Spectrum of splicing errors caused by CHRNE mutations affecting introns and intron/exon boundaries

Area of Science:

• Genetics
• Molecular Biology
• Neuroscience

Background:

• Congenital myasthenic syndromes (CMS) are caused by mutations in the CHRNE gene, which encodes the muscle nicotinic acetylcholine receptor epsilon subunit.
• The splicing consequences of only three of the eight reported intronic splice site mutations in CHRNE have been characterized.

Purpose of the Study:

• To investigate the splicing consequences of previously reported and novel splicing mutations in the CHRNE gene.
• To understand how intron length and specific sequence features affect CHRNE gene splicing.

Main Methods:

• Analysis of four previously reported and five novel splicing mutations in the CHRNE gene.
• Introduction of normal and mutant genomic CHRNE sequences into COS cells for functional analysis.

Main Results:

• Short introns (82-109 nucleotides) promote intron retention, while medium to long introns (306-1210 nucleotides) favor exon skipping.
• A G-->T substitution at the 3' end of exon 8 leads to exon skipping due to a failure to compensate for an exonic mutation at position -1.
• A 16 bp duplication creates two 3' splice sites, resulting in the silencing of the downstream site, consistent with the scanning model of splice site recognition.

Conclusions:

• Intron length is a critical determinant of splicing outcomes (retention vs. skipping) in the CHRNE gene.
• Specific sequence features, such as mismatches at splice junctions and duplications creating alternative splice sites, can lead to aberrant splicing and potentially disease.
• These findings provide insights into the molecular mechanisms underlying CHRNE-related congenital myasthenic syndromes.