Genome-wide analysis of histone modifications H3K27ac, H3K4me3, and H3K4me1 in migrating primary human epidermal keratinocytes (NHEK)

The epidermis is a stratified squamous epithelium that serves to protect the body from dehydration, absorption of chemicals, and invasion of pathogens. It derives from the surface ectoderm during the later stages of mammalian embryonic development. In a stratified squamous epithelium cells of the basal layer contain proliferative potential. As they divide and move upward in the tissue, they progressively differentiate, and activate the gene expression program required to create a barrier; eventually, cells in the uppermost layer are sloughed off from the surface of the epidermis. This system requires continual replacement of differentiating cells from the basal layer. Such a process requires very precise regulation of gene expression to balance proliferation and differentiation and maintain a functioning epithelium. A number of transcription factors are known to be crucial to maintaining this balance; among these are p63, Notch, c-myc, Klf4, and Grhl3. These factors interact in a complex epidermal differentiation network, where the contributions of each factor provide balance and precision to the process of differentiation. When the epidermal barrier is breached due to wounding, a cascade of cytokines and other signaling molecules activate a wound healing program of gene expression, inducing everything from blood clotting, immune cell infiltration of the skin, regrowth of blood and lymph vessels, and the coordinated keratinocyte migration into the center of the wound followed by stratification, all of which is required to regenerate the lost tissue. ChIP experiments for histone modifications H3K27ac, H3K4me1, and H3K4me3 were performed on primary human epidermal keratinocyte cells that had been grown to 95% confluency and scratched with a pipet tip to induce migration, cells were collected for ChIP after 12 hours.