GSE39748
Argonaute proteins couple chromatin silencing to alternative splicing (RNA IP-Seq)
While Argonaute (AGO) proteins play a major role in transcriptional gene silencing (TGS) in many organisms, their role in the nucleus of somatic mammalian cells remains elusive. Here, we have purified AGO1 and AGO2 chromatin-embedded complexes, and found these proteins associated with previously described partners, but also with chromatin modifiers and, rather unexpectedly, with different splicing factors. Using the CD44 gene as a model for alternative splicing, we show that both AGO1 and AGO2 are required for Protein Kinase C (PKC)-dependent variant exon inclusion. AGO proteins facilitate the spliceosome recruitment and modulate the elongation rate of RNA polymerase II (RNAPII). The recruitment of AGO proteins to CD44 transcribed region is dependent on both the endonuclease Dicer and the chromodomain-containing protein HP1g, and results in locally increased levels of histone H3 lysine 9 (H3K9) methylation on variant exons. Genome wide analysis of splicing in either AGO2 or Dicer null cells showed that the two proteins have similar effects on many splicing events. Finally, sRNAs associated with nuclear AGO2 are mostly in sense orientation relative to protein-coding genes, supporting a role for intragenic antisense non-coding RNAs in the recruitment AGO and splicing factors. Together, our data demonstrate for the first time that the endogenous RNAi pathway is involved in alternative splicing decisions, unravelling a new model in which AGO proteins couple RNAPII elongation and chromatin modification. Overall design: Deep sequencing of small RNAs (approx. 15-80 nucleotides) bound to either cytoplasmic or chromatin-associated AGO2 complex.