Tracking the morphological diversity of hnRNPA1 prion-like domain condensates.

Abstract

Pathological protein aggregates in diseased tissues of neurodegenerative diseases have distinct morphologies, such as the round hyaline inclusions and skein-like filaments that typify Amyotrophic Lateral Sclerosis (ALS) histology and the neurofibrillary tangles and circular Lewy body-like structures in Alzheimer's disease (AD). Heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), a member of the ubiquitously expressed RNA-binding proteins involved in RNA metabolism, has been implicated in ALS and AD pathogenesis. How the formation of hnRNPA1 inclusions correlates with ALS and AD pathologies remains a mystery. To monitor the morphological evolution of hnRNPA1 prion-like C-terminal domain (hnRNPA1PrD), we employed a combination of biophysical techniques, including confocal time-lapse (4D) and fluorescence lifetime imaging microscopy (FLIM). Our findings suggest hnRNPA1PrD aggregates can proceed directly from a dilute phase and/or via a droplet intermediate, which can age into gel-like condensates or starbursts with filaments that elongate and bifurcate via prion-like infectivity. Modulation of homotypic and heterotypic solution conditions generates diverse hnRNPA1PrD inclusion morphologies as observed in neurodegeneration.