Project Summary/Abstract Background: Transcriptional mechanisms that regulate epidermal homeostasis have been well established but recently we have discovered that mRNA export mechanisms play prominent roles in maintaining epidermal self-renewal. We have shown that RBM15 associates with the NXF1 exporter only in stem and progenitor cells while ZC3H18 associates with NXF1 in differentiated cells. This association allows RBM15 or ZC3H18 to control the mRNA export of key transcripts involved in epidermal growth and differentiation. Objective/hypothesis: This proposal seeks to understand the regulation of epidermal stem and progenitor cell self-renewal and differentiation through post-transcriptional mechanisms. We have identified RNA binding proteins that are necessary for the export of self-renewal mRNAs to promote epidermal self-renewal. Similarly we have identified RNA binding proteins that are necessary to export differentiation inducing mRNAs to promote epidermal differentiation. Furthermore mutations in these proteins can lead to clonal expansion of the skin due to altered regulation of epidermal growth and differentiation. Specific Aims: (1) To determine the role of RBM15 and ZC3H18 on epidermal growth and differentiation. (2) To determine the molecular mechanisms of RBM15 and ZC3H18 wildtype and mutant proteins impact on epidermal homeostasis. Study Design: To study epidermal homeostasis in a more clinically relevant setting, we generate 3-dimensionally intact human skin, containing human epidermal cells (that have been permanently knocked down for RBM15 or ZC3H18) in the context of human dermal stroma and basement membrane, regenerated on immune compromised mice. By using this model, we can perform loss of function experiments on RBM15 or ZC3H18 in regenerated human skin to characterize their role in epidermal growth and differentiation. We will also use RNA immunoprecipitations followed by next generation sequencing to determine the RNAs associated with these proteins.