Amrinder Nain is an associate professor in the Department of Mechanical Engineering, but he doesn’t build cars or robots. The mechanisms it defends are the tiny building blocks of life and how they behave and move.
Cellular dynamics research studies living cells and their life, death, division and multiplication. Over the past few years, Nain has made many trips down the microscopic roads where cells live. His previous work has analyzed how cells move and has even included projects with colleagues to measure cellular forces and nucleus shapes and to electrify cells and observe how they heal.
A divided cell is how we stand
His latest collaboration studies how cells divide, particularly in the fibrous environment of living tissue. Cells are typically studied in a flat environment, and the difference between flat and fibrous landscapes opens new windows into cell behavior and the diseases that affect them. The findings were published in the Proceedings of the National Academy of Sciences February 27. The work received funding from the National Science Foundation and support from the Virginia Tech Institute for Critical Technology and Applied Science and the Virginia Tech Macromolecules Innovation Institute.
Cell division, called mitosis, is essential for the development, repair and biology of disease. A cell, at its most basic level, duplicates its chromosomes, which are then separated and evenly split between two daughter cells, each with its own complete set of genetic information. As new cells perform the same function, they form organs, heal wounds and replace dead cells, supporting the cycle of healthy tissues and organs.
But cell division doesn’t always go so smoothly. Sometimes cells divide unevenly or chromosomes may divide unevenly. When these misfires occur, the resulting cell will continue to duplicate copies of its faulty self, creating genetic defects that might cause widespread problems in a living body. These abnormalities are responsible for many prenatal congenital malformations and can contribute to the origin of cancer.
A better understanding of cellular mitosis increases our chances of diagnosing, treating and preventing these mitotic defects. Nain’s discovery puts valuable information in the hands of researchers by painting a full picture of what is happening at the cellular level in the body’s fibrous environment.
Movement, multiplication and division
At the microscopic level, cells move by means of an extracellular matrix (ECM), a three-dimensional network of organic matter that provides the framework for cells to form organs by resting on a solid foundation that holds them together.
Nain’s basic research focuses on recreating and studying this network, and his team’s previous studies of cell movement have shown how cells move along it. For a single fiber, a cell pulls itself at each end, walking the fiber like a tightrope. Two parallel fibers allow the cell to double these connections.
A dividing cell also uses the fibers around it. For a single fiber, each end of the cell adheres and pulls to create division. If a cell is in an environment with multiple fibers, it will likely attach to these as well. The ECM can traverse above and below the cell, providing a three-dimensional web on which the cells connect.
The number of fibers available for cells to attach to affects the timing of cell division and the types of defects a cell can produce. Cells take longer to divide on single fibers, and mitotic errors change with more attachments, creating a complex picture of the myriad ways a cell can fail.
This finding affects future research because the complex view of cell division errors has not been studied before in fibrous environments.
A new dimension for research
“Cell biology has mainly been studied on a Petri dish, which is a flat, two-dimensional surface,” Nain said. “Flat 2D is limited in physiological output because there are very few places in the body where the environment can be considered two-dimensional.”
The team found that observing cells in the 3D environment of an ECM produced new results beyond the capability of 2D petri dishes. In this work, the team asked a central question: how does the shape of a cell affect its division behavior?
Cell shape depends on how well a cell adheres to underlying substrates. For example, on a two-dimensional flat petri dish, a cell looks like a pancake. In a fibrous environment such as an ECM, shapes range from elongated airfoils to kites, depending on the number of fibers and their architecture. While a cell can adhere above and below the fiber plane to hanging fibers, a flat surface causes the cell to flatten and form outward connections. This flattening causes the cell to behave differently as it swells and divides.
Schematic of a rounded cell body attached to a single fiber and held together by cables of actin-retracting fibers (red) connecting adhesion clusters (green) to the cell cortex (blue). Image courtesy of Amrinder Nain.
When a rounded cell body divides, it is held in place by organic cables that connect the cell body, or cortex, to the fibers. On single fibers, near-perfect spherical cell bodies are held in place by two sets of cables, giving the rounded cell body maximum freedom to move around in 3D. As the number of fibers in the network increases, the number of places a cell can adhere also increases. This results in multiple cable complexes that restrict the 3D movement of the rounded cell body.
This simple mechanical effect highlights the significant difference between petri dish and ECM. On a petri dish, monopolar spindle defects, which represent incomplete separation of the spindle pole (or centrosome), do not occur often. However, when a cell is in a single fiber environment with two cable attachment sites, monopole pin faults increase.
These results literally revolutionize the study of cells: in the environment of a Petri dish, certain defects that occur during cellular mitosis cannot occur in the same way as in a living body.
“While bipolar splitting, the most common and error-free mode of splitting, dominates splitting outcomes in fibrous environments, our work shows a change in monopolar and multipolar defects by altering the number of fibers at which cells attach. attach,” Nain said. “It offers insight into how cell division might occur in actual living tissue.”
Nain hopes that the new perspective provided by this fundamental experimental and computational work will provide insight into how to treat genetic diseases and disorders.
“With the fiber networks, we provide more detail to a complete in vivo picture, by filling in some missing information, and using our multidisciplinary approach, we would like to ask specific questions regarding mitotic biology as we move forward,” a- he declared.
The multidisciplinary team assembled for this project includes leading experts, including cell division biologist Jennifer DeLuca, a professor at Colorado State University; theorist and biophysicist Nir Gov, professor at the Weizmann Institute of Science, Israel; and theorist and computer expert Raja Paul, professor at the Indian Association for the Culture of Science (IACS), India. The publication’s first author was Aniket Jana, now a postdoctoral fellow at the University of Maryland, College Park. Other student members involved in this study include Hoanan Zhang and Atharva Agashe from the Department of Mechanical Engineering at Virginia Tech, Ji Wang from the Department of Biomedical and Mechanical Engineering at Virginia Tech, and Apurba Sarkar from IACS, India.
