Mutations in the non-coding RNU4ATAC gene affect the homeostasis and function of the Integrator complex

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Pathogenic variants in U4atac small nuclear RNA (snRNA) are linked to microcephaly and developmental disorders.
• The minor spliceosome, including U4atac snRNA, is crucial for processing specific introns in mRNA.
• The molecular basis for most U4atac mutations remains poorly understood.

Purpose of the Study:

• To investigate the molecular consequences of compound heterozygous U4atac mutations (g.108_126del;g.111G>A) in patients with MOPD1.
• To analyze the impact of these mutations on small nuclear ribonucleoprotein (snRNP) formation and splicing efficiency.
• To explore the effects on the Integrator complex and its associated proteins.

Main Methods:

• Analysis of lymphoblastoid cells from compound heterozygous twin patients.
• Assessment of snRNP formation and stability.
• Splicing assays for minor introns.
• Protein level analysis of Integrator subunits.

Main Results:

• The U4atac108_126del mutant snRNA is unstable; U4atac111G>A mutant and minor snRNPs are reduced.
• Patients' cells exhibit 3'-extended snRNA transcripts.
• Mutant cells show altered splicing of INTS7 and INTS10 minor introns, reduced INTS7/INTS10 protein levels, and disrupted Integrator complex assembly.

Conclusions:

• Compound heterozygous g.108_126del;g.111G>A mutations in U4atac snRNA lead to splicing defects.
• These mutations impair the homeostasis and function of the Integrator complex.
• This provides molecular insight into U4atac-related microcephaly and developmental disorders.