ALS-causative mutations in FUS/TLS confer gain and loss of function by altered association with SMN and U1-snRNP

Area of Science:

• Molecular Biology
• Neuroscience
• Genetics

Background:

• Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease.
• Mutations in the RNA-binding protein FUS/TLS are a known cause of familial ALS.
• The U1-snRNP and SMN complexes are vital for RNA processing and cellular function.

Purpose of the Study:

• To investigate the interaction of FUS/TLS with U1-snRNP and SMN complexes.
• To determine how ALS-causative FUS/TLS mutations affect these interactions and cellular functions.
• To identify potential converging disease mechanisms between ALS and spinal muscular atrophy (SMA).

Main Methods:

• Co-immunoprecipitation assays to assess protein-protein interactions.
• Analysis of SMN complex integrity (Gems) and small nuclear RNA levels.
• Global RNA analysis to evaluate splicing activity.
• Identification of RNA splicing signatures in patient-derived fibroblasts.

Main Results:

• ALS-linked FUS/TLS mutants show enhanced binding to SMN, leading to dysregulation and loss of Gems.
• These mutants exhibit reduced association with U1-snRNP.
• Mutant FUS/TLS impairs global RNA splicing activity, and a common splicing signature is observed in ALS patient cells.
• ALS-causative mutants demonstrate both gain-of-function (SMN dysregulation) and loss-of-function (reduced RNA processing) properties.

Conclusions:

• ALS-causative FUS/TLS mutations disrupt interactions with U1-snRNP and SMN complexes.
• These disruptions lead to impaired RNA processing and SMN pathway dysregulation, contributing to ALS pathogenesis.
• The findings suggest converging molecular mechanisms in ALS and SMA, highlighting the importance of RNA processing pathways in neurodegeneration.