It's long been assumed that when a parent cell divides into two daughter cells, the parent assumes a spherical shape, which then splits into two cells that have roughly the same, round size. But a new study reported in Science has suggested that not all cells become spherical and rounded during division, and in the body, it doesn't usually work that way. Instead, the daughter cells aren't typically round after division, and they are asymmetrical.
Once thought to be a characteristic of stem cells, this work has suggested that asymmetric cell division plays an important role in the formation of different tissues and organs.
The research has indicated that a parent cell's shape prior to division can determine whether it will generate asymmetrical or symmetrical cells after division. If a cell is shorter and wider, it tends to produce daughter cells that are similar in shape and somewhat symmetrical. However, if a cell is long and thin it will usually generate asymmetrical daughter cells that are differently shaped.
"The phenomenon of mitosis, or cell division, is one of the fundamentals of life and a basic biological concept which is taught from school age. 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," said senior study author Dr. Shane Herbert, a senior research fellow at The University of Manchester.
"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."
When the researchers observed tissue formation in zebrafish embryos (which are transparent in their early hours of life), they saw migrating cells forming strands; fast moving cells were in the lead, while slower cells were in the back. If the faster cell at the front divided, it did so asymmetrically, to make another fast cell at the front, and a slower cell in the back.
With a technique called micropatterning, in which cells are made to form specific shapes, the researchers could then observe how different cell shapes influenced the resulting cell shape after a round of division.
The findings may have implications for the study of a variety of diseases, such as cancer. If cancer cells divide asymmetrically, it can boost metastasis, when cancer spreads and becomes far more deadly.
The work may also help scientists advance regenerative medicine; if a tissue or organ forms through asymmetrical cell division, the cell types that are used to repair damage or the genetic programs given to cells could improve regeneration techniques.
Sources: University of Manchester, Science