Sequence Determinants of TDP-43 Ribonucleoprotein Condensate Formation and Axonal Transport in Neurons

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Mutations in the TAR DNA-binding protein 43 (TDP-43) are a primary cause of amyotrophic lateral sclerosis (ALS).
• TDP-43 is essential for RNA metabolism and forms ribonucleoprotein (RNP) granules, which are critical for neuronal function.
• ALS-linked mutations promote aberrant phase transitions in TDP-43 RNP granules, impairing their dynamic properties and transport within neurons.

Purpose of the Study:

• To identify critical structural elements and residues in TDP-43 that determine its RNP granule transport and condensate formation in neurons.
• To elucidate the molecular mechanisms by which ALS-associated TDP-43 mutations lead to motor neuron degeneration.

Main Methods:

• Comparative analysis of ALS-linked TDP-43 mutations and variants.
• Investigating the impact of specific residue substitutions on TDP-43 RNP granule motility (anterograde and retrograde transport).
• Assessing the role of structural domains, including the alpha-helical domain, LARKS motif, and RGG motif, in TDP-43 function.

Main Results:

• Specific mutations (A315T, Q343R) and substitutions of aromatic residues in the alpha-helical domain and LARKS motif severely impair TDP-43 RNP granule transport.
• Phenylalanine residues in LARKS and tryptophan in the alpha-helical domain are vital for TDP-43 RNP transport.
• Disruption of the RGG motif in the low-complexity domain (LCD) significantly reduces directed transport and velocity of TDP-43 RNP granules.
• Mutations in disordered regions also affect TDP-43 RNP granule motility, though generally to a lesser extent than those in core structural elements.

Conclusions:

• The alpha-helical domain, phenylalanine residues within LARKS, and the RGG motif are key determinants of TDP-43 RNP transport.
• These structural elements likely mediate the recruitment of motor and adaptor proteins essential for axonal transport.
• The findings provide a mechanistic link between TDP-43 dysfunction and the axonal transport deficits observed in ALS.