The Growth of an Organism Rides on a Pattern of Waves

When an egg cell of virtually any kind of sexually reproducing species is fertilized, it triggers a chain of waves that ripple across the egg’s surface area. These waves are created by billions of activated proteins that rise through the egg’s membrane layer like streams of little delving sentinels, indicating the egg begins dividing, folding, and separating again to form the initial cellular seeds of an organism.

Now MIT researchers have taken a detailed view of the pattern of these waves generated on the surface of starfish eggs. These eggs are big and also, for that reason, easy to observe, and scientists regard starfish eggs as representative of the eggs of numerous other animal species.

In each egg, the group introduced a protein to emulate the onset of fertilization and recorded the pattern of waves that ripple throughout their surfaces in response. They observed that each wave arose in a spiral pattern and that multiple spirals whirled over an egg’s surface at a time. Some spirals automatically appeared and swirled away in opposite directions, while others collided head-on and instantly went away.

The researchers understood that the behavior of these swirling waves resembles the waves produced in other, apparently unrelated systems, such as the vortices in quantum liquids, the circulations in the atmosphere and oceans, and the electrical signals that travel through the heart and brain.

“Very little was learned about the dynamics of these surface waves in eggs, and after we started evaluating and modeling these waves, we discovered these very same patterns show up in all these other systems,” states physicist Nikta Fakhri, the Thomas D. and Virginia W. Cabot Assistant Professor at MIT. “It is an exhibition of this universal wave pattern.”

“It opens an entirely new point of view,” includes Jörn Dunkel, associate professor of mathematics at MIT. “You can adopt many techniques people have developed to examine similar patterns in various other systems, to discover something about biology.”

In the journal Nature Physics, Fakhri and Dunkel published their results on March 7. Their co-authors are Tzer Han Tan, Jinghui Liu, Pearson Miller, and Melis Tekant of MIT.

Finding one’s center

Earlier research has revealed that fertilizing an egg activates Rho-GTP immediately, a protein inside the egg that drifts typically around the cell’s cytoplasm in an inactive state. When activated, billions of proteins rise out of the cytoplasm’s morass to affix to the egg’s membrane layer, twisting along the wall in waves.

“Visualize if you have an unclean aquarium, and when a fish swims near the glass, you can see it,” Dunkel discusses. “Similarly, the proteins are somewhere inside the cell, as well as when they become activated, they affix to the membrane, and you begin to see them move.”

Fakhri says the waves of proteins crossing the egg’s membrane serve, partly, to organize cell division around the cell’s core.

“The egg is a large cell, and these proteins have to collaborate to find its center, to ensure that the cell knows where to split and fold up, many times over, to form an organism,” Fakhri claims. “Without these proteins making waves, the cellular division would not occur.”

Their research focused on the active type of Rho-GTP and the pattern of waves generated on an egg’s surface area when they changed the protein’s concentration.

For their experiments, they obtained approximately ten eggs from the ovaries of starfish with minimally invasive surgery. They administered a hormone to spur maturation and infused fluorescent markers to attach to any active type of Rho-GTP that rose in response. They then observed each egg via a confocal microscopic lens. They watched as billions of proteins activated and rippled throughout the egg’s surface in response to differing concentrations of the artificial hormone protein.

“In this way, we developed a kaleidoscope of different patterns and observed their resulting characteristics,” Fakhri says.

Hurricane track

The scientists first put together black-and-white videos of each egg, showing the bright waves traversed its surface. The brighter a region in a wave, the higher the concentration of Rho-GTP in that specific region. For each video clip, they compared the brightness or concentration of protein from pixel to pixel and utilized these comparisons to produce an animation of the same wave patterns.

The group observed that waves appeared to oscillate outward as tiny, hurricane-like spirals from their video. The scientists traced the origin of each wave to the core of each spiral, which they refer to as a “topological defect.” Out of curiosity, they followed the movement of these defects themselves. They did some statistical evaluation to establish precisely how fast specific defects crossed an egg’s surface area, as well as how frequently and in what configurations the spirals turned up, collided, and vanished.

In an unexpected twist, they found that their statistical outcomes and the behavior of waves on an egg’s surface were equal to the behavior of waves in other bigger and relatively unrelated systems.

“When you see the statistics of these issues, it is basically like the same vortices in a fluid, or waves on the brain or systems on a larger scale,” Dunkel says. “It is the same universal phenomenon, just scaled down to the level of a cell.”

Scientists are especially interested in the waves’ resemblance to concepts in quantum computing. Much like the pattern of waves in an egg conveys specific signals, in this situation of cell division, the quantum computer is a field that intends to manipulate atoms in a fluid in precise patterns to convert information and perform calculations.

“Maybe now we can borrow ideas from quantum fluids to develop minicomputers from biological cells,” Fakhri claims. “We expect some distinctions, but we will certainly attempt to explore [biologic signaling waves] even more as a tool for computation.”

This study was supported, in part, by the James S. McDonnell Structure, the Alfred P. Sloan Foundation, and the National Science Foundation.

Originally published on MIT NEWS. Read the original article.