New Discovery on How Green Algae Count Cell Divisions Illuminates Key Step Needed for The Evolution of Multicellular Life
Published:26 Jan.2024 Source:Donald Danforth Plant Science Center
Chlamydomonas cells, like those of many other algae and single-celled protists, can grow very large before they divide. This atypical growth and division pattern lets them make optimal use of light and nutrients, but also creates a problem in size control. The size variability presents a conundrum which was solved by the evolution of a mechanism in Chlamydomonas that enables cells to assess their size and count out the correct number of cell divisions. By looking at division behaviors of thousands of individual cells of varying sizes, researchers found an unanticipated dearth of cells dividing just once. Instead, cells that should have divided once opted to not divide at all, and most cells only became able to divide when they had more than doubled in size.
The team used mathematical modeling to come up with a more accurate predictive model for the behavior of the cells. They discovered that a well-known, but still poorly-understood genetic mechanism for controlling cell division found in algae, plants and humans -- called the retinoblastoma tumor suppressor pathway -- plays a critical role in preventing just one division. Cells modified their division behavior as an important step in the evolution of multicellular life. Multicellular relatives of Chlamydomonas not only skip the option to undergo one division but can prevent division until they have grown many times in size. This enables a single cell to rapidly produce a whole new multicellular individual with hundreds or even thousands of cells, an ability that is critical for fitness and survival.
The bias against one division researchers observed in Chlamydomonas was very likely present in direct ancestors of its multicellular relatives and was further amplified as they evolved greater size and complexity. Looking forward, the team is now focused on understanding and modeling the specific mechanisms used by the retinoblastoma pathway to alter cell division behavior in algae, work that may lead to advances in algal biotechnology and even shed light on how the retinoblastoma pathway keeps human cells from developing cancer and prevents plant cells from dividing at the wrong time and place.