The epidermis and skin appendages perform essential barrier functions that protect the body from environmental insults and maintain fluid-electrolyte balance. Defects in the development, differentiation, and proliferation of the cells tht comprise the skin and hair follicles lead to numerous diseases such as skin cancer, psoriasis, bullous skin disease, and alopecia. Transcriptional programs that control skin and hair follicle development have defined processes important for epidermal integrity and hair regeneration. More recently microRNAs have also emerged as important regulators of gene expression in the skin. In contrast, the role of alternative splicing (AS) in skin development and function is essentially unstudied~ there have been no publications focused on alternative splicing factors in the skin or its appendages. Reciprocal epithelial- mesenchymal interactions (EMIs) underlie formation of the epidermis and hair follicles. One important arm involves the interaction of mesenchymal derived Fgf7 and/or Fgf10 with an epithelial-specific splice isoform of fibroblast growth factor receptor 2, Fgfr2-IIIb. Fgf7 and Fgf10 specifically interact with Fgfr2-IIIb, but not mesenchymal Fgfr2-IIIc. Abrogation of this directional signaling pathway results in defects in the epidermis and hair follicles. My lab identified the epithelial-specific splicing factors Esrp1 and Esrp2 that are both necessary and sufficient for the expression of the Fgfr2-IIIb splice variant in epithelial cells. We generated Esrp1 and Esrp2 knockout mice and demonstrate that combined Esrp1/Esrp2 KO is lethal and results in epidermal hypoplasia, reduced follicle numbers, and sparse hair. We hypothesize that the Esrps are required for normal epidermal and follicular development and function by enforcing the expression of epithelial-specific splice isoforms. We will determine the phenotypes of Esrp deletion in specific epithelial cell populations in skin and appendages and identify a comprehensive set of Esrp target transcripts through the following Aims: 1) Determine the phenotypes associated with Esrp ablation in the interfollicular epidermis and in hair follicles. We will define phenotypes associated with conditionally ablation of the Esrps in developing and adult epidermis and hair follicles. 2) Define comprehensive programs of Esrp regulated alternative splicing in the epidermis and hair follicle. We will use high throughput sequencing (RNA-Seq) and splicing sensitive microarrays to define genome-wide programs of alternative splicing in the different cell populations that populate the skin. These technologies will be used in conjunction with conditional deletion strategies to define Esrp regulated targets i the epidermis and hair follicle stem cells. The proposed aims constitute the first comprehensive analysis of alternative splicing in skin development and function, thereby introducing a new paradigm to the field. These studies will reveal novel insights into the processes that impact skin development and function.