Introduction to Gene Splicing

Introduction to Splicing

• Splicing is a crucial step in gene expression.
• It involves the removal of non-coding sequences (introns) from pre-mRNA molecules.
• Introns are interspersed within coding sequences (exons).
• The remaining exons are joined together to form mature mRNA.
• This mature mRNA serves as a template for protein synthesis.

The Splicing Process

• Splicing is catalyzed by a large complex of proteins and small nuclear RNAs (snRNAs) called the spliceosome.
• The spliceosome recognizes specific sequences at the 5' and 3' splice sites of introns.
• Key splicing steps include:
  • Spliceosome recognition of splice sites.
  • Formation of a lariat structure at the intron's 5' splice site.
  • Excision of the intron as a lariat structure.
  • Joining the two exons together.

Alternative Splicing

• Alternative splicing is a process where a single gene produces multiple different mRNA molecules.
• Different combinations of exons are joined together during splicing.
• This results in proteins with different structures and functions from the same gene.
• It's a major mechanism for increasing protein diversity encoded in a genome.

Mechanisms of Alternative Splicing

• Alternative splicing events occur through various mechanisms:
  • Exon skipping: An exon is removed entirely.
  • Exon inclusion/exclusion: Different combinations of exons are included or excluded.
  • Alternative 5' or 3' splice site selection: Different splice sites are used, altering the protein-coding region's start or end.
  • In-frame alternative splicing: An in-frame insertion or deletion in the protein sequence, potentially changing the protein's function.

Regulation of Alternative Splicing

• Alternative splicing regulation is complex, often controlled by:
  • Specific splicing factors: Proteins that bind to pre-mRNA and influence splice site selection.
  • Transcription factors: Factors that bind to DNA, influencing the expression of splicing factor genes.
  • RNA-binding proteins: Proteins that bind to mRNA and influence splicing outcomes.
  • Environmental factors: External factors affecting splicing patterns.

Biological Significance of Alternative Splicing

• Multiple protein isoforms from a single gene increase protein diversity and allow for complex proteomes.
• This facilitates cell type-specific protein production.
• It plays a key role in development, differentiation, and disease.

Impact of Alternative Splicing on Diseases

• Dysregulation of alternative splicing can lead to various diseases.
• Mutations in splicing factor genes result in aberrant splicing patterns.
• Splicing errors significantly affect protein production, potentially causing misfolded proteins or loss of crucial isoforms.
• Aberrant alternative splicing is linked to a wide range of human diseases, including neurological disorders, cardiovascular diseases, and cancers.