Nuclear speckles are detention centers for transcripts containing expanded CAG repeats.

Area of Science:

• Genetics
• Molecular Biology
• Neuroscience

Background:

• Polyglutamine (polyQ) diseases are genetic disorders caused by expanded CAG repeats in genes.
• Mutant protein toxicity is a hallmark, but the role of mutant transcripts is increasingly recognized.
• Cellular models of polyQ diseases often exhibit distinct molecular features.

Purpose of the Study:

• To investigate the common molecular features of cellular models for polyQ diseases.
• To characterize the formation, number, and morphology of nuclear CAG RNA foci.
• To explore the relationship between CAG repeat length, RNA foci, and splicing factor interactions.

Main Methods:

• Fluorescence in situ hybridization (FISH) for qualitative and quantitative analysis of RNA foci.
• Comparison of CAG foci in polyQ disease models with CUG foci in myotonic dystrophy type 1.
• FISH combined with immunofluorescence to assess co-localization with MBNL1.

Main Results:

• Nuclear CAG RNA foci are a common feature in diverse polyQ disease cellular models.
• Foci number and morphology differ between polyQ diseases and myotonic dystrophy type 1.
• CAG repeat length positively correlates with foci number; CAA repeats do not form foci.
• Foci formation is independent of mutant protein presence and partially co-localizes with MBNL1.
• CAG repeat foci are located within nuclear speckles and depend on their integrity.

Conclusions:

• Nuclear CAG RNA foci are a conserved pathogenic feature in polyQ disease models, irrespective of mutant protein presence.
• RNA foci characteristics vary with repeat length and disease type, offering potential diagnostic markers.
• Partial MBNL1 co-localization suggests a mechanism for mild splicing deregulation in polyQ diseases.