Plenty of Planaria

Laboratory Investigation

The Science and Ethics of Stem Cell Research

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

GastrovascularSystem

Nervous System

Reproductive System

Excretory/OsmoregulatorySystem

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

Plenty of Planaria

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 twice a week

Change the water after feeding

After cutting them, the cultures should not be fed