Wendy  Beane  Planaria

Planarian Flatworms

Planarians are non-parasitic members of the class Turbellaria (phylum Platyhelminthes).  There are thousands of species–they live in lakes and rivers, the ocean, and even on land (if the soil is moist enough).  We use freshwater species, largely for the ease of care…we keep them at room temperature, in the dark (as they are photophobic), in plain mineral water (think bottled water just like you probably drink), in tupperware containers:



We use mainly two species in the lab: Schmidtea mediterranea (on the left), which has a sequenced genome and for which there exist both an obligate asexual strain and a sexual strain (planarians are hermaphroditic); and Dugesia japonica (on the right), which are larger and hardier and perfectly suited to chemical genetic screens.


Planarians are a powerful regeneration model because they can reproduce asexually, by transverse fissioning.  During fissioning, worms basically attach themselves by their tail and then stretch until they pull themselves apart and separate into two pieces!!!  The head fragment will regenerate a new tail, and the tail fragment will regenerate a new head.  And 7-14 days later, you have two worms instead of just one…both genetically identical!  In the movie at the top of this page, you can see both a tail fragment and the head fragment from which it fissioned, both moving about (even though the tail fragment has not regenerated a brain yet!).   Planarians are able to do this remarkable feat because roughly 20% of their body is made up of adult stem cells, able to regenerate all tissues the worm may need to replace.

In the lab, we utilize this ability to further our understanding of regeneration:


It doesn’t matter how you cut them, planarians will regenerate!

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