Biological Significance of the Histone Variant H3.3, 2015

In the eukaryotic cell nucleus, the genome is organized into chromatin domains with different physical, biochemical and functional properties influencing gene expression and developmental decisions. These domains can be distinguished by their enrichment in combinations of post translational modified histones and in variants of canonical histones. While the distribution and significance of epigenetic histone modifications have been extensively examined since the discovery of the histone code 10 years ago, little is known on the significance of histone variants. Nonetheless, a recent burst of publications reflects strong interest in elucidating the role of these variants. Among these, the H3 variant H3.3 incorporates into primarily (but not solely) transcriptionally active chromatin in a replication independent manner. The mode of insertion of H3.3 into chromatin, its positioning in the genome and its requirement for vertebrate development remain elusive. We have recently reported the epigenetic environment of H3.3 in human promoters and have gathered preliminary data on its deposition pathway. Here, we combine expertise in mesenchymal stem cell biology, imaging, epigenetics and cell differentiation together with state-of-the-art high-throughput sequencing and mass spectrometry technologies, to address the biological meaning of insertion of H3.3 in the genome in a cell differentiation context. Our goal is to characterize in detail the molecular mechanism of incorporation of H3.3 into chromatin and get a hint at its function in cellular differentiation. OBJECTIVE 1 aims to provide full genome coverage of H3.3 enrichment sites, in human primary progenitor cells and differentiated cells. OBJECTIVE 2 aims to elucidate the mechanistic details of H3.3 incorporation into chromatin, by characterizing H3.3 'transit sites' which we have recently evidenced. This project is a part of the FRIMEDBIO-program.