How do cells acquire their shapes? A new mechanism identified

Working with light to activate processes within genetically modified fission yeast cells is part of the research carried out by experimental biologists from the Martin Lab at the University of Lausanne, led by teacher Sophie Martin. The team members were conducting such experiments when they noticed that a certain protein, when introduced into the cell, would be displaced from the cell growth region. So they contacted Dimitrios Vavylonis, who heads the Vavylonis group at Lehigh University’s physics department, to find out why.

“We did a computer simulation that coupled the ‘growth’ of the cell membrane to the movement of proteins, as well as model a few other hypotheses that we considered after discussions with them,” says Vavylonis, a theoretical physicist.

This multidisciplinary collaboration combined modeling and experimentation to describe a previously unknown biological process. The teams discovered and characterized a new mechanism that a single yeast cell uses to acquire its shape. They describe these results in an article titled “Cell patterning by secretion-induced plasma membrane flow” in the latest issue of Scientists progress .

As cells move or grow, they have to add a new membrane to these growth regions, says Vavylonis. The process of membrane administration is called exocytosis. Cells must also deliver this membrane to a specific location in order to maintain a sense of direction, called “polarization,” or to grow in a coordinated fashion.

“We have shown that these processes are coupled: a local excess of exocytosis causes the removal (‘flux’) of some of the proteins attached to the membrane from the growth region,” explains Vavylonis. “These moving away proteins mark the cell region that is not growing, thus establishing a self-sustaining pattern, which gives rise to the tubular form of these yeast cells.”

This is the first time that this cellular structuring mechanism, the process by which cells acquire spatial non-uniformities on their surface, has been identified.

The simulations of the Vavylonis team, led by postdoctoral associate David Rutkowski, led to experimental tests that the Martin group then performed. Vavylonis and Rutkowski analyzed the results of the experiments to confirm that the distribution of the proteins they noticed in their simulations matched the data gleaned from the living cell experiments.

The team says the work may be of particular interest to researchers studying processes related to cell growth and membrane trafficking, such as neurobiologists and those who study cancer cell processes.

“Our work shows that models in biological systems are generally not static,” says Rutkowski. “Models are established through physical processes involving continuous flow and renewal.”

“We were able to provide support for the membrane flow structuring model,” said Vavylonis. “Ultimately, the Martin Group was able to use this knowledge to design cells whose shape can be controlled by light.”