Disentangling a new paradigm for mutual homeostasis of aggregation-prone proteins

The dosage of proteins must be regulated in cells, especially for those containing low complexity domains (LCD-proteins) due to their propensity for condensation and aberrant aggregation in neurodegeneration.

We recently identified a new mechanism, ‘interstasis’, that achieves dosage-responsive co- regulation of LCD-proteins via RNA-protein condensates called nuclear speckles.

Speckles can sequester excess LCD-proteins, along with the mRNAs that encode them, thus preventing protein production until the cell lowers their combined dosage.

I will apply innovative biophysical tools exploiting microfluidics and atomic force microscopy applied to reconstituted speckles to first ask how they achieve selectivity for mRNAs that encode LCD-proteins.

I will then address a new paradigm whereby this selective protein-RNA condensation contributes to mutual homeostasis of LCD-proteins, using cellular and reconstituted systems.

I will modulate the threshold of interstasis in neuronal models of amyotrophic lateral sclerosis and measure proteome-wide solubility changes using mass spectrometry.

To reveal the interactions underlying these changes, I will simulate interstasis and disease states in vitro and study the biophysical changes of speckles and specific LCD-proteins, by modulating stoichiometries, LCD multivalency, and post-translational modifications.

This will provide a crucial understanding of the roles of RNA- protein condensates in counteracting aggregation of LCD-proteins in the early stages of neurodegeneration.