New Study Deepens Our Understanding of How Animals Learned to Move

In the above image, hydra’s neurons are labeled with a green fluorescence indicator. (Yuste Lab, Columbia University)

For the first time, Columbia researchers have captured images and measured the activity of every muscle in a living animal, offering a fresh perspective on the fundamental principles of neuromuscular function in the animal kingdom as well as insight into the story of evolution.

Their study, published today in Current Biology, maps the musculature of Hydra, a freshwater polyp with a hollow tube of a body consisting of just two layers of muscle. The researchers used a calcium-imaging technique developed at Columbia to image the “firing” activity of the Hydra’s muscle cells. Surprisingly, they found that individual cells are not dedicated to particular muscular patterns but rather participate in multiple emergent patterns that move through the Hydra’s muscle.

“Our research helps us understand the evolution of neuromuscular systems – the story of how animals learned to move,” said John Szymanski, the lead author of the paper.

“The Hydra is part of an animal group that took a divergent evolutionary path than most animals millions of years ago and our study sheds some light on how an ancient animal may have first developed coordinated motion, added Szymanski, who did the study as a neuro-biological researcher in Columbia’s Rafael Yuste’s Laboratory. “Hydra helps us tell the story of how the neuromuscular system evolved to give all animals, including humans, the ability to move.”

All animals have a common ancestor, and the last common ancestor between Hydras and humans existed 750 million years ago, near the earliest stage of animal evolution. Studying the Hydra’s musculature thus offer a unique insight into the fundamental principles of neuromuscular function that are common to all animals, Szymanski said.

Hydras, freshwater relatives of jellyfish, corals, and sea anemones, are 1-10 millimeters long. They are found in freshwater habitats such as lakes, ponds, and slow-flowing rivers. They belong to the phylum Cnidaria, which are characterized by tube-like radial bodies and stinging tentacles. Their body is a hollow tube consisting of two layers of muscle cells, an inner endoderm layer and an outer layer of ectoderm cells. The simple anatomy of two sheaths of muscle make the Hydra a good specimen for biological observation.

Rafael Yuste, director of the Yuste Lab, helped develop the calcium-imaging technique the researchers used to image the Hydra’s muscles cells, having earlier used it to study neuronal circuits. Here, the researchers adapted the technique to study the Hydra’s neuromuscular system. The technique allowed them to visualize the changes in calcium that accompany electrical activity and contraction in the Hydra’s muscle cells. Muscles are excitable cells that “fire” and calcium is the key signaling molecule that affects a muscular contraction, which allows animals to move, explains Yuste.

The Hydra is part of a group of animals that branched off other animals very early in evolution, “giving us a peek into what may have happened 750 million years ago in evolution,” said Yuste. Although Hydra has a simple structure, its muscles cells serve many functions. “So muscles probably evolved as swiss-army knives types of cells, and then became very specialized in the bilaterian and vertebrate lineages,” he said.

The multi-functionality of its cells allows the Hydra to perform a variety of movements with a simple body plan that contains only a few cells—presumably, anatomy it has in common with the earliest metazoans, said Yuste, who is a member of Columbia’s Data Science Institute.

“Our findings suggest that in the earliest animals, multifunctional muscle tissues may have had a great deal of autonomy in processing information and generating their patterns of excitation,” added Yuste. “This research thus provides a unique perspective on fundamental principles of neuromuscular function in the animal kingdom and insight into the fascinating the story of their evolution.”

The research was supported by the National Science Foundation, the U.S. Army Research Laboratory and the U.S. Army Research Office. The researchers also spent three summers at the Marine Biological Laboratory (MBL) in Woods Hole, Mass., work that was supported by the H. Keffer Hartline, Edward F. MacNichol, Jr. Fellowship Fund, the E. E. Just Endowed Research Fellowship Fund, the Lucy B. Lemann Fellowship Fund, and the Frank R. Lillie Fellowship Fund.

— Robert Florida, Data Science Institute