Growing droplets in the matrix

Date:
October 4, 2021
Source:
Max Planck Institute for Dynamics and Self-Organization
Summary:
The mechanism of molecular self-organization was assessed in a
new model.

In their study, scientists simulated how environmental factors
such as temperature influence the size of oil droplets in elastic
matrices. The study will also help understanding droplet formation
in biological cells, where biological molecules self-organize
in condensates.



FULL STORY ==========================================================================
In biology, proper regulation of the cell's interior is crucial to
ensure the function of biological processes. Yet, cells can be very
complex structures with several thousand different types of molecules
and millions of protein copy numbers. To organize this vast complexity,
several mechanisms are required to create sub-cellular environments
providing both defined and dynamic conditions.

For example, cellular organelles enable the segregation of cellular environments due to demarcation via membranes. However, also in the
crowded cellular matrix a structured organization of biomolecules
is required. There, so-called biomolecular condensates with a defined
molecular composition can form spontaneously. Prominent examples of this phenomenon include stress granules and transcriptional condensates. These condensates are surrounded by elastic structural elements in the cell, including the cytoskeleton and chromatin in the nucleus. The question
is: how are the condensates affected by the elastic structures and could
the cell use this interaction to exert control in the dynamic cellular environment?

==========================================================================
A model provides access to the realm of molecular organization As it
is in practical terms not possible to follow the detailed interaction
of millions of molecules in a cell in real-time, researchers use models describing individual facets of the phenomenon. "We are using oil droplets
to represent the material in the cytosol and a polymer mesh to mimic the biological scaffold" explains Estefania Vidal-Henriquez, first-author of
the study. "The dynamic development of the droplet size under certain conditions gives us information on how biological molecules would be
arranged in a cellular environment." The model describes the distribution
of different droplet sizes and their relative abundance. Moreover, it
considers that the surrounding matrix might be broken -- which would
refer to a rearrangement of the biological scaffold. This means that
the biomolecular condensates are not limited by the mesh size of its surrounding, but are capable of growing beyond.

Phase separation as the key mechanism A powerful concept to explain the
growth of such condensates is phase separation. Briefly, depending on
the conditions, two substances will be either mixed or coexist separated
from each other. Multiple factors may influence phase separation in
biology, such as pH, concentration, or temperature. In the model, the researchers used a temperature modulation to investigate the effect of
phase separation and droplet formation. Slowly lowering the temperature
of the system, a spontaneous nucleation of oil droplets was observed,
which were growing bigger in time by absorbing the material around
them. Interestingly, at a faster cooling speed more, but smaller droplets occur. Hence, the speed at which an external factor of influence changes
plays a crucial role in structure formation.

"With our model, we describe how the molecular composition can be arranged
on the microscale on an elastic matrix" summarizes David Zwicker, senior
author of the study and group leader at the MPIDS. Regarding the effect
of temperature modulation, he adds: "We expect similar behavior for biomolecular condensates which often form as a response to changes in temperature, pH, or protein concentration in cells." The model provides
the foundation to describe the formation of microscopic patterns in both technical and biological context.

========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Dynamics_and_Self-Organization.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Estefania Vidal-Henriquez, David Zwicker. Cavitation controls
droplet
sizes in elastic media. Proceedings of the National Academy of
Sciences, 2021; 118 (40): e2102014118 DOI: 10.1073/pnas.2102014118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211004104129.htm

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