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Compound heterozygous mutations in the noncoding RNU4ATAC gene affect the homeostasis and function of the Integrator complex

ABSTRACT: Various genetic diseases associated with microcephaly and developmental defects are due to pathogenic variants in the U4atac snRNA, a component of the minor spliceosome essential for the removal of U12-type introns from eukaryotic messenger RNAs. While it has been shown that a few RNU4ATAC mutations result in impaired binding of essential protein components, the molecular defects of the vast majority are still unknown. Here, we used cells derived from two RNU4ATAC compound heterozygous (g.108_126del;g.111G>A) twin patients with MOPD1 phenotypes to analyze the molecular consequences of the mutations on snRNPs formation and splicing. We show that the U4atac108_126del mutant is unstable and that the 111G>A mutation located in the apical 3’ stem-loop of U4atac induces defects in 3’-end maturation giving rise to decreased levels of mature U4atacG111A snRNA as well as of minor di- and tri-snRNPs. We also found that the mutant cells have alterations in splicing of minor introns and contain lower levels of INTS7 and INTS10 proteins. Altogether, our results demonstrate that the compound heterozygous g.108_126del;g.111G>A U4atac mutations lead to defects in 3’-end processing of U4atac transcripts and affect the homeostasis and function of the Integrator complex.

ORGANISM(S): Homo sapiens

PROVIDER: GSE197344 | GEO | 2022/12/01

REPOSITORIES: GEO

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Project description:U12-type introns were originally recognized based on their highly conserved non-consensus AT-AC termini1,2, which are spliced by a separate minor spliceosome3,4. Padgett and Krainer groups later showed that terminal dinucleotides do not differentiate U12-type from U2-type introns, as there are U12-type introns with GT-AG termini and U2-type introns with AT-AC termini5,6. Rather, U12-type introns are recognized by their divergent and highly conserved 5’ splice site (5’ss) and branch point sequences, which both differ from the consensus sequences found in U2-type introns. To date, no functional differences have been ascribed to AT-AC or GT-AG subtypes of U12-type introns, nor have RNAseq analyses of minor spliceosome diseases reported any subtype specificity. Here, we describe a novel protein component of the minor spliceosome, encoded by the CENATAC locus, that is required for accurate splicing of AT-AC but not GT-AG type minor introns. CENATAC was initially identified in a subset of Mosaic Variegated Aneuploidy (MVA) patients with mutations in CENATAC, which lead to chromosome congression defects during mitosis. Earlier large-scale proteomic analyses tentatively classified CENATAC as a spliceosome component and phylogenetic analyses showed co-segregation of CENATAC with minor spliceosome components. Targeted depletion of CENATAC in HeLa cells, followed by RNAseq revealed global retention of AT-AC minor subtype introns with more than 60% showing statistically significant (up to 90%) intron retention (IR). Additionally, U12-type introns with 5’-AT, but divergent 3’-terminal dinucleotides also showed significant IR. We also detected cryptic U2-type splice site activation near affected AT-AC introns. In contrast, about 10% of GT-AG subtype introns responded to CENATAC depletion. Co-IP experiments revealed that CENATAC is not a U11/U12 di-snRNP component as expected for a specificity factor, but rather associates with the U4atac/U6atac.U5 tri-snRNP via interaction with PRPF3/4, suggesting a role for minor tri-snRNP in initial 5’ss recognition. CENATAC also interacts with TXNL4B, a paralog of TXNL4A in the major tri-snRNP. Finally, several genes encoding chromosome congression factors harbor U12 AT-AC-type introns that were highly retained in CENATAC depleted cells, potentially explaining the aneuploidy phenotype observed in MVA patients.

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Compound heterozygous mutations in the noncoding RNU4ATAC gene affect the homeostasis and function of the Integrator complex

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