- A role of intragenic chromatin structure in co-transcriptional RNA processing

SCHOR IE; FISZBEIN A; LLÈRES D; LAMOND AI; KORNBLIHTT AR

Heidelberg

Conferencia; EMBO Conference “Chromatin and Epigenetics”; 2011

EMBO

Chromatin structure is connected to the exon-intron architecture of genes, including specific nucleosome positioning in exons as well as histone and DNA modifications. In addition, our previous work shows an example of how intragenic chromatin modulation can affect alternative splicing: depolarization of the membrane potential of neuronal cells triggers an increase in intragenic H3 acetylation along the NCAM gene, which results in skipping of the alternative exon 18 (E18) from the mature mRNA. We also detected an increase of total histone acetylation and of CBP acetyl-transferase expression after depolarization treatment, suggesting a more general role of histone acetylation. We observed a redistribution of SC35 and SF2/ASF splicing factors in response to both depolarization and the hyper-acetylating drug trichostatin A (TSA): a decrease in nucleoplasmic localization and enlargement of nuclear speckles. The same is seen in HeLa cells for several alternative and constitutive splicing factors. Since TSA also impairs inclusion of different exons, we interpret that disruption of normal chromatin structure causes a decrease in the co-transcriptional recognition of splice sites by splicing factors. Using the NCAM E18 exon as a model, we found evidence that neuronal differentiation of N2a cells causes, contrary to what is seen after depolarization, intragenic increase in transcription-repressive histone modifications (H3K9me2 and H3K27me3) which correlates with enhanced E18 inclusion. Also, differentiation-induced inclusion can be reversed by treatment with DNA and histone methyltransferases inhibitors. Using available ChIP-seq and splicing microarray data we were able to find other genes with apparent chromatin-dependent regulation of alternative splicing during neuronal differentiation. This leads to a model where intragenic chromatin can be physiologically modulated in both directions (repressive/permissive) with functional consequences to coupled alternative splicing.