A microscopic worm may shed light on how we perceive gravity

While humans rely on gravity for balance and orientation, the mechanisms by which we actually sense this fundamental force are largely unknown. Odder still, the model organism C. elegans, a microscopic worm, can also sense the direction of gravity, even though there is no known ecological reason for it to do so.

Micrsoscopic view of Caenorhabditis elegans, a free-living transparent nematode, about 1 mm in length
Caenorhabditis elegans, a free-living transparent roundworm, about 1 mm in length.

To untangle this mystery and get at the fundamentals of our own sense of gravity, a team of Penn Engineering researchers led by Haim Bau, professor in mechanical engineering and applied mechanics, and David Raizen, associate professor in neurology at the Perelman School of Medicine, conducted a series of experiments on this model organism. The lead author, Alex Chen, a then-visiting doctoral student, and co-authors, Hungtang Ko, a then-master’s student, and Oswald Chuang, a former postdoctoral fellow, contributed to this work while working in both Bau’s and Raizen’s labs.

Even with its extremely simple physiology, C. elegans shares more than half of its genes with humans, allowing genetic studies to give insight into which genes are responsible for similar traits in humans.

“We were working in previous research on hydrodynamics of C. elegans, dropping them into water, when we observed that these worms all tended to swim towards the bottom of the cuvette,” says Bau. “We wondered if they were responding to gravity or just top-heavy and passively sinking.”

Recognizing this as an opportunity to pinpoint molecular pathways responsible for gravitaxis, or the ability to move in response to gravitational forces, the team initiated the study, which is published in the journal BMC Biology.

“We know dopamine is a very common neurotransmitter that controls many functions in the body. When we turned it off in mutants, the ability to detect gravity was lost,” says Bau.

“Interestingly, when worms were exposed to dopamine supplements at the larval development stage and later, in the solution, some of that ability came back, indicating that pharmaceutical recovery may be possible,” he says.

This connection between dopamine and gravity sensing provides insight into applications for human health.

This story is by Melissa Pappas. Read more at Penn Engineering Today.