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Translational suppression by trinucleotide repeat expansion at FMR1
1Howard Hughes Medical Institute, Emory University School of Medicine, Atlanta, GA 30322.
Science (New York, N.Y.)
|May 5, 1995
Summary
Fragile X syndrome arises from trinucleotide repeat expansion in the FMR1 gene. Beyond 200 repeats, this expansion stalls protein production, leading to diminished FMR protein levels and translational inhibition.
Area of Science:
- Genetics
- Molecular Biology
- Neuroscience
Background:
- Fragile X syndrome is a genetic disorder caused by the expansion of CGG trinucleotide repeats in the FMR1 gene's 5'-untranslated region.
- The precise mechanism by which repeat expansion leads to reduced FMR protein levels is not fully understood.
Purpose of the Study:
- To investigate the relationship between CGG repeat length in the FMR1 gene and FMR protein levels.
- To elucidate the molecular mechanisms underlying translational inhibition in Fragile X syndrome.
Main Methods:
- Analysis of FMR1 messenger RNA and FMR protein levels in fibroblast subclones with varying CGG repeat lengths (57-285 repeats).
- Investigation of ribosomal subunit association with FMR1 transcripts using stalled 40S ribosomal subunits as an indicator.
Main Results:
- Fibroblast subclones with up to 285 CGG repeats maintained normal FMR1 messenger RNA levels.
- FMR protein levels were significantly reduced in transcripts containing more than 200 CGG repeats.
- Transcripts with expanded repeats were associated with stalled 40S ribosomal subunits, indicating impaired translation.
Conclusions:
- CGG repeat expansion beyond 200 repeats in the FMR1 gene leads to a structural RNA transition that impedes ribosomal subunit migration.
- This impediment results in translational inhibition, explaining the diminished FMR protein observed in Fragile X syndrome.
- The findings provide a molecular mechanism for how trinucleotide repeat expansion causes disease pathology.