Transcription-coupled RNA surveillance in human genetic diseases caused by splice site mutations

Area of Science:

• Molecular Biology
• Genetics
• RNA Biology

Background:

• Approximately one-third of disease-causing mutations disrupt RNA splicing.
• Abnormal splicing often leads to premature termination codons (PTCs) and mRNA degradation via nonsense-mediated decay (NMD) in the cytoplasm.
• The role of nuclear RNA quality control mechanisms in human genetic diseases remains largely unknown.

Purpose of the Study:

• To investigate how splice site mutations (SM) affect messenger RNA (mRNA) biogenesis.
• To determine the significance of nuclear RNA surveillance in the context of human genetic diseases caused by splicing defects.

Main Methods:

• Utilized patient-derived lymphoblastoid cell lines as disease models.
• Analyzed mRNA levels associated with chromatin and in the cytoplasm.
• Quantified nascent transcripts to assess transcriptional activity.
• Treated cells with cycloheximide, a translation inhibitor, to differentiate between NMD-dependent and independent mechanisms.

Main Results:

• Most splicing mutations introduced PTCs and triggered cytoplasmic mRNA degradation via NMD.
• A subset of mutant transcripts showed reduced RNA levels associated with chromatin.
• Genes with splicing mutations exhibited reduced transcriptional activity.
• Cycloheximide treatment increased cytoplasmic mutant RNA levels but did not affect chromatin-associated transcripts, suggesting a transcription-coupled surveillance mechanism.

Conclusions:

• Transcription-coupled RNA surveillance operates independently of NMD to mitigate cellular levels of abnormal RNAs resulting from splicing mutations.
• Nuclear RNA quality control mechanisms play a significant role in managing the cellular impact of splicing defects in human genetic diseases.