Updated: Jul 7, 2022
For years, scientists and citizens wondered about cloning and even though it sounds otherworldly, scientists have found a way to clone. It may not be what we expected when we were kids, but it still is cloning. With recent news shining a light on the discovery of a mummified baby woolly mammoth, scientists have started to think about cloning mammoths using the samples from the mammoth. Even though it is still uncertain, researchers still think they can manage to bring mammoths back to life in the early future.
Cloning, in text, involves growing a new organism from a single cell of an old organism. This requires that the cell used for cloning needs to be able to revert to its "primitive" state, typical of an egg cell. They need to be able to replicate and differentiate. Cloning, or somatic cell nuclear transfer (SCNT), is also used to produce Dolly the sheep, the first animal to be produced as a genetic copy of another adult.
During the process of cloning Dolly the sheep, the nucleus of an egg cell was removed and replaced by the nucleus of a cell from the mammary gland of an adult ewe. This nucleus contained the ewe’s DNA. After being inserted into the egg, the adult cell nucleus was then reprogrammed by the host cell. The egg was artificially stimulated to divide and behave in a similar way to that of an embryo fertilized by sperm. After many divisions in culture, this single cell forms a blastocyst, an early-stage embryo with about 100 cells, with almost identical DNA to the original donor who provided the adult cell, which is a genetic clone.
At this stage, there are two different ways of cloning: reproductive cloning and therapeutic cloning. To produce Dolly, the cloned blastocyst was transferred into the womb of a recipient ewe where it developed, being born into its status of the world’s most famous lamb. This specific process, enabling the production of a living duplicate of an existing animal, is commonly called reproductive cloning. Early experiments with cloning plants showed that individual somatic cells, cells that do not form pollen or egg, could form complete, new clonal plants, indicating that the somatic cells had no irreversible changes in their genome compared to the original fertilized egg cell. As vertebrate animals progressed through embryonic development, birth, and aging, their somatic cell nuclei became “programmed” to differentiate into specialized cells, rather than to support embryonic development. We now know that this programming involves reversible chromatin modification, restricting which genes can be expressed in differentiated cells.
On the other hand, in therapeutic cloning, the blastocyst is not transferred to a womb. Instead, embryonic stem cells are isolated from the cloned blastocyst. These stem cells are genetically matched with the donor organism which can be used for studying a genetic disease. For example, stem cells could be generated using the nuclear transfer process described above, with the donor adult cell coming from a patient with diabetes or Alzheimer’s. The stem cells could be studied in the laboratory to help researchers understand what goes wrong in diseases like these. Another long-term hope for therapeutic cloning is that it could be used to generate cells that are genetically identical to a patient. A patient transplanted with these cells would not suffer the problems associated with rejection. To this date, no human embryonic stem cell lines have been derived using therapeutic cloning, so both these options remain very much possible in the future.
The human body is quite limited in its ability to regenerate or repair injuries or diseases that affect critical organs such as the brain, heart, and pancreas. Tissue and organ regeneration and gene therapy require a source of cells that can differentiate into the desired types of cells, for the life of the patient. Adult humans have distinct reservoirs of stem cells, which are located in different parts of the body, stem cells, by definition, can continue to divide and both replace themselves and produce progeny cells that differentiate into new blood and immune system cells, skin cells, muscle cells, or cells that line the gut and airways. But these adult stem cells are difficult to obtain from a patient, and they are restricted in the types of cells or tissues they can form. For example, the stem cells in bone marrow can generate both white and red blood cells, but not skin cells or new brain cells or heart muscle, nor pancreatic beta islet cells.
Scientists and professors are working hard to reach conclusions and learn more about cloning and stem cells. The significant journey that comes with cloning research continues to develop like any other scientific project. But the hope and want of bringing back the extinct creatures to life is the most important thing for scientists right now. Science says there is a chance we will see mammoths after almost 10,500 years.
"Cloning and Stem Cells." Biological Principles, bioprinciples.biosci.gatech.edu/module-5-integrative-health/02-cloning-and-stem-cells/.
"Cloning and Stem Cells." LibreTexts, bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Supplemental_Modules_(Molecular_Biology)/Cloning_and_stem_cells.
"What Is Cloning, and What Does It Have to Do with Stem Cell Research?"