Surprising! Far from being an ordered process, organelle growth is random burst growth

Eukaryotic cells—the cells that make up most of life as we know it, including all animals, plants, and fungi—are highly structured objects
.

These cells assemble and maintain smaller internal parts of themselves: membrane-bound organelles, such as the nucleus that stores genetic information, or mitochondria
that produce chemical energy.
But there's still a lot to be learned about how they organize themselves into these spatial compartments
.

Physicists at Washington University in St.
Louis have conducted new experiments showing that eukaryotic cells can strongly control average fluctuations
in organelle size.
By demonstrating that the size of organelles defers to the universal proportional relationship theoretically predicted by the scientists, their new framework shows that organelles grow
randomly from a limited pool of building blocks.

The study was published Jan.
6 in
Physical Review Letters.

Shankar Mukherji, assistant professor of physics in the College of Arts and Sciences, said: "In our work, we believe that the growth steps of organelles are far from an orderly 'brick-to-brick' assembly, but random bursts
.
"

"This burst radically limits the precision of controlling organelle size, but also keeps the noise of organelle size within a narrow window
," Mukherji said.
"Burst growth provides a general biophysical mechanism by which cells can maintain an average, reliable and plastic organelle size
.
"

Organelles must be flexible enough to allow cells to grow or contract
as needed by the environment.
However, the size of the organelle must be kept within
certain limits.
Biologists have previously identified certain molecular factors that regulate organelle size, but this study provides new insights
into the quantitative principles of organelle size control.

While this study used budding yeast as a model organism, the research team is excited to explore how these assembly mechanisms can be exploited
in different species and cell types.
Mukherji says they plan to study how these robust patterns could teach us how we can harness organelle assembly for bioengineering applications, and how to find defects
in organelle biogenesis in the context of disease.

Mukherji said: "The pattern of organelle size robustness is the same
for budding yeast and human iPS cells.
" "The underlying molecular mechanisms that produce these outbreaks have not been fully elucidated and are likely to be organelle-specific as well as
species-specific.
"

This study was supported
by the National Institutes of Health (NIH R35GM142704).

Journal Reference:

1. Kiandokht Panjtan Amiri, Asa Kalish, Shankar Mukherji.
   Robustness and Universality in Organelle Size Control.
   Physical Review Letters, 2023; 130 (1) DOI: 10.
   1103/PhysRevLett.
   130.
   018401