Poster Sessions

Mol-21

Reini Luco

R. Luco, T. Misteli

Crosstalk between epigenetic histone marks and alternative splicing

Alternative splicing is a general mechanism important for generating protein diversity. Increasing evidence indicates that alternative splicing occurs co-transcriptionally and that splicing outcome is influenced by transcription. We now demonstrate that epigenetic chromatin modifications contribute to regulation of alternative splicing. We use exons IIIb and IIIc of the membrane receptor gene FGFR2 which are mutually exclusively spliced in a tissue-specific fashion. Comparison of the relative enrichment of several major histone modifications along the alternatively spliced region of FGFR2 in human epithelial PNT2 cells, where IIIb is included, and in mesenchymal stem cells, where IIIc is included, revealed distinct sets of histone modifications over the alternatively spliced regions. In PNT2 cells, the alternatively spliced region is enriched in histone marks usually found in promoter regions, including H3-K4me3, H3-K27me3 and K9me1. In contrast, in hMSC the region is rich in H3-K36me3. Consistent with these differential enrichments, the H3-K4 demethylase complex MRG15 was also enriched along the alternative spliced region in hMSC. Moreover modulation of H3-K4me3 and H3-K36me3 by overexpression of MRG15 and Set2, respectively increased IIIb exclusion in PNT2 cells. We propose that H3-K36me3 acts as a mark on chromatin for exon inclusion and that binding of MRG15 to an H3-K36me3-rich chromatin domain promotes exon usage. We are currently delineating the molecular basis of the crosstalk between histone modifications and the splicing machinery. The uncovered relationship between chromatin and RNA biogenesis represents a novel aspect of gene regulation. Its elucidation will provide conceptually and mechanistically novel insights into regulation of gene expression and has implications for the development of new therapeutic strategies for human splicing diseases and cancer.