Impact of histone H2A and H2B variants on human intestinal stem cells identity

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Chromatin organization plays a key role in cell fate, self-renewal, and maintenance of multi- or pluripotency state in human stem cells. Modulation of nucleosome configuration, through the incorporation of different histone variants, represents an important aspect of epigenetic transcriptional regulation. Thus, enrichment of specific genomic regions with specialized nucleosomes is critical to establishing cellular identity. Human intestinal crypt is an ideal model to study the fundamental balance between cell proliferation and differentiation, which maintains a constant renewal of the intestinal luminal surface. Thus, applying cutting-edge concepts in epigenetics, to the tightly regulated cell functions in the human intestinal crypt represents a unique opportunity to increase our basic knowledge in cell biology.******The intestinal crypt contains two distinct stem cell populations, respectively known to be actively cycling (LGR5HI) and quiescent (LGR5LO). The interplay between these two intestinal stem cell (ISC) populations is essential to maintain long-term tissue homeostasis. Although, the developmental origin of ISCs is well characterized, little is known about the mechanisms responsible for preservation of distinct functional identity between LGR5HI and LGR5LO ISCs.***Based on preliminary results and current literature, we hypothesize that defined H2A and H2B histone variants play a key role in maintaining LGR5HI and LGR5LO ISC populations. Thus, mutually exclusive shifts occurring in the incorporation of H2A and H2B variants within nucleosomes of distinct loci would impact the expression of key genes involved in ISC identity. The histone variants identified from preliminary experiments possess key structural features, conferring them specific DNA and internucleosomal interaction properties and consequently, distinct transcriptional regulation potentials.******Using a robust cellular model of human ISC interconversion, we aim at defining the contribution of histone H2A and H2B variants on human intestine tissue architecture and homeostasis. First, we will characterize the distribution pattern of each histone variant in LGR5HI vs. LGR5LO ISCs. Using established genetic tools, we will manipulate the expression levels of each studied histone variants in cultured human ISCs and determine their role on ISC-specific gene signature and how it reflects on cell-cycle regulation, as well as differentiation potential. Finally, using a unique system of extracellular matrix screening arrays, we will identify the contribution of microenvironment cues from the extracellular matrix in the establishment of ISC epigenetic landscape. ******Our work will advance basic knowledge to provide novel insights into epigenetic regulation of cellular identity, and a better understanding of the equilibrium between somatic stem cell populations maintaining tissular integrity.