From worm to man

Our bodies are perfectly capable of renewing billions of cells every day but fail miserably when it comes to replacing damaged organs such as kidneys. Using the flatworm Schmidtea mediterranea—famous for its capacity to regrow complete animals from minuscule flecks of tissue—as an eloquent example, research conducted in the laboratory of Howard Hughes Medical Institute Investigator Alejandro Sanchéz Alvarado, PhD, revealed how our distant evolutionary cousins regenerate their excretory systems from scratch.

Planarian protonephridia, which are distributed throughout a flatworm’s body, combine pressure filtration with filtrate modification similar to mammalian nephrons, the basic functional unit of kidneys. To study protonephridias’ development the researchers simply cut the animals’ heads off and watched how they regrew the missing body part including excretory tubules within a week. They found that protonephridial tubules originated from a precursor structure, which undergoes extensive branching morphogenesis, the same process that also shapes vertebrate organs such as lung, kidneys or mammary glands.

“We take it for granted that we go to bed with two sets of fully functional kidneys and that we wake up with them the next morning but we don’t understand the fundamental processes that give rise to this very well choreographed maintenance of an organism’s form and function,” says Sanchéz Alvarado. “We can now start to use planaria as a model to begin to understand how an adult animal maintain their form and function over a very long time.”

Their study was published in the August 2011 issue of the journal Development.