Skin is the largest organ in the body that protects the organism from environmental, chemical and physical traumas of each passing day. The protective skin epidermal permeability barrier (EPB) is formed within the exterior layers of the epidermis, which are regularly sloughed off and repopulated by movement of inner cells. The epidermal permeability barrier is established during in utero development and maintained through lifetime. Impaired epidermal barrier formation is one of the major features of several dermatoses such as psoriasis and atopic dermatitis. Chicken ovalbumin upstream promoter transcription factor (COUP-TF)-interacting protein 2 (Ctip2), also known as Bcl11b, is a C���H��� zinc finger protein expressed in many organs and tissues. It has been shown to regulate the development of thymocyte, tooth and corticospinal motor neurons. Ctip2 is highly expressed in mouse epidermis during skin organogenesis and in adulthood. It is crucial for epidermal homeostasis and protective barrier formation in developing mouse embryos. Germline (Ctip2- null mice) and selective ablation of Ctip2 in mouse epidermis (Ctip2[superscript ep-/-] mice) leads to increased transepidermal water loss (TEWL), impaired epidermal proliferation and terminal differentiation as well as altered lipid distribution during embryogenesis. Sphingolipids account for ~50% of total skin lipids by weight and are crucial components of epidermal barrier. We have recently identified Ctip2 as a key regulator of skin lipid metabolism. Germline deletion of Ctip2 in mouse embryos leads to altered lipid composition in the developing mouse epidermis by modulating the expression levels of key enzymes involved in lipid metabolism (bio-synthesis and catabolism). We also demonstrated that Ctip2 is recruited to the promoter regions of several genes involved in the ceramide and sphingomyelin biosynthesis pathways and could directly regulate their expression. Thus, we have identified Ctip2 as a key regulator of several lipid metabolizing genes and hence epidermal sphingolipid biosynthesis during skin development. To study the role of Ctip2 in adult skin homeostasis, we have utilized Ctip2[superscript ep-/-] mouse model in which Ctip2 is selectively deleted in epidermal keratinocytes. We showed that keratinocytic ablation of Ctip2 leads to atopic dermatitis (AD)-like skin inflammation, characterized by alopecia, pruritus and scaling, as well as high infiltration of T lymphocytes and immune cells. We have also observed increased expression of Th2-type cytokines and chemokines in the mutant skin, as well as systemic immune responses that share similarity with human AD patients. Furthermore, we discovered that thymic stromal lymphopoietin (TSLP) expression is significantly upregulated in the mutant epidermis as early as postnatal day 1 and Ctip2 was recruited to the promoter region of the TSLP gene in mouse epidermal keratinocytes. The results suggest that upregulation of TSLP expression in the Ctip2[superscript ep-/-] epidermis could be due to a derepression of gene transcription in absence of Ctip2. Thus, our data demonstrated a cell-autonomous role of Ctip2 in barrier maintenance and epidermal homeostasis in adult skin, as well as a non-cell autonomous role of keratinocytic Ctip2 in suppressing skin inflammatory responses by regulating the expression of Th2-type cytokines in adult mouse skin. Present results establish an initiating role of epidermal TSLP in AD pathogenesis via a novel repressive regulatory mechanism mediated by Ctip2 in mouse epidermal keratinocytes. Altogether, our study indicates that Ctip2 could be involved in a diverse range of biological events in skin including barrier formation, maintenance and epidermal homeostasis. Ctip2 appears to be a master regulator in skin barrier functions by directly regulating the transcription of a subset of genes involved in lipid metabolism and inflammatory responses. / Graduation date: 2013