Research conducted by assistant professor of physics Dimitrios Vavylonis
explaining key processes in cell division was accepted into publication in Science
in a paper entitled “Assembly mechanism of the contractile ring for cytokinesis by fission yeast.” Vavylonis is co-first author of the paper, which appeared online as a Science Express
article on December 13.
The paper is the culmination of extensive research conducted by a highly interdisciplinary team of physicists including Vavylonis and Ben O’Shaughnessy and biologists Jian-Qui Wu, Steven Hao and Thomas D. Pollard, representing Lehigh, Yale and Columbia Universities.
During the cell cycle, mitosis occurs, splitting the cell into two daughter cells. Cytokinesis is the last step of mitosis, and concludes the cell cycle. Scientists have addressed some of the major questions regarding cytokinesis such as: How do cells actually divide themselves into two? What kind of structure or “machine” does the cell assemble to achieve this? And, how is this assembly achieved?
It is known that this “machine” is actually a contractile ring which is assembled in the cell and then pinches the cell into two parts by shrinking down, much like a purse-string. Vavylonis’s research focused on the assembly of that contractile ring.
“Our paper is important because it provides the first concrete mechanistic explanation for the assembly of the contractile ring,” says Vavylonis, whose team describes their work as an exciting and modern approach to unlocking the mysteries of life.
The team used fluorescent proteins originally extracted genetically from fluorescent jellyfish in the 1990s to light up components of the contractile ring within live dividing cells. The team determined that fission yeast cells assemble the contractile ring in a mechanism they called “search, capture, pull and release.”
“This is a mechanism reminiscent of trial and error,” said Vavylonis. “Pairs of protein nodes formed during mitosis get randomly connected to one other, attract and then release. The releasing of these connections initiates subsequent rounds of search and capture, and appears to be an essential part of the assembly process.” Nodes are eventually positioned into a condensed contractile ring around the equator, ready to pinch the mother into two daughters at a later stage.
A novel aspect of the team’s work was the use of computer simulations at every step to test what is feasible physically and to help guide experiments. The simulations indicated that cells use reaction rates that are nearly ideal to make this search, capture, pull and release mechanism work on the time scale of the events in the cells.
Vavylonis, who joined the department of physics
in 2006, began this research during his postdoctoral research at Columbia and Yale Universities. His work at Lehigh has provided essential contributions to the research, which will now shift to examining additional mechanisms.