Biologists unravel the tangled mystery of cell growth

When cells do not divide into adequate copies of themselves, living things do not grow as they should. For the first time, scientists now understand how a protein called TANGLED1 can lead to precise cell division in plants.

Inside cells are structures called microtubules, which act as roads to move proteins and organelles. They are also critical for separating DNA after it has duplicated to eventually form two cells into one.

“You can’t live without microtubules, and plants can’t,” said Carolyn Rasmussen, an assistant professor of plant cell biology at UC Riveride. “Because they are so important, you have to carefully monitor where they go and how they move.”

Rasmussen and colleagues discovered that the TANGLED1 protein performs this microtubule control function by attaching the microtubules together as glue. His description of how TANGLED1 works was published today in the Cell Biology Magazine.

By adding microtubules and TANGLED1 together in a test tube, the team saw surprising interactions between them. Often, proteins can only group microtubules at very specific angles: 40 degrees or less. TANGLED1 can grab microtubules from any angle and bind them together.

“As far as I know, this is the first plant protein observed in vitro with this characteristic,” said Rasmussen.

The protein’s ability to capture and stabilize microtubules is probably critical in order to adequately separate daughter cells. Cell divisions at the wrong angle lead to big problems, such as tumor formation.

Animal cells normally need to remain attached to a surface, and their division is controlled to ensure that the cells remain there. If a cell decouples from the surface after division, that could mark the beginning of a tumor.

Rasmussen’s team included Pablo Martinez, Sean O’Leary and Antonia Zhang of UC Riverside; biochemists Ram Dixit and Rachappa Balkunde from the University of Washington; and mathematician Kenneth Brakke of Susquehanna University.

Now that the team has seen TANGLED1 working in vitro, the next step is to observe it in a living cell. If they can gain a deeper understanding of the genes that control plant cell division, these genes could be manipulated to produce higher-yielding crops, such as larger ears of corn or more grain.

An additional benefit of this research is the insight that it could bring to human cellular processes. When there are defects in the cell’s ability to move the material in the microtubules, diseases such as Alzheimer’s disease or cancer could follow.

Research on these diseases is often done in human cell lines or animal models. However, there are similarities between the microtubule clustering behavior of TANGLED1 in plants and the microtubule binding proteins in humans, making it easier to learn more by characterizing both at the same time.

“People say that plants don’t get cancer, which is generally true,” said Rasmussen. “But sometimes, when you have a different perspective on a related question, in this case, what controls the spatial positioning of cell division, you can see things that are difficult to see in other model systems.”