Epigenetic Regulation of Skin Development and Postnatal Homeostasis The role of chromatin architectural protein Ctcf in the control of Keratinocyte Differentiation and Epidermal Barrier Formation

Abstract

Epigenetic regulatory mechanisms play important roles in the control of lineage-specific differentiation during development. However, mechanisms that regulate higher-order chromatin remodelling and transcription of keratinocyte-specific genes that are clustered in the genome into three distinct loci (Keratin type I/II loci and Epidermal Differentiation Complex (EDC) during differentiation of the epidermis are poorly understood. By using 3D-Fluorescent In Situ Hybridization (FISH), we determined that in the epidermal keratinocytes, the KtyII and EDC loci are located closely to each other in the nuclear compartment enriched by the nuclear speckles. However, in KtyII locus knockout mice, EDC locus moved away from the KtyII locus flanking regions and nuclear speckles towards the nuclear periphery, which is associated with marked changes in gene expression described previously. Chromatin architectural protein Ctcf has previously been implicated in the control of long-range enhancer-promoter contacts and inter-chromosomal interactions. Ctcf is broadly expressed in the skin including epidermal keratinocytes and hair follicles. Conditional Keratin 14-driven Ctcf ablation in mice results in the increase of the epidermal thickness, proliferation, alterations of the epidermal barrier and the development of epidermal pro-inflammatory response. Epidermal barrier defects in Krt14CreER/Ctcf fl/fl mice are associated with marked changes in gene expression in the EDC and KtyII loci, which become topologically segregated in the nucleus upon Ctcf ablation. Therefore, these data suggest that Ctcf serves as critical determinant regulating higher-order chromatin organization in lineage-specific gene loci in epidermal keratinocytes, which is required for the proper control of gene expression, maintenance of the epidermal barrier and its function.