipulator and has been used for the cloning of several livestock species. Removal of the nucleus can be done chemically, by centrifuge, or with the use of a blade. The empty egg is glued to the donor cell with phytohaemagglutinin, then fused using electricity. (If a blade is used, two fusion steps would be required: the first fusion is between the donor and an empty half-egg, the second between the half-size "demi-embryo" and another empty half-egg.)
Somatic cell nuclear transplantation has become a focus of study in stem cell research. The aim of carrying out this procedure is to obtain pluripotent cells from a cloned embryo. These cells genetically matched the donor organism from which they came. This gives them the ability to create patient specific pluripotent cells, which could then be used in therapies or disease research.
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Somatic cell nuclear transfer
In genetics and developmental biology, somatic cell nuclear transfer (SCNT) is a laboratory strategy for creating a viable embryo from a body cell and an egg cell. The technique consists of taking a denucleated oocyte (egg cell) and implanting a donor nucleus from a somatic (body) cell. It is used in both therapeutic and reproductive cloning. In 1996, Dolly the sheep became famous for being the first successful case of the reproductive cloning of a mammal. In January 2018, a team of scientists in Shanghai announced the successful cloning of two female crab-eating macaques (named Zhong Zhong and Hua Hua) from foetal nuclei.
"Therapeutic cloning" refers to the potential use of SCNT in regenerative medicine; this approach has been championed as an answer to the many issues concerning embryonic stem cells (ESCs) and the destruction of viable embryos for medical use, though questions remain on how homologous the two cell types truly are.
Somatic cell nuclear transfer is a technique for cloning in which the nucleus of a somatic cell is transferred to the cytoplasm of an enucleated egg. After the somatic cell transfers, the cytoplasmic factors affect the nucleus to become a zygote. The blastocyst stage is developed by the egg to help create embryonic stem cells from the inner cell mass of the blastocyst. The first mammal to be developed by this technique was Dolly the sheep, in 1996.
Although Dolly is generally recognized as the first animal to be cloned using this technique, earlier instances of SCNT exist as early as the 1950s. In particular, the research of Sir John Gurdon in 1958 entailed the cloning of Xenopus laevis utilizing the principles of SCNT. In short, the experiment consisted of inducing a female specimen to ovulate, at which point her eggs were harvested. From here, the egg was enucleated using ultra-violet irradiation to disable the egg's pronucleus. At this point, the prepared egg cell and nucleus from the donor cell were combined, and then incubation and eventual development into a tadpole proceeded. Gurdon's application of SCNT differs from more modern applications and even applications used on other model systems of the time (i.e., Rana pipiens) due to his usage of UV irradiation to enucleate the egg instead of using a pipette to remove the nucleus from the egg.
The process of somatic cell nuclear transfer involves two different cells. The first being a female gamete, known as the ovum (egg/oocyte). In human SCNT experiments, these eggs are obtained through consenting donors, utilizing ovarian stimulation. The second being a somatic cell, referring to the cells of the human body. Skin cells, fat cells, and liver cells are only a few examples. The genetic material of the donor egg cell is removed and discarded, leaving it 'deprogrammed.' What is left is a somatic cell and an enucleated egg cell. These are then fused by inserting the somatic cell into the 'empty' ovum. After being inserted into the egg, the somatic cell nucleus is reprogrammed by its host egg cell. The ovum, now containing the somatic cell's nucleus, is stimulated with a shock and will begin to divide. The egg is now viable and capable of producing an adult organism containing all necessary genetic information from just one parent. Development will ensue normally and after many mitotic divisions, the single cell forms a blastocyst (an early stage embryo with about 100 cells) with an identical genome to the original organism (i.e. a clone). Stem cells can then be obtained by the destruction of this clone embryo for use in therapeutic cloning or in the case of reproductive cloning the clone embryo is implanted into a host mother for further development and brought to term.
Conventional SCNT requires the use of micromanipulators, which are expensive machines used to accurately manipulate cells. Using the micromanipulator, a scientist makes an opening in the zona pellucida and sucks out the egg cell's original nucleus using a pipette. They then make another opening to a different pipette to inject the donor nucleus. Alternatively, electric energy can be applied to fuse the empty egg cell with a donor cell containing a nucleus.
An alternative technique called "handmade cloning" was described by Indian scientists in 2001. This technique requires no use of a micromanipulator and has been used for the cloning of several livestock species. Removal of the nucleus can be done chemically, by centrifuge, or with the use of a blade. The empty egg is glued to the donor cell with phytohaemagglutinin, then fused using electricity. (If a blade is used, two fusion steps would be required: the first fusion is between the donor and an empty half-egg, the second between the half-size "demi-embryo" and another empty half-egg.)
Somatic cell nuclear transplantation has become a focus of study in stem cell research. The aim of carrying out this procedure is to obtain pluripotent cells from a cloned embryo. These cells genetically matched the donor organism from which they came. This gives them the ability to create patient specific pluripotent cells, which could then be used in therapies or disease research.