future therapies in veterinary and human medicine

special properties of embryonic stem cells

• those taken from the morula stage or earlier are totipotent

• those taken from the inner cell mass at the blastocyst stage are pluripotent- can make all cells of body and some extraembryonic membranes but not placenta as this comes from the trophoblast

• can be immortal in the lab

how are embryonic stem cells derived?

• an embryo is fertilised in vitro and allowed to grow to the point where the inner cell mass is distinct from the trophoectoderm

• cells are extracted and placed into culture containing specific factors that keep them in an undifferentiated state

• so they continue to proliferte and can do so in these conditions indefinitely without senescing

• telomeres do not get shortened by repeated divisions unlike somatic cells

how are somatic stem cells derived

• isolated from adult tissues

• using protein markers present on cell surface 

• then amplified in culture

• do not proliferate indefinitely

• eg haemopoetic, bone marrow stromal

what are induced pluripotent stem cells?

• start as adult cells, usually fibroblasts from skin

• viral vectors introduced into these cells that carry genes that are normally expressed in the early developing embryo

• viral vectors use transcription and translation to produce proteins which instruct cells to believe that they are embryonic again

problems with embryonic stem cells

• ethical issues

• the little that we know about how to control differentiation comes from studies in the whole embryo, and applying these to ES cells in the dish can have mixed results

• eg mix of cell types resulted, and injecting them back into an organism can have deleterious effect

problems with adult stem cells

• not abundant

• difficult to identify and isolate

• have an immunological profile so person/animal will have an immune response

• required to take immunosuppressive drugs

• limited differentiation

problems with iPSCs

when you use viral vectors to introduce genes into cells there is a risk of mutation occurring

what is CRISPR-Cas gene editing

• a way to remove, add or alter dna in the cell

• guide RNA is made that is complementary to the piece of DNA code that needs to be edited

• guide RNA is attached to Cas9 enzyme

• this is introduced into the cell and the guide RNA attaches to DNA and Cas9 unwinds the double stranded DNA and cuts it

• the cell then repairs this break and usually inactives the gene in the process by introducing mutation

how could crispr cas be used to treat congenital disease

can be used in embryos to fix mutations that cause disease

problems with crispr cas

• ethical concerns as this alters the germ line in very early embryos

• possibility of off target effects so editing could happen on the wrong gene

• expensive so not affordable for large parts of human and animal population