Science in the NewsAdapted by your

teacher Ms. Boehm

Stem Cells

• Where do stem cells come from?

• What is a stem cell?

• What are stem cells good for?

Stem Cell

2. Capable of self-renewal(One daughter cell is like parent)

1. Capable of dividing and making new cells of many types

Differentiation: the process by which a cell undergoes a change to become a specialized cell type

Differentiation occurs step-by-step

Stem CellsPluripotent cell (Embryonic Stem Cell)

Differentiation occurs step-by-step

Stem CellsPluripotent cell (Embryonic Stem Cell)

Multipotent cell (Adult Stem Cell)

Adult Mouse

Embryonic Stem Cells Bridge the Gap from theFertilized Egg to the Fully Formed Organism

Fertilized Egg

(“Totipotent”)

Embryo

(Cell Division and Differentiation)

(“Pluripotent” Cells)

Pancreas cell

Lens cell

Muscle cell

IMPORTANT!!!!!Each of these different

cell types has the same DNA

How do cells with the same DNA end up so different?

Gene A Gene B

MuscleCell

Gene A is on

Gene B is off

X

LensCell

Gene A is off

Gene B is on

PancreasCell

Gene A is on

Gene B is on

Protein A

DNA X

Where do stem cells come from?

Embryonic Stem Cells1. Pluripotent2. Derived from the blastocyst 3-5 days after fertilization

ZygoteZygoteBlastocystBlastocyst

++

SpermSperm

EggEgg

FetusFetus

inner cell mass (embryo)

trophoblast (placenta)

Embryonic Stem Cells

A blastocyst contains 200-250 cells.The inner cell mass is only 30-34 cells

There are 10,000,000,000,000 cells in a human adult

1. Obtain cells from blastocyst

Inner cell mass

2. Grow cells on a dish in the lab

ESCs grow on “feeder” cells

• Provides nutrients to stem cells

• Structural support for growth

3. Cells grow in the dish

Actual stem cells seen under microscope

Able to self-renew

ESCs have the potential to produce different types of cells

Muscle Skin BloodLiver

And Where are the adult stem cells?

AdultstemcellsNeural Brain cell types

Skin Skin and hair

Gut Gut derivatives

eye Eye cell types

Blood & marrow Blood cell types

Each type of adult stem cell is found in the tissue it makes.

• mixed among the differentiated cells in that tissue

Different Types of Stem Cells: What and Where?

Embryonic Adult

• Isolate from inner cell mass of embryo (blastocyst stage)

• Found in from adult tissue (but for most types we don’t know how to find them)

• Can make all cell types (TOTIPOTENT)

• Only make certain cell types (MULTIPOTENT)

Potential:

How they are obtained:

What are stem cells good for?

Replacement is permanent! (stem cells are self-maintaining)

Stem cells could replace dead or damaged cells

Stem cells could be transplanted directly into diseased tissue where they would become the desired cell type

or

Stem cells could be coaxed into specializing in the lab and then transplanted as differentiated tissue

A bone marrow transplant isan adult stem cell transplant

Leukemia

A bone marrow transplant isan adult stem cell transplant

1. Stem cells contribute to all blood cell types

2. After several months, the new cells still populate blood

Leukemia(remove bone marrow)

Blood Cells Regenerated

Implant with Blood Stem Cells

Challenges of using adult stem

cells

Challenge 1: Not yet found in all tissues

Pancreas

Challenge 2: Not easily accessible in all tissues

Brain

Muscles

How are we going to get stem cells from the brain of the patient??

Challenge 3. Rare & Difficult to isolate

Need “markers” to differentiate stem cells from other types of cells

Embryonic vs. Adult Stem Embryonic vs. Adult Stem CellsCells

Embryonic Stem Cells

• Technical difficulties: How to direct specific differentiation

• Controversy: Ethical considerations

Adult Stem Cells

• Technical difficulties: Need to improve isolation techniques and optimize culturing conditions

Embryonic stem (ES) cells may be used to treat deteriorating brain cells

Parkinson’s Disease: Selective death of subset of neurons

Mouse model of Parkinson’s disease

Inject mouse ES cellsInto diseased brain

2. Still in experimental infancy, but shows much promise for many diseases.

1. Could be used to treat Alzheimer’s, Huntington’s,spinal cord injury, etc…

Partial replacement of lost neurons

Where do the blastocysts come from?

In vitro fertilization

• Aim to help infertile couples conceive children

• Egg is fertilized with sperm in the lab

Zygote Blastocyst

Sperm

Egg

Fertilization

LAB

In vitro fertilization

Blastocyst

Implanted back into woman

Frozen

Embryonic stem cells

Problem of immune rejection• Each person has own unique set of DNA

• Body’s immune system rejects cells that do not belong to the individual

• Need to match donor cells/tissues/organs to recipient

• Stem cells used must be genetically compatible with patient

• Embryonic stem cell lines derived from IVF will not be compatible Somatic Cell Nuclear Transfer (SCNT) = THERAPEUTIC CLONING

Somatic cell nuclear transfer (SCNT)

• Somatic Cell = Any cell of the body, except sperm and egg

• Nuclear Transfer = Moving the genetic material (DNA) of one cell to another

• Nucleus of an egg is removed and replaced with the DNA of an adult cell

• Creates patient-specific ES cell line

Therapeutic cloning

vs.

Reproductive cloning

What is cloning?

• Clones = INDIVIDUALS that are genetically identical to another

Identical twins are clones

• Clones = CELLS that are genetically identical to another

=

CLONINGCLONING

Need to be implanted into a surrogate mother

“Personalized”Stem cells for tissue

therapy

REPRODUCTIVE CLONING

THERAPEUTIC CLONING

1. Remove nuclear DNA from egg

1. Remove nuclear DNA from egg

2. Insert DNA from donor into egg

2. Insert DNA from donor into egg

“Personalized”Stem cells for tissue

therapy

THERAPEUTIC CLONING

Advanced Cell Technology, Worchester, Massachusetts