Eukaryotic cells are highly structured objects that make up the majority of life as we know it, including all animals, plants, and fungi.
These cells build and maintain their own internal components, such as membrane-bound organelles like nuclei, which store genetic information, or mitochondria, which produce chemical energy. However, much remains unknown about how they organize themselves into these spatial compartments.
New experiments by biophysicists at Washington University in St. Louis show that eukaryotic cells can robustly control average fluctuations in organelle size. By showing that the sizes of organelles follow a universal scaling relationship predicted by theory, the scientists’ new framework suggests that organelles grow in random bursts from a limited number of building blocks.
Organelle Stochastic Bursts
The researchers’ findings suggest that rather than being an orderly brick-by-brick process of assembly, the steps by which organelles are formed occur in stochastic bursts.
“Such bursts fundamentally limit the precision with which organelle size is controlled but also maintain noise in organelle size within a narrow window. Burstlike growth provides a general biophysical mechanism by which cells can maintain, on average, reliable yet plastic organelle sizes,”
said Shankar Mukherji, assistant professor of physics.
Organelles must be adaptable enough to allow cells to grow or shrink in response to environmental cues. However, the size of organelles must be kept within certain limits.
Biologists have previously identified specific molecular factors that regulate organelle sizes, but this study adds to the understanding of the quantitative principles underlying organelle size control.
Organelle Size Robustness
Although the yeast Saccharomyces cerevisiae was used as a model organism in this study, the team is eager to investigate how these assembly mechanisms are used in various species and cell types.
Mukherji said that they wanted to find out what these robustness patterns can teach us about how organelle assembly could be used in bioengineering and how to detect errors in organelle biogenesis when there is disease.
“The pattern of organelle size robustness is shared between budding yeast and human iPS cells. The underlying molecular mechanisms producing these bursts are yet to be fully elucidated and are likely to be organelle-specific and potentially species-specific,”
- Kiandokht Panjtan Amiri, Asa Kalish, and Shankar Mukherji. Robustness and Universality in Organelle Size Control. Phys. Rev. Lett. 130, 018401 (6 January 2023)