The Science and Ethics of
Stem Cell Research
Plenty of
Planaria
Laboratory Investigation
What are Planaria?
 Freshwater flatworms (phylum: Platyhelminthes)
 Live in freshwater under leaves and stones
 Avoid light (“negative phototaxis”)
 Free living – not parasites
 Carnivores – eat decaying meat, insects and larvae
(egg yolks or liver in the lab)
 1-20 mm in size
 Long lived
 Use sexual or asexual reproduction
This picture has been released it into the public domain.
Overview of Brown Planaria
Dugesia tigrina
Planaria are complex organisms
Gastrovascular
System
Nervous
System
Reproductive
System
Excretory/Osmoregulatory
System
Why study Planaria
to learn about stem cells?
 Planaria have an amazing ability to regenerate parts of
themselves
 Planaria regeneration is a great model for demonstrating
stem cell function and complexity of tissue regeneration
 They can grow easily in the lab
1/279th
Neoblast = Planaria Stem Cell
 20-30% of all the cells in a planaria are
Neoblasts.
 Neoblasts divide by mitosis and can
make more of themselves. They are the
only dividing cells in planaria.
 When a planaria is wounded, neoblasts
migrate to the site and begin dividing
Ann. Rev. Cell. Dev. Biol. 20:725-757, 2004
 Neoblasts can become ANY cell the
planaria needs—nerve cells, flame
cells, reproductive cells…
Three types of planaria
with their neoblasts
labeled with BrdU
BrdU (bromodeoxyuridine) is
substituted for thymine during DNA
replication. Only dividing cells—in this
case the neoblasts—will show
detectible amounts of BrdU.
(Dev. Biol 220: 142-153, 2000)
A. Phagocata sp.
B. Girardia dorotocephala
C. Schmidtea mediterranea
Dugesia sp.
Neoblasts and Stem Cells are Totipotent
“Totipotent” Stem Cell
Blood
Nerve
Skin
They can become any cell type in the body
In Humans: Totipotent cells are limited to
early embryonic division
In Planaria: Neoblasts are always present
Regeneration requires…
turning on the
right genes at the
right time
in the cells that come from the
dividing stem cells (neoblast).
Care and Feeding of Planaria

The water is very important! Fresh water from a
pond, stream or lake is best; spring water is adequate

Keep cultures in a cool, dark place

Feed planaria at least once a week

Change the water twice a week, especially after
feeding

After cutting them, the cultures should not be fed
Student Laboratory Investigation
Each team will receive 3 planaria:
 Experimental Planaria #1
Every team will cut this into half, separating
the anterior from the posterior halves.
 Experimental Planaria #2
This will be cut in a manner determined by your team.
 Control Planaria
This will not be cut.
Used with permission from UC Museum of Paleontology
Plenty of Planaria
Planaria Regeneration, Days 1 - 14
Slide courtesy of Dr. Sánchez Alvarado and Dr. Kyle Gurley
Slide courtesy of Dr. Sánchez Alvarado and Dr. Kyle Gurley
Slide courtesy of Dr. Sánchez Alvarado and Dr. Kyle Gurley
The Science and Ethics of
Stem Cell Research
Plenty of
Planaria
Laboratory Investigation