Does exercise promote development? The sea anemone is all about how you move

As humans, we know that an active lifestyle gives us some control over our shape. Hitting the sidewalk, tracking our steps, and hitting the gym allows us to maintain muscle growth and reduce body fat. Our physical activity helps shape our physical figure. But what if we maintained similar aerobic exercise in our earlier forms? Is it possible that our embryos trained too?

Researchers from EMBL’s Ikmi group applied these questions to the sea anemone to understand how behavior affects body shape during early development. It turns out sea anemones also benefit from an active lifestyle, especially as they grow from egg-shaped swimming larvae to sedentary, tubular polyps. This morphological transformation is a fundamental transition in the life history of many cnidarian species, including the immortal jellyfish and the builders of our planet’s richest and most complex ecosystem, the coral reefs.

During development, starlet sea anemone larvae (Nematostella) perform a specific pattern of gymnastic movements. Too much or too little muscle activity, or a drastic change in the organization of their muscles, can cause sea anemones to deviate from their normal shape.

In a new article published in Current BiologyThe Ikmi group studies how this type of behavior affects the development of animals. With expertise in live imaging, computational methodology, biophysics and genetics, the multidisciplinary team of scientists turned live 2D and 3D imaging into quantitative features to track changes in the body. They found that developing sea anemones behave like hydraulic pumps, regulating body pressure through muscle activity and using hydraulics to shape the larval tissues.

“Humans use a skeleton of muscles and bones to move. In contrast, sea anemones use a hydroskeleton made up of muscles and a water-filled cavity,” said Aissam Ikmi, EMBL group leader. The same hydraulic muscles that help developing sea anemones move also appear to influence their development. Using an image analysis pipeline to measure body column length, diameter, estimated volume and motility in large datasets, scientists found that Nematostella larvae naturally divide into two groups: slow- and fast-developing larvae. To the team’s surprise, the more active the larvae are, the longer it takes for them to develop. “Our work shows how evolving sea anemones essentially ‘train’ to build their morphology, but it appears that they cannot use their hydroskeleton to move and evolve simultaneously,” Ikmi said.

Build microscopes and build balloons

“There were many challenges with this research,” explains first author and former EMBL predoctoral fellow Anniek Stokkermans, now a postdoctoral fellow at the Hubrecht Institute in the Netherlands. “This animal is very active. Most microscopes can’t record fast enough to keep up with the animal’s movements, resulting in blurry images, especially when looking at it in 3D. Also, the animal is quite dense, so most microscopes don’t even see halfway through the animal.”

To see both deeper and faster, Ling Wang, an applications engineer in the Prevedel group at EMBL, built a microscope to capture live, developing sea anemone larvae in 3D during their natural behavior.

“For this project, Ling specially adapted one of our core technologies, Optical Coherence Microscopy, or OCM. The main advantage of OCM is that it allows the animals to move freely under the microscope while still providing a clear, detailed view of the interior and in 3D,” said Robert Prevedel, EMBL group leader. “It was an exciting project showing the many different interfaces between EMBL groups and disciplines.”

Using this specialized tool, researchers were able to quantify volumetric changes in tissue and body cavity. “To increase their size, sea anemones inflate themselves like a balloon by absorbing water from the environment,” Stokkermans explained. “By contracting different muscle types, they can then regulate their short-term shape, much like squeezing an inflated balloon on one side and watching it expand on the other side. We believe that this pressure-driven local expansion helps stretch the tissue, so the animal slowly lengthens. In this way, contractions can have both short-term and long-term effects.”

balloons and sea anemones

In order to better understand the hydraulics and their function, the researchers worked together with experts from various disciplines. Prachiti Moghe, an EMBL predoctoral researcher in the Hiiragi group, measured changes in pressure that drive body deformations. In addition, Harvard University mathematician L. Mahadevan and engineer Aditi Chakrabarti presented a mathematical model to quantify the role of hydraulic pressure in controlling shape changes at the system level. They also constructed reinforced balloons with ribbons and ribbons that mimic the different shapes and sizes found in both normal and muscle-damaged animals.

“Given the ubiquity of hydrostatic skeletons in the animal kingdom, particularly in marine invertebrates, our study suggests that active muscle hydraulics play a broad role in the design principle of soft-bodied animals,” Ikmi said. “In many engineered systems, hydraulics are defined by the ability to harness pressure and flow into mechanical work, with far-reaching implications in spacetime. As animal multicellularity evolved in an aquatic environment, we propose that early animals likely exploited the same physics, with hydraulics driving both developmental and behavioral decisions.

As the Ikmi group has previously studied the links between diet and tentacle development, this research adds a new layer to understanding how body shapes develop.

“We still have many questions about these new findings. Why are there different activity levels? How exactly do cells sense pressure and translate it into a developmental outcome?” asked Stokkermans, pondering where this research is headed. “Since tube-like structures form the basis of many of our organs, studying the mechanisms applicable to Nematostella will also help gain a deeper understanding of how hydraulics play a role in organ development and function.”