Rod Devenish; Week 5 MED1011; Biochemistry
Differentiation is from different gene expression. Fertilised egg is totipotent. Differentiated cell nucleus can retain totipotency and can act like a zygote to stimulate production of an organism. Reversing differentiation in plants is easier than animals, forms a clone. Tadpoles have been found to be able to form embryos, could not form frog from adult cell nucleus. Cloning done by fusing udder cells in early stages of division with enucleated egg using electrical pulses to mirror fertilisation and stimulate embryo development. After several cell divisions, early embryos were transplanted into surrogate mothers. This can be used to produce proteins in milk and cloned pigs for organ transplants.
Stem cells of inner cell mass are pluripotent. Can be cultured to differentiate as desired. Customised ESCs can be made transferring the nucleus from a normal patient cell to an enucleated egg (SCNT), collect ESCs from embryo that develops, can provide immunologically matched cell grafts for the patient, Not permitted by government is embryo development beyond 14 days, embryo implantation into a body or production of embryos by egg and sperm for research. Not good anyway as mitochondrial DNA comes from the egg so would not be a perfect match.
- SCNT not achieved for humans, NT is very inefficient, limited availability of eggs
Non specialised ES cells create teratomas (inappropriate expression of mixed cell types). SCNT requires destruction of human embryos, can use adult stem cells instead from bone marrow. Not easy to grow and have a limited lifespan. Useful because they show plasticity.
Somatic cells can be reprogrammed by culture with ES cells or defined factors to become dedifferentiated, pluripotent hESC line (induced pluripotent) caused by changing cell 'switches'. iPS not reset to embryo-like near tips and centres of chromosomes. iPS cells incorporate extra cancer causing genes and fewer tumour suppressor genes.
Human gene therapy is treatment or prevention of disease by gene transfer, involves gene addition currently not correction or replacement. Induced by vector which alters the genome.