Stresses determine the shape of life
Sep 22, 2006
Patterns are everywhere in nature, from the leopard's spots to the nautilus's spiral shell, but scientists struggle to understand the mechanisms that produce them. Researchers in the US now believe that physics of microtubules is an important piece in the puzzle (Proc. Natl Acad. Sci. 103 10654).
Jim Valles and Jay Tang at Brown University, have worked out that physics is behind the patterns formed by microtubules – proteins that play a fundamental role in cell division and organism development. "What's exciting is that this finding may provide insight into how the shapes that make up the human body are created," said Valles.
Microtubules are shaped like long, thin straws and are found in all cells - whether that's the humble amoeba or a human brain cell. They perform many functions, including forming the structure that pulls the chromosomes apart during cell division and serving as the "train tracks" to transport proteins around cells. They also form the scaffolds that give cells their shape.
During the study, which was funded by NASA, the researchers investigated solutions of microtubules grown in the lab. The presence of a magnetic field or convective flow in the solution prompted the microtubules to align side by side and join to form a series of bundles. These bundles eventually buckled coherently with their neighbours to form a wave pattern.
"There is no direct evidence for how this pattern affects the formation of biological structures, but it suggests a mechanism for pattern formation – it could produce ripples in a cell or spatial variations in a protein," Valles told medicalphysicsweb.
The Tang-Valles team - with contributions from two graduate students, Yifeng Liu and Yongxing Guo - has spent two years studying this particular pattern, and finally it has the answer to how it forms. Rather than being solely generated by chemical reactions, as was previously suspected, the waves are produced by a combination of protein polymerization and mechanical buckling. "We suggest that the bundles buckle to relieve compressional stress that builds up because of internal MT [microtubule] polymerization forces," noted the researchers in their Proc. Natl Acad. Sci. paper.
The breakthrough will most likely increase basic understanding of several natural systems. Microtubule patterns similar to those created by the Tang-Valles team in the lab are seen in frog eggs and fruit-fly cells during early development, where they play a critical role in shaping the body of the organism that eventually emerges. Although the team didn't study any other patterns, there are a range of other possible structures that microtubules can form and physical forces are likely to underlie these as well.
Right now, it is impossible to say whether the Brown findings will have any medical implications. The pattern-formation mechanism is not genetically related, so it won't affect fields such as cloning, stem-cell research and reproductive medicine. "It could maybe affect tissue engineering as it is a force-generating mechanism – a distorting system," Valles speculated.
The team would now like to look more closely at the structure of the microtubule bundles. "We're interested in how easily they slide past each other. Our experiments have indicated that they are held together laterally but that they can move longitudinally," said Valles.
The researchers eventually want to be able to control the buckling effect. "Interest from groups in biology and medicine who could come up with applications for this work would also be very welcome," added Valles.
• This article originally appeared on medicalphysicsweb
About the author
Michelle Jeandron is science and technology reporter on medicalphysicsweb.