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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.
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
Neoblasts = Planaria Stem Cell
(Dev. Biol 220: 142-153, 2000)
20-30% of all the cells in a planaria are Neoblasts.
They are present throughout the planaria (except far anterior & pharynx)
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
Neoblasts can become ANY cell the planaria needs—nerve cells, flame cells, reproductive cells…
Ann. Rev. Cell. Dev. Biol. 20:725-757, 2004
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
turning on the right genes at the right time in the cells that come from the
dividing stem cells (neoblast).
Regeneration requires…
Student Laboratory Investigation
Each team will receive 3 planaria:
Experimental Planaria #1Every team will cut this into half, separating
the anterior from the posterior halves.
Experimental Planaria #2This will be cut in a manner determined by your team.
Control PlanariaThis will not be cut.
Used with permission from UC Museum of Paleontology