Non-sequential and multi-step splicing of the dystrophin transcript

Area of Science:

• Molecular Biology
• Genetics
• Transcriptomics

Background:

• The dystrophin gene (DMD) is the longest human gene, featuring a large 2.2 Mb transcript.
• Its long introns and co-transcriptional splicing present unique challenges and opportunities for studying splicing mechanisms.
• Understanding splicing of long introns is crucial for comprehending gene expression regulation.

Purpose of the Study:

• To characterize the splicing patterns of dystrophin transcripts in human skeletal muscle cells.
• To investigate the order of intron removal and the prevalence of multi-step splicing.
• To identify novel splicing events, such as exon blocks, in long human transcripts.

Main Methods:

• Ultra-deep transcript sequencing of dystrophin transcripts from three human skeletal muscle cell lines.
• Coverage and read pair analyses to determine intron removal order.
• Computational and experimental validation of splicing events.

Main Results:

• Approximately 40% of introns were not removed sequentially during dystrophin transcript splicing.
• Non-consecutive intron removal was observed, leading to the formation of "exon blocks" (3+ joined exons flanked by unspliced introns).
• Multi-step splicing events were identified as a common mechanism for removing individual introns.

Conclusions:

• Multi-step intron removal is a general feature of mRNA splicing in human transcripts, exemplified by the dystrophin gene.
• The discovery of exon blocks provides new insights into the complexity of RNA processing.
• This research advances our understanding of splicing dynamics in long human genes.