Gene Regulatory Mechanisms in Epithelial Specification and Function

As epithelial tissues, the cornea epithelium and epidermis share many functional, morphological and regulatory similarities. They both serve important barrier functions, protecting the organism and underlying tissues from the external environment, and undergo constant cell turnover, requiring a precise balance of proliferation and differentiation to maintain tissue integrity. To accomplish this balancing act, they make use of similar mechanisms, and integrate information from pre-existing regulatory domains with the expression and actions of lineage-specific transcriptional regulators. The importance of transcription factor binding to distal regulatory regions is demonstrated by our finding that SNPs linked to disease in cornea or epidermis cause alterations in enhancing ability, and disrupt transcription factor motifs, a potential mechanism underlying the observed increased risk for disease. GRHL3 is an important regulator of both epidermal keratinocyte differentiation and migration; we have identified unique mechanisms of action for this single factor under the two different physiological conditions: GRHL3 associates with enhancers and super enhancers to activate structural and barrier genes in differentiating keratinocytes, and with promoters to repress genes involved in inhibition of migration. Selectivity may come about through differential association with co-factors during migration and differentiation. Based on opposing expression patterns for KLF4 and KLF7 in cornea epithelium, we characterize and define a role for KLF7 in maintaining corneal epithelial progenitor cells in an undifferentiated state, acting antagonistically to KLF4, a pro-differentiation factor. Our work with CLIMs points to the importance of these factors in corneal epithelium development and maintenance, in part through regulation of noncoding RNA H19