Retrotransposition Events Shape the Evolution of the Ataxin-3 Gene Family in Primates

Area of Science:

• Evolutionary genetics
• Neurodegenerative diseases
• Molecular biology

Background:

• Polyglutamine spinocerebellar ataxias (SCAs) are neurodegenerative diseases linked to expanded CAG repeats in specific genes.
• Machado-Joseph disease (MJD/SCA3), the most common SCA, is caused by mutations in the ATXN3 gene and currently lacks effective treatments.
• Paralogs of disease-associated genes can offer insights into disease mechanisms and potential therapeutic strategies.

Purpose of the Study:

• To identify and characterize new paralogs of the ATXN3 gene involved in MJD/SCA3.
• To investigate the evolutionary history and functional potential of ATXN3 paralogs using phylogenetic analysis.
• To explore the relevance of ATXN3 paralogs for understanding the pathogenic mechanisms of MJD/SCA3 and developing novel therapies.

Main Methods:

• Identification of ATXN3 retrotransposition events across primate evolution.
• Phylogenetic analysis of ATXN3 and its paralogs (ATXN3L1, ATXN3L2, ATXN3L0, ATXN3L3).
• Comparative analysis of gene sequences, conservation patterns, and (CAG)n interruption patterns.

Main Results:

• Three new ATXN3 paralogs (ATXN3L0, ATXN3L2, ATXN3L3) were identified, in addition to the previously known ATXN3L1.
• ATXN3 and ATXN3L1 are conserved in primates, showing significant amino acid identity and a conserved Josephin domain, suggesting functional redundancy.
• ATXN3L2 exhibits high nucleotide similarity to ATXN3, potentially producing a regulatory RNA, while ATXN3L0 and ATXN3L3 are likely non-functional or absent in humans.
• Analysis of (CAG)n interruption patterns elucidated the evolution of pathogenic repeat tracts in human ATXN3.

Conclusions:

• The discovery of ATXN3 paralogs provides new avenues for understanding MJD/SCA3 pathogenesis.
• The conserved ATXN3L1 suggests potential for therapeutic intervention by mimicking its function.
• Phylogenetic analysis of ATXN3 paralogs offers insights into the origin of disease-causing repeat expansions and aids in the search for targeted therapies.