Upstream non-AUG initiation and ribosomal -1 frameshifting in ATXN8OS CTA/CTG repeat-associated translation

Area of Science:

• Neurogenetics
• Molecular Biology
• RNA Translation

Background:

• Microsatellite repeat expansions are linked to neurodegenerative diseases like spinocerebellar ataxia type 8 (SCA8).
• The ATXN8OS gene contains expanded CTA/CTG repeats in SCA8, but its translation mechanism remains unclear.
• Previous studies reported repeat-associated non-AUG (RAN) translation from ATXN8, but not ATXN8OS.

Purpose of the Study:

• To investigate the occurrence and mechanisms of translation from the ATXN8OS transcript in spinocerebellar ataxia type 8.
• To explore how expanded CTA/CTG repeats influence ATXN8OS translation.
• To elucidate the role of the integrated stress response in ATXN8OS translation.

Main Methods:

• Utilized cell-free translation systems and cultured cells to study ATXN8OS translation.
• Employed mechanistic analyses to identify translation initiation sites and frameshifting events.
• Applied live-cell imaging at the single messenger RNA level to visualize ribosomal dynamics.
• Investigated the impact of integrated stress response activation on ATXN8OS translation.

Main Results:

• Demonstrated robust, AUG-independent translation of ATXN8OS in a repeat length-dependent manner.
• Identified non-AUG codon initiation upstream of repeats and ribosomal -1 frameshifting to the poly T-poly A (+2) frame.
• Observed enhanced ATXN8OS translation upon activation of the integrated stress response.
• Directly visualized ribosomal frameshifting during translation elongation at the single mRNA level.

Conclusions:

• Established the occurrence and molecular mechanisms of ATXN8OS translation from expanded CTA/CTG repeats.
• Provided direct evidence for non-AUG initiated and frameshifted translation of ATXN8OS.
• Highlighted the role of the integrated stress response in modulating ATXN8OS translation.
• Offered insights into the pathogenic processes underlying spinocerebellar ataxia type 8.