A novel intra-U1 snRNP cross-regulation mechanism: alternative splicing switch links U1C and U1-70K expression.

Tanja Dorothe Rösel-Hillgärtner, Lee-Hsueh Hung, Ekaterina Khrameeva, Patrick Le Querrec, Mikhail S Gelfand, Albrecht Bindereif

PLoS genetics 2013

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The U1 small nuclear ribonucleoprotein (snRNP)-specific U1C protein participates in 5' splice site recognition and regulation of pre-mRNA splicing. Based on an RNA-Seq analysis in HeLa cells after U1C knockdown, we found a conserved, intra-U1 snRNP cross-regulation that links U1C and U1-70K expression through alternative splicing and U1 snRNP assembly. To investigate the underlying regulatory mechanism, we combined mutational minigene analysis, in vivo splice-site blocking by antisense morpholinos, and in vitro binding experiments. Alternative splicing of U1-70K pre-mRNA creates the normal (exons 7-8) and a non-productive mRNA isoform, whose balance is determined by U1C protein levels. The non-productive isoform is generated through a U1C-dependent alternative 3' splice site, which requires an adjacent cluster of regulatory 5' splice sites and binding of intact U1 snRNPs. As a result of nonsense-mediated decay (NMD) of the non-productive isoform, U1-70K mRNA and protein levels are down-regulated, and U1C incorporation into the U1 snRNP is impaired. U1-70K/U1C-deficient particles are assembled, shifting the alternative splicing balance back towards productive U1-70K splicing, and restoring assembly of intact U1 snRNPs. Taken together, we established a novel feedback regulation that controls U1-70K/U1C homeostasis and ensures correct U1 snRNP assembly and function.

Citation

Tanja Dorothe Rösel-Hillgärtner, Lee-Hsueh Hung, Ekaterina Khrameeva, Patrick Le Querrec, Mikhail S Gelfand, Albrecht Bindereif. A novel intra-U1 snRNP cross-regulation mechanism: alternative splicing switch links U1C and U1-70K expression. PLoS genetics. 2013;9(10):e1003856