One long-standing mystery in biology is how the Hydra vulgaris - the tiny, multi-tentacled freshwater animal with a distant relation to the sea anemone - feeds. Now, a team of University of California, San Diego researchers may have answered this question using simple physics.
"The reason why this work is exciting is that there are very few systems in which you can do quantitative measurements in vivo," said Eva-Maria Collins, who headed the research team. "Hydra is such a simple organism; it allows us to perform controlled perturbations and quantitative measurements in the natural context."
The hydra is unique not only for its ability to regenerate its body when ripped apart but also for the fact that each time it opens its mouth, it tears a hole in its epithelial tissue. Until now, scientists were not certain how this feat was achieved at the cellular level due to their inability to see it.
Using transgenic hydras, the team was able to observe the process of the creature opening its mouth fully at fairly fast timescales - on the order of 60 seconds.
"It's fascinating that hydra has to tear a hole every time it opens its mouth," said Collins. "And that this process happens so quick; this was the first indication to us that mouth opening did not involve cellular rearrangements."
The team tagged the epithelial cells within the transgenic hydras and monitored their changes in position, revealing that no cellular rearrangement occurred when the hydra opened its mouth. Instead, they found that the mouth opening was achieved by impressive elastic deformations of the cells that surround it.
These elastic deformations are driven by radially oriented contractile elements called "myonemes," which are located in the hydra's ectodermal cells are act like muscles. Furthermore, they found that the degree to which the mouth is scaled open by these myonemes is likely controlled by nerve signaling.
The results can now be used to help researchers use similar techniques in order to examine organism development from an unstructured group of cells into a fully grown creature.
"We can now use this system to examine more closely two processes that are fundamental to all organisms: tissue formation and patterning," she said.
The findings were published in the March 8 issue of the Biophysical Journal.
