51. Organismal cloning of plants and animals. Embryonic and adult stem cells.

Question 1

Organismal cloning of whole plants

Answer 1

• In plants, mature cells can “dedifferentiate” and then give rise to all the specialized cell types of the organism; any cell with this potential is said to be totipotent.

Applications:
* For orchids, cloning is the only practical means of producing
new plants.
* In other cases, cloning has been used to reproduce a plant with valuable characteristics, such as resistance to plant pathogens.

Question 2

Organismal cloning of animals

Answer 2

• approach was to remove nucleus of an egg (creating an enucleated egg) and replace it with the nucleus of a differentiated cell, a procedure called nuclear transplantation,
  now more commonly called somatic cell nuclear transfer.

Gurdon’s experiment in 1970s
- nuclei of frog eggs are destroyed by exposing them to UV light. the nuclei are transplanted from cells of frog embyos and tadpoles into enucleated eggs
- result - when transpanted nuclei came from an early embryo, the cells of which are relatively undifferentiated, most
of the recipient eggs developed into tadpoles. But when nuclei came from the fully differentiated
intestinal cells of a tadpole, fewer than 2% of the eggs developed into normal tadpoles, and most of the embryos stopped developing at a much earlier stage.
- Conclusion: The nucleus from a differentiated frog cell can
direct development of a tadpole. However, its ability to do so
decreases as the donor cell becomes more differentiated.

Question 3

Embryonic and Adult Stem Cells

Answer 3

• Stem cells can be isolated from early embryos at the blastula or blastocyst stage.
• Embryonic stem cells can reproduce indefinitely in culture.
• Depending on culture conditions, embryonic stem cells can differentiate into various specialized cells, including eggs and sperm.
• The adult body has stem cells to replace non-reproducing specialized cells as needed.
• Adult stem cells cannot give rise to all cell types in the organism, unlike embryonic stem cells.

Embryonic Stem Cells – a potential for medical applications:
1. Repair of damaged or diseased organs - therapeutic cloning:
- insulin-producing pancreatic cells for people with type 1 diabetes
- certain kinds of brain cells for people with Parkinson’s disease or Huntington’s disease.
- adult stem cells from bone marrow for bone marrow transplants serve as a
source of immune system cells in patients with nonfunctional immune cells due to genetic disorders or radiation treatments for cancer.
2. Human cloning – ethical issues

Can a fully differentiated human cell be “deprogrammed” to become a stem cell?

Yes, fully differentiated human cells can be “deprogrammed” into stem cells known as induced pluripotent stem (iPS) cells by expressing a specific set of transcription factor genes or treating with these proteins directly. This reprogramming process resets the cells to an embryonic-like state, enabling them to differentiate into various cell types