Skin epithelial development and regeneration involve multi-tiered regulatory mechanisms integrating multiple signaling and transcriptional activities to precisely control lineage choices as well as proliferation and differentiation within lineage. The epidermis forms during late embryogenesis from a single-layered surface ectoderm, and regenerates itself throughout postnatal life due to the presence of stem cells that are capable of recapitulating what happens during morphogenesis, namely self-renewal and producing transiently amplifying (TA) progenitor cells that subsequently exit cell cycle and terminally differentiate as they migrate toward the skin surface. The parent R01 of this revision application uses traditional experimental approaches to study the role of Ovol transcription factors, Ovol1 and Ovol2, in embryonic and postnatal epidermis. In this revision application, we propose a systems biology approach to improve the understanding of how Ovol and their upstream (e.g., TGF-2 signaling) and downstream factors work in an integrated fashion to control epidermal development. Specifically, we propose that the inclusion of Ovol proteins in the system is essential for the formation of an epidermis with a correct size and balanced lineage stages, 2) Ovol2 specifically regulates epidermal stem cell proliferation by repressing c-Myc. We will 1) develop mathematical models at both cellular (stem, TA, and differentiated cells) and molecular (TGF-2, c-Myc, Ovol) levels using constraints supplied by available data; 2) measure the actual number of stem, TA, and differentiated cells, proliferation index, and epidermal thickness under wild-type and Ovol-deficient conditions, and use both in vitro and in vivo data to validate and refine our models; 3) simulate and analyze the models to make predications on the roles of Ovol and its interactions with other components, such as c-Myc and TGF-2, and test the predications experimentally whenever possible; 4) if time permits, incorporate into modeling additional complexity of the system such as spatial heterogeneity, and additional molecular players such as Wnt/2-catenin and Notch signaling. Insights generated from these studies may well translate into testable hypotheses and long-term projects to understand not only epidermal development but also regeneration. ? ? ?
The proliferation and differentiation of a stem/progenitor cell is important for building a tissue with the correct final size and cell compositions - too much proliferation may cause cancer, whereas too little proliferation will not generate the desired tissue. The proposed systems biology studies will help us better understand how proliferation/differentiation of stem/progenitor cells of the epidermis is regulated. They have the potential to identify critical targets for psoriasis and cancer treatment and provide fundamental knowledge necessary to design successful stem cell therapy.
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