Human Development

• starts with just 1 cell – the fertilized egg.

• This cell divides to produce 2 ‘daughter cells’.

• These daughters divide, and their daughters divide again, and so on.

• There are a great many steps needed to form an adult body, or even a baby. Along the way, lots of different types of cells must be made.

Stem Cells

• Stem cells are different from other cells of the body because stem cells can both:

1)Self-renew: Make copies of themselves • AND • 2) Differentiate: Make

other types of cells – specialized cells of the body.

Gene Expression

Remember:• Unlike gametes (egg and sperm), all other cells

(somatic cells) have the same DNA content and the same genes

• Since DNA RNA protein, then how can we account for different protein patterns in different types of cells?– The expression pattern of certain genes within

different types of cells is NOT identical. Genes are turned on and off.

All stem cells are not alike….

• Potency: describes flexibility to become other types of cells– Pluripotent: can form

almost any type of cell (embryonic stem cells)

– Multipotent: can become some but not all types of cells (adult stem cells)

Embryonic Stem Cells

• Taken from inside the blastocyst, a very early stage embryo.

• The blastocyst is a ball of about 50-100 cells and it is not yet implanted in the womb.

Embryonic stem (ES) cells:What they can do

embryonic stem cells

PLURIPOTENT

all possible types of specialized cells

differentiation

Adult Tissue Stem Cells• We all have stem cells in our

bodies all the time. • They replace cells that are

damaged or used up. • Adult Tissue stem cells are more

limited than embryonic stem cells.

• Adult Tissue stem cells can ONLY make the kinds of cell found in the tissue they belong to. – Blood stem cells cell found in

the blood. – Muscle stem cells muscle cells.

Tissue stem cells:What they can do

MULTIPOTENT

blood stem cell

found in bone marrow

differentiation

only specialized types of blood cell:red blood cells, white blood cells,

platelets

Induced Pluripotent Cells (iPS)• In 2006, scientists discovered that it is possible to transform skin

cells from a mouse into cells that behave just like embryonic stem cells.• In 2007, researchers did this with human cells too.• The new stem cells that are made in the lab are called induced

pluripotent stem cells. • Just like embryonic stem cells, they can make all the different

types of cell in the body – so we say they are pluripotent.

Why are they exciting?!?!?!

Researchers hope that one day they might be able to use iPS cells to help treat genetic diseases like Parkinson’s or Alzheimer’s. They hope to:

1)Take cells from the body - like skin cells - from a patient2)Make iPS cells3)Use those iPS cells to grow the specialized cells the

patient needs to recover from the disease, e.g. certain brain cells. These cells would be made from the patient’s own skin cells so the body would not reject them.

CloningThere are two VERY different types of cloning:

Reproductive cloning

Cells are use to make two identical individuals

Very difficult to do

Illegal to do on humans

Therapeutic cloning

Cells do not become an organism but stay in Petri Dish

Could be key to fix defective genes

Somatic Cell Nuclear Transfer (SCNT)

1. Take a body cell and extract nucleus

2. Take an egg cell and extract nucleus

3. Put nucleus from body cell into egg cell

4. Implant in womb (reproductive cloning) or cells can remain in culture (therapeutic cloning)

Pros versus Cons of Stem Cell Research

Pros• Understanding genetic diseases and finding possible cures

• Tissue Engineering (“artificial parts”)

• Patient Specific so no risk of rejection

• Creation of models that can be test on

Cons•Ethical considerations

•Genetic modification

•Uncertain future/outcomes

•Safety