by Scientists led by James Umen, Ph.D., from the Donald Danforth Plant Science Center, have made a groundbreaking discovery regarding the mechanism used by the single-celled green alga Chlamydomonas to control cell division. The research team found that the number of divisions a mother cell undergoes to restore its daughters to the correct starting size deviates from what was previously assumed. Mother cells rarely divide just once; instead, they either do not divide at all or divide two or more times. This bias against a single division has significant implications for understanding the evolution of multicellular life and offers new opportunities for engineering algal cells for improved biofuel yields and high-value products.
The study, titled “A Cell-Based Model for Size Control in the Multiple Fission Alga Chlamydomonas reinhardtii,” was published on November 9, 2023, in the journal Current Biology.
Chlamydomonas cells, along with other algae and single-celled protists, have the ability to grow very large before dividing. This growth and division pattern allows them to optimize their use of light and nutrients. However, it creates a size control challenge. Under certain conditions, cells only double in size before dividing once. But under more favorable conditions, cells can grow over ten times their starting size and need to undergo multiple divisions to produce daughters of the correct size. This size variability presented a puzzle, which was resolved with the evolution of a mechanism in Chlamydomonas that allows cells to assess their size and accurately count the required number of divisions.
Researchers had always assumed that the division pattern was determined by a simple relationship between the mother cell’s size and the number of divisions. Models based on this assumption could accurately predict the behaviors of entire cell populations. However, by examining the division behaviors of thousands of individual cells of varying sizes, the research team discovered an unexpected scarcity of cells dividing just once. Instead, cells that should have divided once either chose not to divide at all, or only became capable of division after doubling in size.
To make sense of this finding, the team used mathematical modeling to develop a more accurate predictive model for the cells’ behavior. At the same time, another group of researchers delved into the genetic mechanisms responsible for the observed counting bias. They found that the retinoblastoma tumor suppressor pathway, a genetic mechanism that controls cell division in algae, plants, and humans, plays a crucial role in preventing single divisions.
While the understanding of how the retinoblastoma pathway functions in algae is still in its early stages, the discovery of a mechanism that introduces bias in cell division behavior suggests that cells modified their division behavior as an essential step in the evolution of multicellular life, according to Dianyi Liu, Ph.D., a postdoctoral associate involved in the study at the Danforth Center.
Relatives of Chlamydomonas that exhibit multicellular behavior not only skip the option of undergoing a single division, but can also delay division until they have grown significantly in size. This allows a single cell to rapidly produce a new multicellular individual with hundreds or even thousands of cells, a vital ability for survival and fitness. The bias against a single division observed in Chlamydomonas was likely present in the direct ancestors of its multicellular relatives and was further amplified as they evolved greater size and complexity. Although the reason behind the evolution of this bias remains unclear, understanding this mechanism and its genetic control has practical implications in algal biotechnology. Cell size can impact yields of high-value products and even the susceptibility of algae to predation by filter feeders in open pond cultures.
Moving forward, the research team’s focus is to understand and model the specific mechanisms employed by the retinoblastoma pathway to alter cell division behavior in algae. This work may lead to advancements in algal biotechnology and provide insights into how the retinoblastoma pathway prevents cancer in human cells and regulates the timing and location of cell division in plants.
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1. Source: Coherent Market Insights, Public sources, Desk research
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