Researchers Discover Mechanism of Cell Growth Control
In a groundbreaking study published in Science, biologists at the University of Miami Miller School of Medicine provide a novel perspective to important and fundamental questions in basic cell biology: How do cells control their growth and define their shape?
Led by senior author Fulvia Verde, Ph.D., associate professor of molecular and cellular pharmacology and cell biology, UM researchers discovered that the activity of Cdc42, a key protein that regulates cell morphology, displays “pulsing” dynamics, moving from one end to the other in fission yeast cells. The oscillation of Cdc42 appears to be a critical factor in expanding and shaping the yeast cells, a finding that sheds new light on the molecular mechanisms that control and change cell shape.
In the study, published online May 17 and titled, “Oscillatory Dynamics of Cdc42 GTPase in the Control of Polarized Growth,” researchers analyzed Cdc42 activity in growing cells by marking the proteins with fluorescence and documenting their activity through time-lapse microscopy. By recording changes in the level of the fluorescent markers at the cell tips, the researchers noticed that Cdc42 activity alternates between the two ends of the cell approximately every five minutes.
As Verde explained, this oscillatory behavior provides cells with the ability to change the direction of growth and adapt their form to respond to a fast-changing cellular environment. This exploratory behavior is a general strategy among all self-organizing biological systems, not just simple yeast, and, therefore, these findings could play a role in the development of drugs to control cell migration, or to promote neuronal growth.
“It was so exciting to discover this unexpected dynamic nature of Cdc42 activation in the cell,” said Maitreyi Das, Ph.D., assistant scientist in the Department of Molecular and Cellular Pharmacology and first author of the study. “This discovery opens the door to truly understanding the very complex and intricate mechanism of Cdc42 regulation as cells grow.”
The findings also underscore the power of combining rapid image-capture microscopy, genetic manipulation, and mathematical modeling. “We used a Systems Biology approach to describe the complex behavior of an important signaling molecule on a cell-wide level,” said Verde, citing the collaboration with Dimitrios Vavylonis, Ph.D., assistant professor of physics, and Tyler Drake, Ph.D. candidate, from Lehigh University.
In addition to discovering the oscillating activity of Cdc42, the Miller School team, which also included David J. Wiley, Ph.D., assistant scientist, and Peter Buchwald, Ph.D., assistant professor of molecular and cellular pharmacology, performed the microscopic observations and designed the genetic mutagenesis for the study.
The Lehigh team analyzed the data collected by the UM team and developed a mathematical model for the oscillatory behavior. This model predicted that changes in abundance or activity of Cdc42, or of its regulators, could alter specific aspects of cell growth by affecting Cdc42 dynamics.
For the past several years, Verde’s research has focused on understanding cell shape and growth control, particularly signaling pathways that regulate the dynamics of the cytoskeleton, and their role in the establishment of cell shape. Her lab uses a combination of techniques such as microscopy, yeast genetics, and cellular and molecular biology.
The study was funded by the National Science Foundation, the National Institutes of Health, a University of Miami SEEDS “You Choose” Leadership award, and a Graduate Assistance in Areas of National Need Fellowship through the U.S. Department of Education.