Early Embryonic Development

Stem Cells

Stem Cells – Part 1The Information

What are they?Where do we get them from?

Are they all the same?Why are we interested in them?

• Correct stimulus is given to unspecialised cells e.g. a chemical stimulus

• Some genes are switched on and become active; other genes are switched off

• m-RNA is made from the active genes• m-RNA moves to the ribosomes; the ribosomes

read the m-RNA and the appropriate protein is made

• The protein can permanently alter the structure and function of cells

How cells become specialised

Stem Cells – What are they?

.A type of source or master cell that can .........

Undifferentiated cellsWhich keep dividingAnd can give rise to other cell types

Potency How much stem cells differentiate is called potency Stem cells vary in their potency:• Totipotent: can give rise to any cell and so can

produce a whole organism• Pluripotent: potential to develop into many cell

types but not all of them.• Multipotent: cells retain the capacity to make a

few types of cell • Unipotent: make one type of cell e.g. Skin cells

What are they and where are they found?

Timeline of development• Day 1: Fertilisation – a zygote is formed Series of rapid cell divisions No increase in size

• Day 5: Blastocyst – a hollow ball of cells Outer layer Placenta Inner 50 cells Embryo

• Week 12: Fully differentiated foetus.

Zygote: Totipotent stem cells

Blastocyst: Pluripotent stem cells

Foetus and adult: Mulitpotent and unipotent stem cells

Stem cells and their use in medicine

Sources of stem cells:•Multipotent cells from adults•Spare embryos from IVF (pluripotent)•Umbilical cord stem cells•Therapeutic cloning or admixed embryos

http://www.wellcome.ac.uk/About-us/Policy/Spotlight-issues/Human-Fertilisation-and-Embryology-Act/Humanadmixedembryos/index.htm

Different view points

Just a last point....

Ethical considerations

• Where do you stand on the issue of using embryonic stem cells?

• What are the advantages and disadvantages of using them in research?