Microtubules, assemble: New research may lead to better understanding of self-organization in cells

January 28, 2016
The microtubules organize into networks that spontaneously contract. Credit: Needleman Lab/HarvardSEAS

What bones are to bodies, the cytoskeleton is to cells. The cytoskeleton maintains cellular structure, builds appendages like flagella and, together with motor proteins, powers cellular movement, transport, and division. Microtubules are a critical component of the cytoskeleton, vital for cell division and, because of that, an excellent target for chemotherapy drugs.

Microtubules can spontaneously self-organize, transforming from many singular components into one large capable of performing specific tasks. Think Transformers. How they do that, however, has remained unclear.

Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have observed how microtubules and assemble into macroscopic networks. Their observation provides a better understanding of cytoskeletal self-organization in general, which may in turn lead to better drug design and new materials that can mimic cellular behaviors.

The research was recently published in the journal eLife.

Spindles are cellular structures that play an important role in , separating chromosomes and pulling the duplicated DNA from the mother cell into the daughter cell. They are made up of microtubules and many other proteins, including the motor protein dynein.

"What we are really looking for is a of spindle assembly," said Peter Foster, a graduate student at SEAS and the paper's first author. "We know how motor proteins interact with microtubules but how do you go from individual microtubules and motor proteins to large networked structures?"

Asters form as motor protein draws the minus ends of the purple microtubules together. Credit: Needleman Lab/Harvard SEAS

To gain insight into how spindles assemble, Foster and his team, under the leadership of Dan Needleman, associate professor of applied physics and of molecular and cellular biology, built a simple experiment. They extracted cytoplasm from frog eggs, which contains dynein and all of the components needed to make spindles, added fluorescent protein and the chemotherapy drug Taxol to create and stabilize microtubules, and loaded the mixture into "the world's simplest microfluidic chamber."

"Very quickly, we saw that these microtubules organize into networks that spontaneously contract," Foster said. "The question is why?"

The answer lay not in the microtubules but in the behavior of the motor protein. Microtubules have plus and minus ends and researchers have observed dynein moving from the plus end to the minus. As a result, the motor protein draws the minus ends of microtubules together, creating star-like clusters called asters. The dynein drives these small clusters together, fusing them to create larger and larger networks. As the motor protein continues to jam the together, the network contracts, until it can't get any smaller.

Based on this experiment, the researchers developed a model that quantifies and describes this behavior and lends insight into not only spindle assembly but also self-organization in general. This model could provide insights into how to design materials that can self-assemble or autonomously contract, like a self-squeezing sponge.

"Using this model, we can ask questions from the microscopic level all the way to large scale phenomena," Foster said. "There are many ramifications not only in biology but also in the material world."

Explore further: Molecular motor grows cell's microtubules

Related Stories

Molecular motor grows cell's microtubules

October 26, 2015

Motor proteins that pause at the ends of microtubules and produce pushing forces can also stimulate their growth, according to researchers at Penn State. The proteins' function could be a critical component in understanding ...

Friction harnessed by proteins helps organize cell division

April 16, 2014

(Phys.org) —A football-shaped structure, known as the mitotic spindle, makes cell division possible for many living things. This piece of cellular architecture, responsible for dividing up genetic material, is in constant ...

Molecular machine, not assembly line, assembles microtubules

August 20, 2015

When they think about how cells put together the molecules that make life work, biologists have tended to think of assembly lines: Add A to B, tack on C, and so on. But the reality might be more like a molecular version of ...

Recommended for you

The astonishing efficiency of life

November 17, 2017

All life on earth performs computations – and all computations require energy. From single-celled amoeba to multicellular organisms like humans, one of the most basic biological computations common across life is translation: ...

Unexpected finding solves 40-year old cytoskeleton mystery

November 17, 2017

Scientists have been searching for it for decades: the enzyme that cuts the amino acid tyrosine off an important part of the cell's skeleton. Researchers of the Netherlands Cancer Institute have now identified this mystery ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.