What You Learned About Cell Division Is Probably Wrong

If you took high school biology, you probably learned about cell division: a crucial process in all life forms officially called mitosis. For over one hundred years, students have learned that during mitosis, a parent cell becomes spherical before dividing into two daughter cells of the same size and shape. A new study, however, might rewrite many, many biology textbooks.

Researchers revealed that mitosis doesn’t always feature cell rounding (when a parent cell becomes spherical), meaning that the resulting daughter cells aren’t always symmetrical, nor do they carry the same function. Their work is detailed in a study published Thursday in the journal Science, and holds important implications for understanding cell division in diseases such as cancer.

“Students learn that when a cell divides, it will generate a uniform spherical shape. Our study, however, shows that in real living organisms, it is not as simple as that,” Shane Herbert, co-lead author of the study and a researcher at the University of Manchester’s faculty of Biology, Medicine and Health, said in a university statement.

In the new study, researchers observed blood vessel formation in zebrafish embryos. The growth of new vessels consists of slow-moving cells led by a single fast-moving cell. When the lead cell underwent mitosis, it didn’t become spherical or experience rounding. The asymmetrical division allowed it to form two different cells: one slow-moving cell and one fast-moving cell to take the lead in the parent cell’s place. Previously, scientists had mainly associated asymmetric cell division with specialized cells called stem cells.

“Using transparent 1-day old zebrafish embryos allows us to study a dynamic process like cell division inside a living organism,” said Holly Lovegrove, co-lead author of the study and a lecturer in cardiovascular sciences at The University of Manchester. “We are therefore able to make movies of this fundamental cell behaviour and in doing so reveal exciting new aspects of how tissues grow.”

Furthermore, the researchers noted that the shape of the parent cell can determine whether its division will be symmetrical or asymmetrical. For example, they observed that shorter and wider cells were more likely to become spherical and split into two similar daughter cells. In contrast, longer and thinner cells didn’t “round-up,” and as a result, divided asymmetrically.

To further investigate this, Herbert, Lovegrove, and their colleagues manipulated the size of human parent cells via micropatterning. “Micropatterning allows us to generate specifically shaped microscopic patches of proteins that cells can stick to,” explained Georgia Hulmes, co-first author of the study and a postdoctoral research associate at The University of Manchester’s School of Biological Sciences. “The cells will then take the shape of the patch. This therefore allows us to change the shape of the cells and test how these shapes impact on the subsequent cell division.”

“Our research suggests that the shape of the cell before it divides can fundamentally direct whether a cell rounds, and importantly, if its daughters are symmetric or asymmetric both in size and function,” Herbert said.

As a result, scientists might one day be able to generate cells with different functions by controlling the shape of their parent cells. More broadly, their analyses suggest that asymmetric divisions play an important role in the creation of different tissues and organs. The study also holds important implications for diseases such as cancer, in which asymmetric division could lead to different cell behaviors potentially associated with cancer progression.

In the meantime, our thoughts are with all the students, parents, and school administrators who might soon have to spend an exorbitant amount of money on updated textbooks.