Sau, A. | bioRxiv Science

bioRxiv2025

Clustering within a single-component biomolecular condensate

Biomolecular condensates (BMCs) are assemblies of hundreds to many thousands of macromolecules within cells that are organized without physical barriers. Condensate function is dictated not only by its molecular composition, but also by substructural organization and molecular mobility. One hypothesis for the onset of multiple protein aggregation diseases is that the increased densities of specific proteins within BMCs promotes the formation of solid inclusions. However, deciphering the internal structural and functional properties of BMCs at the nanoscale and identifying the initiating events of inclusion formation requires tools with high spatiotemporal precision. Here we show using single molecule and other microscopy approaches that single component Fused in Sarcoma (FUS) condensates exhibit confinement and contain clusters with higher FUS density even at early timepoints. Upon aging, condensates displayed altered physical properties and reduced monomer mobility, and yet most FUS monomers diffused throughout the condensate within seconds. While an increase in connectivity over time explains reduced mobility, the large fraction of molecules retaining high mobility suggests a sponge-like structure rather than a system-spanning network. These findings indicate that a pseudo-equilibrium between distinct structural connectivities can exist within simple condensates, suggesting the potential for substantial structural and functional complexity of BMCs at the nanoscale.

biophysics↗

bioRxiv2024

A series of spontaneously blinking dyes for super-resolution microscopy

Spontaneously blinking fluorophores permit the detection and localization of individual molecules without reducing buffers or caging groups, thus simplifying single-molecule localization microscopy (SMLM). The intrinsic blinking properties of such dyes are dictated by molecular structure and modulated by environment, which can limit utility. We report a series of tuned spontaneously blinking dyes with duty cycles that span two orders of magnitude, allowing facile SMLM in cells and dense biomolecular structures.

cell biology↗

bioRxiv2021

Identifying locations susceptible to micro-anatomical reentry using a spatial network representation of atrial fibre maps

Micro-anatomical reentry has been identified as a potential driver of atrial fibrillation (AF). In this paper, we introduce a novel computational method which aims to identify which atrial regions are most susceptible to micro-reentry. The approach, which considers the structural basis for micro-reentry only, is based on the premise that the accumulation of electrically insulating interstitial fibrosis can be modelled by simulating percolation-like phenomena on spatial networks. Our results suggest that at high coupling, where micro-reentry is rare, the micro-reentrant substrate is highly clustered in areas where the atrial walls are thin and have convex wall morphology. However, as transverse connections between fibres are removed, mimicking the accumulation of interstitial fibrosis, the substrate becomes less spatially clustered, and the bias to forming in thin, convex regions of the atria is reduced. Comparing our algorithm on image-based models with and without atrial fibre structure, we find that strong longitudinal fibre coupling can suppress the micro-reentrant substrate, whereas regions with disordered fibre orientations have an enhanced risk of micro-reentry. We suggest that with further development, these methods may have future potential for patient-specific risk stratification, taking a longitudinal view of the development of the micro-reentrant substrate. Author summaryAtrial fibrillation (AF) is the most common abnormal heart rhythm, yet, despite extensive research, treatment success rates remain poor. In part, this is because there is an incomplete understanding of the mechanistic origin of AF. In this paper, we investigate one proposed mechanism of AF, the formation of "micro-reentrant circuits", which can be thought of as a "short circuit", forming when electrically insulating fibrosis (structural repair tissue) infiltrates the space between heart muscle cells. Previously, such circuits have been found in experimental hearts, but identifying these circuits clinically is difficult. Here, we aim to take a small step towards developing computational methods for identifying where in the atria these circuits are most likely to form, drawing on techniques from network science. Our approach indicates that a number of factors are key to determining where circuits form, most notably the thickness of the heart muscle, and the alignment of muscle fibres.

physiology↗