CRISPR Disruption of scaRNA1 Reduces Pseudouridylation in Spliceosomal RNA U2 at U89 and Perturbs the Transcriptome in HEK293T Cells

Small Cajal body-associated RNAs (scaRNAs) are essential for biochemical modification of spliceosomal RNAs and spliceosome function. Changes in scaRNA expression level have been associated with developmental issues, including cancer and congenital heart defects (CHDs), although the mechanism remains unclear. Small Cajal body-associated RNA 1 (scaRNA1) guides pseudouridylation at uridine 89 (Ψ89) of the spliceosomal RNA U2, a highly conserved modification that may be critical for spliceosome function. To investigate the role of scaRNA1 in splicing regulation, CRISPR-Cas9 genome editing was used to introduce targeted deletions in the scaRNA1 locus in HEK293T cells. Edited clones were identified by T7 endonuclease I assay and confirmed by Sanger sequencing. Pseudouridylation at Ψ89 was quantified using CMC-based reverse transcription followed by quantitative PCR, and global mRNA splicing alterations were assessed by RNA sequencing. Clones harboring scaRNA1 disruptions exhibited a significant reduction in Ψ89 pseudouridylation, consistent with impaired scaRNA1 function. Transcriptome analysis (of mRNA from two clones) revealed >300 protein coding genes with significant changes in transcript isoform level, including >100 genes related to RNA-binding activity. These results indicate that scaRNA1 disruption alters spliceosomal function and leads to substantial changes in mRNA splicing. The dysregulated splicing of RNA-binding proteins may impair RNA processing and gene expression programs required for normal development, providing new insight into how noncoding RNA dysfunction may contribute to developmental pathogenesis.