Impact of LARP7 depletion on the transcriptome of HEK293 cells

The La-related protein LARP7 has been mainly described as a component of the 7SK small nuclear ribonucleoprotein (snRNP) complex, which negatively regulates RNA polymerase II by sequestering the positive transcription elongation factor b (P-TEFb). In our studies, we discovered a novel, 7SK snRNP-independent function of LARP7. We show that LARP7 interacts with the U6 spliceosomal RNA as well as with the small nucleolar RNAs (snoRNAs) directing the 2'-O-methylations of U6. Importantly, in the absence of LARP7, significantly less 2'-O-methylations are deposited on U6 affecting splicing fidelity. Mutations in the LARP7 gene have been associated with the Alazami syndrome, a form of primordial dwarfism characterized by intellectual disability. We describe a novel loss-of-function mutation of LARP7 occurring in Alazami patients and detect reduced 2'-O-methylations of U6 in patient-derived samples. Thus, aberrant posttranscriptional RNA modifications of the spliceosomal U6 snRNA may contribute to the development of this severe disease. Overall design: Analysis of the impact of LARP7 depletion on the expression and the alternative splicing of RNA transcripts. Two replicates each of parental HEK293 cells and HEK293 LARP7 knockout cells (clone 1-11) were used for total RNA sequencing.