TDP-43 NTD can be induced while CTD is significantly enhanced by ssDNA to undergo liquid-liquid phase separation

Abstract

TDP-43 inclusions are characterized by a large spectrum of neurodegenerative diseases such as ALS and Alzheimer's. Functionally, TDP-43 is engaged in forming dynamic granules via liquid-liquid phase separation (LLPS), which is now recognized to be a general principle for organizing a variety of cellular membrane-less organelles. TDP-43 is composed of the N-terminal domain (NTD) adopting an ubiquitin-like fold, two RRMs and C-terminal domain (CTD) with the low-complexity (LC) prion-like sequences. Previously, only the CTD was found to undergo LLPS to form dynamic liquid droplets with relatively small numbers and sizes. Here we found for the first time that ssDNA can induce the NTD as well as significantly enhance the CTD to undergo LLPS. Further systematic investigations with 10 ssDNA of different sequences and lengths reveal that two distinct mechanisms exist respectively for the ssDNA-mediated LLPS of the NTD and CTD. As most, if not all functions of TDP-43, are involved in contacting nucleic acids including ssDNA, our results imply that nucleic acids might mediate the physiological functions and pathological roles of TDP-43 by previously-unappreciated mechanisms.

Keywords: Amyotrophic lateral sclerosis (ALS); Liquid-liquid phase separation (LLPS); Prion-like domain; Single-stranded DNA (ssDNA); TDP-43; Ubiquitin-like fold.