Causes of abnormal pigtail splicing

Abnormal pigtail splicing is primarily caused by mutations or disruptions in the DNA sequences and regulatory elements that guide the spliceosome, leading to incorrect removal of introns and joining of exons.Molecular MechanismsPre-mRNA splicing is a highly regulated process where introns are removed and exons joined to form mature mRNA. This process relies on cis-acting elements such as splice donor and acceptor sites, branch points, polypyrimidine tracts, and exonic or intronic splicing enhancers and silencers, as well as trans-acting factors like spliceosomal proteins and small nuclear RNAs (snRNAs) that recognize these sequences . Abnormal splicing occurs when these elements are altered or misrecognized.Genetic CausesPoint Mutations at Consensus Sequences: Mutations at the canonical splice donor or acceptor sites can prevent the spliceosome from correctly identifying exon-intron boundaries, resulting in exon skipping, intron retention, or activation of cryptic splice sites .Mutations in Splicing Regulatory Elements: Changes in exonic or intronic splicing enhancers or silencers can disrupt normal splicing regulation, leading to aberrant inclusion or exclusion of exons .Deep Intronic Mutations: Mutations far from the canonical splice sites can create new cryptic splice sites or interfere with branch point recognition, causing abnormal splicing patterns .Synonymous and Nonsynonymous Variants: Even mutations that do not change the amino acid sequence can affect splicing by altering regulatory motifs, leading to defective mRNA .Functional ConsequencesAbnormal splicing can produce mRNA with frameshifts, premature stop codons, or missing exons, resulting in truncated or nonfunctional proteins. This mechanism underlies many genetic disorders, including Spinal Muscular Atrophy, Cystic Fibrosis, Duchenne Muscular Dystrophy, and certain cancers .Additional FactorsDisruption of Spliceosome Components: Mutations in proteins or RNAs that form the spliceosome can globally affect splicing fidelity.Epigenetic and Environmental Influences: DNA methylation, histone modifications, or cellular stress can indirectly affect splicing efficiency and accuracy. Understanding these causes is critical for diagnosis and therapeutic intervention, such as the use of antisense oligonucleotides to correct aberrant splicing .