Why Cant We Grow New Arms

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Summer 2007 Workshop in Biology and Multimedia
for High School Teachers
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Why Cant We Grow New Arms?

• An Introduction to Stem Cells and Regeneration

Image by mila zinkova from commons.wikimedia.org
http//en.wikipedia.org/wiki/ImageSea_star_regene
rating_legs.jpg, image by Mila Zankova
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• Greek myth says that zeus had prometheus chained
  to a rock for bringing fire to humans. Every day
  an eagle would come and eat his liver. By the
  time the eagle came back the next day, the liver
  had grown back.

Your liver can regenerate too! Will There be a
day When your arm or leg will grow back?
http//commons.wikimedia.org/wiki/ImageKoeln_wrm_
1044.jpg
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You have probably heard that sea stars can grow a
new arm if they lose one, or even that a lost arm
can grow into a whole new sea star.
Did you know that salamanders can also regenerate
lost limbs? This probably makes you wonder
Why cant we grow new arms?
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In order to answer that question, You will need
to understand a little bit about how the
salamander is able to regrow an arm and how your
arm is formed in the first place.
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Lesson Outline

• What are stem cells and where do they come from?
• How does a salamander regenerate a lost arm?
• Why cant we grow a new arm?
• What do stem cells have to do with limb
  development and regeneration?
• Can stem cells be used to grow new limbs?

These are the questions you should be able to
answer by the end of this lesson. As you proceed
through the lesson, click on the green links to
answer the questions on your worksheet. As you
scroll over the links, some of them have
instructions as to where on the page you should
look for the answers.
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I. What are stem cells and where do they come
from?

• You have undoubtedly heard of stem cells. They
  are in the news all the time, but what exactly is
  a stem cell?

http//commons.wikimedia.org/wiki/ImageMouse_embr
yonic_stem_cells.jpg
Mouse embryonic stem cells
Learn about stem cells
Answer question 1
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I. What are stem cells and where do they come
from?

• B. There are two types of stem cells, embryonic
  and adult. Find out how both are isolated, some
  similarities, and some differences.

http//commons.wikimedia.org/wiki/ImageStem_cells
_diagram.png
Pluripotent, embryonic stem cells originate as
inner mass cells with in a blastocyst. The stem
cells can become any tissue in the body,
excluding a placenta. Only the morula's cells are
totipotent, able to become all tissues and a
placenta.
Embryonic vs. Adult Stem Cells
Where the cells are found
Answer question 2
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II. How Does a salamander Regenerate a Lost Arm?

• Imagine if humans could grow new limbs after
  amputation. Some salamanders can do just that.

Photograph taken by Patrick Coin
http//commons.wikimedia.org/wiki/ImagePlethodon_
cylindraceusPCCA20060409-3183A.jpg
Read about limb regeneration in salamanders
Visual of limb regeneration in salamander
Limb Regeneration Movie
Answer questions 3-6
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II. How Does a salamander Regenerate a Lost Arm?

• Review the basic steps of limb regeneration
• An epidermal layer covers the wound.
• Cells in the stump become unspecialized and
  accumulate under the epidermis. This structuure
  is the blastema.
• The blastema elongates and flattens while cells
  are differentiating.
• Finally new bones form and the limb pattern is
  back to normal.
• The new limb grows and looks just like a normal
  limb.

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III. Why Cant We Grow a New Arm?

• First take a look at how a vertebrate limb
  develops in the first place.

Vertebrate Limb Development
Answer questions 7-9
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III. Why Cant We Grow a New Arm?

• As you can see, creating an arm is a very complex
  process that requires a number of different
  genes. Each step can trigger the next, and more
  and more genes and environmental factors get
  involved.

http//commons.wikimedia.org/wiki/ImageLimb_bud.p
ngorg by Peter Znamenski
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III. Why Cant We Grow a New Arm?

• It is still unclear why salamanders can
  regenerate limbs while mammals and other
  vertebrates cannot.
• It may have something to do with the complexity,
  but there is more to it than that.

Why do we form a scar instead of a new limb?
Answer question 10
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IV. What do stem cells have to do with limb
development and regeneration?

• Now that you know what stem cells are, how a limb
  develops and how a salamanders limb can
  regenerate, you may be wondering
• What do stem cells have to do with limb
  development and regeneration?

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IV. What do stem cells have to do with limb
development and regeneration?

• Remember that stem cells are cells that can
  self-renew and make cells that can differentiate.

This image shows how a hematopoietic stem cell
(an adult blood stem cell) can differentiate into
all of the different types of blood cells.
http//stemcells.nih.gov/info/basics/basiImage
courtesy of HINcs4.asp
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IV. What do stem cells have to do with limb
development and regeneration?

• In order for limbs (or any other body part) to
  develop, the stem cells must receive the proper
  signals. Each organ requires different signals
  or a different order of signals. So, during
  development, stem cells for blood will receive
  different information than those for skin or
  neurons.

To get a better Idea of this concept play the
virtual stem cell laboratory from childrens
Hospital boston
Answer questions 11-12
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IV. What do stem cells have to do with limb
development and regeneration?

• In salamander limb regeneration, it is unclear
  whether stem cells are involved, but it is known
  that there are some in the tissue that may
  contribute.
• We know that when a human muscle is damaged stem
  cells are responsible for repair.

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IV. What do stem cells have to do with limb
development and regeneration?

• Put together all of the information you now have
  about stem cells, development, and regeneration
  to figure out what scientists might want to
  research in order to promote limb growth in
  humans.
• Answer question 13.

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This leads us to our final question
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V. Can Stem Cells Be Used to Grow a New Arm?
Image by emo_boy from http//www.abstractinfluenc
e.com/forums/album_pic.php?pic_id8414

• Many scientists are working on this problem right
  now. They are studying frogs, salamanders, sea
  stars, and even mice to figure out how they can
  regenerate limbs or other body parts.

Photo CreditUS National Oceanic and Atmospheric
Administration
http//upload.wikimedia.org/wikipedia/commons/b/b1
/Reef0296.jpg
Image from http//commons.wikimedia.org/wiki/Image
Mus_Musculus-huismuis.jpgfilecommons.wikimedia.
org
http//commons.wikimedia.org/wiki/ImageSpiral_Sal
amander.jpgfile
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Now find an article about studies into limb
regeneration.

• Read the Article and write down the source.
  Then, summarize the article and hand it in with
  your Stem Cells and Regeneration worksheet.

end
Extension, Learn More, References
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extension
Use some of the links below to answer question I.
Then, write about your own opinions. Be sure to
explain how you feel and give reasons for your
opinion.

• Why are some people opposed to stem cell
  research?
• How do I feel about stem cell research and use?

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Learn More

• If you would like more information on stem cells,
  regeneration or development, go back to any of
  the links in this presentation or check out some
  of the following
• The book Mutants by Armand Marie Leroi discusses
  human development through mutation. It is full
  of interesting stories and science.
• http//www.unews.utah.edu/p/?r050306-6 - article
  about research grant at University of Utah
• http//www.regen.iupui.edu/research_appendage.asp
  - information about research on limb regeneration
  at Indiana University
• http//discoverysedge.mayo.edu/regenerative_biolog
  y/index.cfm - online research magazine from the
  mayo clinic
• http//www.mirm.pitt.edu/ - McGowan Institute for
  Regenerative Medicine From University of
  Pittsburgh
• http//www.isscr.org/public/selected_topics.htm -
  International Society for Stem Cells
• http//stemcell.stanford.edu/101/ - Stanford
  Institute for Stem Cell biology and Regenerative
  Medicine
• http//www.hsci.harvard.edu/ - Harvard Stem Cell
  Institute

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References

• Amphibian Limb Regeneration http//www.uoguelph.ca
  /zoology/devobio/210labs/regen1.html
• Commons.wikimedia.org
• Morrison, Jamie L. et al Salamander limb
  regeneration involves the activation of a
  multipotent skeletal muscle satellite cell
  population JCB 30 January 2006
  http//www.jcb.org/cgi/content/full/172/3/433
• Salamanders Re-grow Lost Limbs, Could Human
  Medicine Benefit From Understanding Regeneration?
  Science Daily 1 April 2007 http//www.sciencedaily
  .com/releases/2007/03/070330111307.htm
• Stem Cell Basics What are adult stem cells? . In
  Stem Cell Information World Wide Web site.
  Bethesda, MD National Institutes of Health, U.S.
  Department of Health and Human Services, 2006
  cited Wednesday, July 18, 2007 Available at
  http//stemcells.nih.gov/info/basics/basics4
• Stocum, David L. Biology and Medicine An
  Overview 1 July 2004 http//www.cellscience.com/Re
  views1/Regenerative_Biology_and_Medicine.html
• Vertebrate Limb Development--an Example of the
  Development of Body Parts http//www.indiana.edu/
  oso/evolution/limbs.htm