Demixing is a default process for biological condensates formed via phase separation

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Excitatory and inhibitory synapses segregate on neurons, but the mechanisms remain unclear.
• Understanding the compartmentalization of postsynaptic structures is crucial for neuronal function.

Purpose of the Study:

• To investigate the mechanisms underlying the segregation of excitatory and inhibitory postsynaptic densities (e/iPSDs).
• To explore the role of phase separation in cellular compartmentalization.

Main Methods:

• Biochemical reconstitutions in vitro and in live cells.
• Molecular tagging and tracking of postsynaptic scaffold proteins.

Main Results:

• Excitatory and inhibitory postsynaptic densities (e/iPSDs) spontaneously segregate into distinct liquid-like condensates through phase separation.
• Targeting inhibitory scaffold gephyrin to excitatory condensates resulted in its expulsion upon formation of inhibitory condensates.
• Demixing, rather than diffusion-driven mixing, is the default process for biomolecules in condensates.

Conclusions:

• Phase separation drives the formation of distinct e/iPSD condensates, explaining their segregation.
• This process generates specific biomolecular compartmentalization not achievable in dilute solutions.
• Demixing is a fundamental principle governing biomolecular organization in cellular condensates.