Advanced Placement Advanced Placement Biology Biology

and and Stem CellsStem Cells

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Stem Cells The Nature of Stem Cells and Embryology

What is a Stem Cell?• A cell that has the ability to continuously

divide and differentiate (develop) into various other kind(s) of cells/tissues

• Stem cells are different from other cells of the body in that they have the ability to differentiate into other cell/tissue types.

• This ability allows them to replace cells that have died. With this ability, they have been used to replace defective cells/tissues in patients who have certain diseases or defects.

Stem Cell ApplicationsStem Cell Applications• Tissue repair

nerve, heart, muscle, organ, skin Regenerate spinal cord, heart tissue or any

other major tissue in the body.• Cancers

Studies show leukemia patients treated with stem cells emerge free of disease

Injections of stem cells have also reduces pancreatic cancers in some patients.

• Autoimmune diseases diabetes, rheumatoid arthritis, MS

Click on the picture to watch a video on the skin shooter

Replace Skin

Kinds of Stem CellsKinds of Stem Cells

Stem cell Stem cell typetype DescriptionDescription ExamplesExamples

TotipotentTotipotent Each cell can develop Each cell can develop into a new individualinto a new individual

Cells from early (1-Cells from early (1-3 days) embryos3 days) embryos

PluripotentPluripotent Cells can form any (over Cells can form any (over 200) cell types200) cell types

Some cells of Some cells of blastocyst (5 to 14 blastocyst (5 to 14 days)days)

MultipotentMultipotentCells differentiated, but Cells differentiated, but can form a number of can form a number of other tissuesother tissues

Fetal tissue, cord Fetal tissue, cord blood, and adult blood, and adult stem cellsstem cells

Illustration by Matt Bohan, 2007

Embryonic Stem cells are obtained from In-Vitro Fertilization embryos that were not used - http://www.news.wisc.edu/packages/stemcells/illustration.html

This cellCan form the

Embryo and placenta

This cellCan just form the

embryo

Fully mature

EMBRYONIC STEM CELLSEMBRYONIC STEM CELLS

Blastocyst

http://stemcells.nih.gov/info/basics/ "Image courtesy of NIH resource for stem cell research"http://en.wikipedia.org/wiki/Image:Blastocyst_English.svg

Umbilical Cord Stem Cells

• Also Known as Wharton’s Jelly• Adult stem cells of infant origin• Less invasive than bone marrow• Greater compatibility• Less expensive

• Skin • Fat Cells• Bone marrow• Brain• Many other organs

& tissues

Adult Stem CellsAn undifferentiated cells found among specialized or differentiated cells in a tissue or organ after birth

Umbilical Cord Stem Cells

Three important functions:

1. Plasticity: Potential to change into other cell types like nerve cells

2. Homing: To travel to the site of tissue damage

3. Engraftment: To unite with other tissues

STEM CELLS HAVE ALSO BEEN FOUND IN “MATURE” ORGANS

Illustration by Matt Bohan, 2007

Differences between embryonic stem cells and adult stem cells

• They have different self-renewal capabilities– Embryonic stem cells: near indefinite self-renewal– Adult stem cells: limited self-renewal

• They have different differentiation potentials– .Embryonic stem cells: differentiate into all cell types in an

organism– Adult stem cells: differentiate into restricted cells types.

• They differ in how they respond to external stimuli– Embryonic stem cells are readily to change upon stimulation– Adult cells emphasize on stability and need to be activated by

cues, e.g. injuries.

PROS AND CONS OF EACH TYPEPROS AND CONS OF EACH TYPE

• EMBRYONIC– CELL LINES LAST

AND LAST AND LAST

– MULTIPOTENT

– EASY TO FIND

– ETHICAL ISSUES - WHEN DOES LIFE BEGIN?

• ADULT – CELL LINES DO

NOT LAST

– NOT MULTIPOTENT

– HARD TO LOCATE

– NO ETHICAL ISSUES

Why the Controversy Over Stem cells?Why the Controversy Over Stem cells?

• Embryonic Stem cells are derived from extra blastocysts that would otherwise be discarded following IVF.

• Extracting stem cells destroys the developing blastocyst (embryo).

-Questions for Consideration-• Is an embryo a person?• Is it morally acceptable to use embryos for

research?• When do we become “human beings?”

People in the US affected by diseases that may be helped by stem cell research

Condition Number of Persons AffectedCardiovascular diseases 58 MillionAutoimmune diseases 30 MillionDiabetes 16 MillionOsteoporosis 10 MillionCancer 8.2 MillionAlzheimer's disease 4 MillionParkinson's disease 1.5 MillionBurns (severe) 0.3 MillionSpinal cord injuries 0.25 MillionBirth defects 150,000 (per year)Total 128.4 Million --------------------------------------------------------------------------------------Data from the Patients' Coalition for Urgent Research, Washington, DC (according

to Perry, Ref. 267).

How can scientists ensure ethical conduct in stem cell research

• Education for researchers– Routine emphasis by principle investigators– Emphasis by funding agencies– Classes and seminars

• Education for the public– Understand the importance of research– Understand that scientists are under ethical guidance

• Communication and open dialogue– Understand each others’ opinion– Reach a rationale common ground.

• Last step: Legal reinforcement

Useful Resources

• National Institute of Health resource for stem cells (http://stemcells.nih.gov)

• International Society for Stem Cell Research: “Guidelines for the Conduct of Human Embryonic Stem Cell Research (www.isscr.org)”

• National Academy of Science: “Guidelines for human embryonic stem cell research” (http://www.nap.edu/openbook.php?isbn=0309096537)