A Deep Exon Cryptic Splice Site Promotes Aberrant Intron Retention in a Von Willebrand Disease Patient

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• A single nucleotide mutation in exon 44 of the von Willebrand factor (VWF) gene leads to intron retention (IR) in a von Willebrand disease (VWD) patient.
• Previous research suggested altered secondary structure of exon 44 (E44) sequesters the normal splice donor site, causing IR.

Purpose of the Study:

• To investigate the mechanism of IR caused by a VWF gene mutation.
• To evaluate the roles of secondary structure and cryptic splice sites in E44 splicing.

Main Methods:

• Minigene splicing reporters were engineered with variations in secondary structure and cryptic splice site content.
• Splicing efficiency was analyzed in transfected K562 cells.

Main Results:

• A mutation-generated cryptic splice donor site in E44 was sufficient to induce significant IR.
• Altering secondary structure at the annotated splice site had minor effects on IR and shifted splice site usage.
• Competition between the annotated and cryptic splice sites was observed.

Conclusions:

• Mutant deep exon splice sites can interfere with proper splicing by inducing IR.
• The context-dependent introduction of cryptic splice donor motifs is crucial for IR induction.